fix(render): anchor video to clicked block's bottom-left, EAST/WEST flush

Three fixes for v0.4.1:

1. Video stick item rendered as missing-texture because 26.1.2 requires the
   new client_item descriptor at assets/<mod>/items/<name>.json. Add it; the
   existing models/item/video_stick.json is kept as the underlying model.

2. Quad placement now anchors the local (0,0) corner at the bottom-left of
   the wall face the player clicked, so the clicked block is the BL and the
   video grows up & right. Previously it was centered on the anchor.

3. EAST/WEST face rotations were swapped, which placed the quad on the far
   side of the air block (~1 block away from the wall) instead of flush.
   Derived the correct rotations from first principles:
     EAST = Axis.YP +90°  (local +Z → world +X, +X → -Z = north)
     WEST = Axis.YP -90°  (local +Z → world -X, +X → +Z = south)
   NORTH/SOUTH/UP/DOWN math re-verified — those were already correct.

.gitea/workflows/build.yml

@@ -0,0 +1,23 @@
+name: build
+
+on:
+  push:
+    branches: [main]
+    tags: ["v*"]
+  pull_request:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-java@v4
+        with:
+          distribution: temurin
+          java-version: 25
+      - name: Build (MC 26.1.2)
+        run: ./gradlew --no-daemon build
+      - uses: actions/upload-artifact@v4
+        with:
+          name: video_player-mc26.1.2
+          path: build/libs/*.jar

build.gradle

@@ -1,5 +1,5 @@
 plugins {
-    id 'fabric-loom' version '1.16.2'
+    id 'net.fabricmc.fabric-loom' version "${loom_version}"
     id 'maven-publish'
     id 'java'
 }
@@ -16,33 +16,41 @@ repositories {
     maven { url = 'https://maven.fabricmc.net/' }
 }
 
+loom {
+    // Intentionally empty — MC 26.1+ ships unobfuscated, so the new loom does not remap.
+}
+
 dependencies {
+    // No mappings dep — Mojang ships official names since 26.1, intermediary is gone.
     minecraft "com.mojang:minecraft:${project.minecraft_version}"
-    mappings "net.fabricmc:yarn:${project.yarn_mappings}:v2"
+
-    modImplementation "net.fabricmc:fabric-loader:${project.loader_version}"
+    implementation "net.fabricmc:fabric-loader:${project.loader_version}"
-    modImplementation "net.fabricmc.fabric-api:fabric-api:${project.fabric_version}"
+    implementation "net.fabricmc.fabric-api:fabric-api:${project.fabric_version}"
 }
 
 processResources {
     inputs.property "version", project.version
     inputs.property "mod_id", project.mod_id
+    inputs.property "minecraft_version", project.minecraft_version
 
     filesMatching("fabric.mod.json") {
-        expand "version": project.version, "mod_id": project.mod_id
+        expand "version": project.version,
+               "mod_id": project.mod_id,
+               "target_minecraft": "~${project.minecraft_version}"
     }
 }
 
 tasks.withType(JavaCompile).configureEach {
-    it.options.release = 21
+    it.options.release = 25
 }
 
 java {
     withSourcesJar()
-    sourceCompatibility = JavaVersion.VERSION_21
+    sourceCompatibility = JavaVersion.VERSION_25
-    targetCompatibility = JavaVersion.VERSION_21
+    targetCompatibility = JavaVersion.VERSION_25
 
     toolchain {
-        languageVersion = JavaLanguageVersion.of(21)
+        languageVersion = JavaLanguageVersion.of(25)
     }
 }
 

gradle.properties

@@ -1,14 +1,16 @@
 org.gradle.jvmargs=-Xmx2G
 org.gradle.parallel=true
+# Config cache disabled — new loom + IntelliJ aren't fully compatible yet
+org.gradle.configuration-cache=false
 
 # Mod
 mod_id=video_player
-mod_version=0.1.0
+mod_version=0.4.1
 maven_group=com.ejclaw.videoplayer
 archives_base_name=video_player
 
-# Minecraft / Fabric (1.21.6)
+# Minecraft / Fabric (26.1.2 — single target, intermediary/Yarn retired)
-minecraft_version=1.21.6
+minecraft_version=26.1.2
-yarn_mappings=1.21.6+build.1
 loader_version=0.19.2
-fabric_version=0.120.1+1.21.6
+loom_version=1.16-SNAPSHOT
+fabric_version=0.149.0+26.1.2

src/main/java/com/ejclaw/videoplayer/VideoPlayerClient.java

@@ -1,15 +1,84 @@
 package com.ejclaw.videoplayer;
 
+import com.ejclaw.videoplayer.block.VideoAnchorBlockEntity;
+import com.ejclaw.videoplayer.client.net.ClientNetworking;
+import com.ejclaw.videoplayer.client.playback.VideoPlayback;
+import com.ejclaw.videoplayer.client.render.VideoAnchorRenderer;
+import com.ejclaw.videoplayer.item.VideoStickItem;
+import com.ejclaw.videoplayer.net.DeleteAnchorPayload;
+import com.ejclaw.videoplayer.registry.VideoPlayerBlockEntities;
 import net.fabricmc.api.ClientModInitializer;
 import net.fabricmc.api.EnvType;
 import net.fabricmc.api.Environment;
+import net.fabricmc.fabric.api.client.event.lifecycle.v1.ClientTickEvents;
+import net.fabricmc.fabric.api.client.networking.v1.ClientPlayNetworking;
+import net.fabricmc.fabric.api.client.rendering.v1.BlockEntityRendererRegistry;
+import net.fabricmc.fabric.api.event.player.AttackBlockCallback;
+import net.minecraft.client.Minecraft;
+import net.minecraft.client.player.LocalPlayer;
+import net.minecraft.core.BlockPos;
+import net.minecraft.world.InteractionResult;
+import net.minecraft.world.phys.Vec3;
 
 @Environment(EnvType.CLIENT)
 public class VideoPlayerClient implements ClientModInitializer {
+
     @Override
     public void onInitializeClient() {
-        // M2+: BlockEntityRendererFactories.register(...)
+        ClientNetworking.register();
-        // M5+: AttackBlockCallback for left-click delete
+
-        VideoPlayerMod.LOG.info("[{}] client initialized (M1 scaffold)", VideoPlayerMod.MOD_ID);
+        BlockEntityRendererRegistry.register(
+            VideoPlayerBlockEntities.VIDEO_ANCHOR,
+            VideoAnchorRenderer::new
+        );
+
+        AttackBlockCallback.EVENT.register((player, level, hand, pos, direction) -> {
+            if (!level.isClientSide()) return InteractionResult.PASS;
+            if (!(player.getMainHandItem().getItem() instanceof VideoStickItem)) return InteractionResult.PASS;
+            // The anchor itself is invisible / non-collidable so the player cannot left-click it
+            // directly. Sneak + left-click on the wall the video sits on → delete the anchor in
+            // the adjacent air block.
+            if (player.isShiftKeyDown()) {
+                BlockPos anchorPos = pos.relative(direction);
+                if (level.getBlockEntity(anchorPos) instanceof VideoAnchorBlockEntity) {
+                    ClientPlayNetworking.send(new DeleteAnchorPayload(anchorPos));
+                    return InteractionResult.SUCCESS;
+                }
+            }
+            // Legacy / safety: if the player somehow targets the anchor block directly.
+            if (level.getBlockEntity(pos) instanceof VideoAnchorBlockEntity) {
+                ClientPlayNetworking.send(new DeleteAnchorPayload(pos));
+                return InteractionResult.SUCCESS;
+            }
+            return InteractionResult.PASS;
+        });
+
+        ClientTickEvents.END_CLIENT_TICK.register(client -> {
+            VideoPlayback.tick();
+            updateDistanceGains(client);
+        });
+
+        ClientTickEvents.END_LEVEL_TICK.register(world -> {
+            // no-op for now
+        });
+
+        VideoPlayerMod.LOG.info("[{}] client initialized", VideoPlayerMod.MOD_ID);
+    }
+
+    /** SPEC §6 — recompute per-anchor audio gain from player distance every tick. */
+    private static void updateDistanceGains(Minecraft client) {
+        LocalPlayer p = client.player;
+        if (p == null || client.level == null) return;
+        Vec3 eye = p.getEyePosition();
+        for (BlockPos pos : VideoPlayback.activePositions()) {
+            if (!(client.level.getBlockEntity(pos) instanceof VideoAnchorBlockEntity be)) continue;
+            double dx = (pos.getX() + 0.5) - eye.x;
+            double dy = (pos.getY() + 0.5) - eye.y;
+            double dz = (pos.getZ() + 0.5) - eye.z;
+            double d  = Math.sqrt(dx * dx + dy * dy + dz * dz);
+            float attenuation = (float) Math.max(0.0, Math.min(1.0, 1.0 - d / 16.0));
+            float gain = be.isMuted() ? 0F : be.getVolume() * attenuation;
+            VideoPlayback.setGain(pos, gain);
+        }
     }
 }

src/main/java/com/ejclaw/videoplayer/VideoPlayerMod.java

@@ -1,6 +1,10 @@
 package com.ejclaw.videoplayer;
 
+import com.ejclaw.videoplayer.command.VideoDeleteCommand;
+import com.ejclaw.videoplayer.command.VideoMuteCommand;
+import com.ejclaw.videoplayer.command.VideoPlaceCommand;
 import com.ejclaw.videoplayer.command.VideoStickCommand;
+import com.ejclaw.videoplayer.net.VideoPlayerNetwork;
 import com.ejclaw.videoplayer.registry.VideoPlayerBlockEntities;
 import com.ejclaw.videoplayer.registry.VideoPlayerBlocks;
 import com.ejclaw.videoplayer.registry.VideoPlayerItems;
@@ -19,10 +23,16 @@ public class VideoPlayerMod implements ModInitializer {
         VideoPlayerBlockEntities.register();
         VideoPlayerItems.register();
 
+        VideoPlayerNetwork.registerPayloadTypes();
+        VideoPlayerNetwork.registerServerReceivers();
+
         CommandRegistrationCallback.EVENT.register((dispatcher, registryAccess, env) -> {
             VideoStickCommand.register(dispatcher);
+            VideoPlaceCommand.register(dispatcher);
+            VideoDeleteCommand.register(dispatcher);
+            VideoMuteCommand.register(dispatcher);
         });
 
-        LOG.info("[{}] initialized (M1 scaffold)", MOD_ID);
+        LOG.info("[{}] initialized", MOD_ID);
     }
 }

src/main/java/com/ejclaw/videoplayer/block/VideoAnchorBlock.java

@@ -1,28 +1,90 @@
 package com.ejclaw.videoplayer.block;
 
+import com.ejclaw.videoplayer.item.VideoStickItem;
+import com.ejclaw.videoplayer.net.OpenScreenPayload;
 import com.mojang.serialization.MapCodec;
-import net.minecraft.block.AbstractBlock;
+import net.fabricmc.fabric.api.networking.v1.ServerPlayNetworking;
-import net.minecraft.block.Block;
+import net.minecraft.core.BlockPos;
-import net.minecraft.block.BlockEntityProvider;
+import net.minecraft.server.level.ServerPlayer;
-import net.minecraft.block.BlockState;
+import net.minecraft.world.InteractionHand;
-import net.minecraft.block.BlockWithEntity;
+import net.minecraft.world.InteractionResult;
-import net.minecraft.block.entity.BlockEntity;
+import net.minecraft.world.entity.player.Player;
-import net.minecraft.util.math.BlockPos;
+import net.minecraft.world.item.ItemStack;
+import net.minecraft.world.level.BlockGetter;
+import net.minecraft.world.level.Level;
+import net.minecraft.world.level.block.BaseEntityBlock;
+import net.minecraft.world.level.block.RenderShape;
+import net.minecraft.world.level.block.entity.BlockEntity;
+import net.minecraft.world.level.block.state.BlockBehaviour;
+import net.minecraft.world.level.block.state.BlockState;
+import net.minecraft.world.phys.BlockHitResult;
+import net.minecraft.world.phys.shapes.CollisionContext;
+import net.minecraft.world.phys.shapes.Shapes;
+import net.minecraft.world.phys.shapes.VoxelShape;
 
-public class VideoAnchorBlock extends BlockWithEntity implements BlockEntityProvider {
+/**
-    public static final MapCodec<VideoAnchorBlock> CODEC = createCodec(VideoAnchorBlock::new);
+ * Anchor block — invisible, non-collidable host for {@link VideoAnchorBlockEntity}.
+ *
+ * <p>The block exists only so a {@link BlockEntity} can be attached to a position; visually it is
+ * completely empty (no model, no selection outline, no collision). The video itself is drawn by
+ * {@link com.ejclaw.videoplayer.client.render.VideoAnchorRenderer} flush against the wall the
+ * player clicked, not as a textured surface on this block.
+ */
+public class VideoAnchorBlock extends BaseEntityBlock {
+    public static final MapCodec<VideoAnchorBlock> CODEC = simpleCodec(VideoAnchorBlock::new);
 
-    public VideoAnchorBlock(AbstractBlock.Settings settings) {
+    public VideoAnchorBlock(BlockBehaviour.Properties properties) {
-        super(settings);
+        super(properties);
     }
 
     @Override
-    protected MapCodec<? extends BlockWithEntity> getCodec() {
+    protected MapCodec<? extends BaseEntityBlock> codec() {
         return CODEC;
     }
 
     @Override
-    public BlockEntity createBlockEntity(BlockPos pos, BlockState state) {
+    public BlockEntity newBlockEntity(BlockPos pos, BlockState state) {
         return new VideoAnchorBlockEntity(pos, state);
     }
+
+    @Override
+    protected RenderShape getRenderShape(BlockState state) {
+        return RenderShape.INVISIBLE;
+    }
+
+    @Override
+    protected VoxelShape getShape(BlockState state, BlockGetter level, BlockPos pos, CollisionContext ctx) {
+        return Shapes.empty();
+    }
+
+    @Override
+    protected VoxelShape getCollisionShape(BlockState state, BlockGetter level, BlockPos pos, CollisionContext ctx) {
+        return Shapes.empty();
+    }
+
+    @Override
+    protected VoxelShape getOcclusionShape(BlockState state) {
+        return Shapes.empty();
+    }
+
+    @Override
+    protected boolean propagatesSkylightDown(BlockState state) {
+        return true;
+    }
+
+    @Override
+    protected InteractionResult useItemOn(ItemStack stack, BlockState state, Level level,
+                                          BlockPos pos, Player player, InteractionHand hand,
+                                          BlockHitResult hit) {
+        if (!(stack.getItem() instanceof VideoStickItem)) {
+            return InteractionResult.PASS;
+        }
+        if (level.isClientSide()) return InteractionResult.SUCCESS;
+        if (!(player instanceof ServerPlayer sp)) return InteractionResult.PASS;
+        if (level.getBlockEntity(pos) instanceof VideoAnchorBlockEntity be) {
+            ServerPlayNetworking.send(sp, new OpenScreenPayload(pos, be.toNbt()));
+            return InteractionResult.SUCCESS;
+        }
+        return InteractionResult.PASS;
+    }
 }

src/main/java/com/ejclaw/videoplayer/block/VideoAnchorBlockEntity.java

@@ -1,14 +1,18 @@
 package com.ejclaw.videoplayer.block;
 
 import com.ejclaw.videoplayer.registry.VideoPlayerBlockEntities;
-import net.minecraft.block.BlockState;
+import net.minecraft.core.BlockPos;
-import net.minecraft.block.entity.BlockEntity;
+import net.minecraft.core.Direction;
-import net.minecraft.util.math.BlockPos;
+import net.minecraft.nbt.CompoundTag;
-import net.minecraft.util.math.Direction;
+import net.minecraft.world.level.block.entity.BlockEntity;
+import net.minecraft.world.level.block.state.BlockState;
+import net.minecraft.world.level.storage.ValueInput;
+import net.minecraft.world.level.storage.ValueOutput;
 
 /**
- * M1 placeholder. Holds the runtime fields described in SPEC §3.1; NBT persistence
+ * Anchor BE — holds per-block config that drives playback.
- * (ReadView/WriteView in 1.21.6) lands in M3/M4 alongside the playback and GUI work.
+ * NBT persistence uses 26.1's ValueInput/ValueOutput.
+ * Network sync uses {@link #toNbt()} / {@link #fromNbt(CompoundTag)}.
  */
 public class VideoAnchorBlockEntity extends BlockEntity {
     private String url = "";
@@ -33,8 +37,88 @@ public class VideoAnchorBlockEntity extends BlockEntity {
     public boolean isMuted() { return muted; }
     public boolean isAutoplay() { return autoplay; }
 
-    public void setMuted(boolean muted) {
+    public void setUrl(String url) { this.url = url == null ? "" : url; setChanged(); }
-        this.muted = muted;
+    public void setWidth(int width) { this.width = clamp(width, 1, 32); setChanged(); }
-        markDirty();
+    public void setHeight(int height) { this.height = clamp(height, 1, 32); setChanged(); }
+    public void setFacing(Direction facing) { this.facing = facing == null ? Direction.NORTH : facing; setChanged(); }
+    public void setLoop(boolean loop) { this.loop = loop; setChanged(); }
+    public void setVolume(float volume) { this.volume = Math.max(0F, Math.min(1F, volume)); setChanged(); }
+    public void setMuted(boolean muted) { this.muted = muted; setChanged(); }
+    public void setAutoplay(boolean autoplay) { this.autoplay = autoplay; setChanged(); }
+
+    /** Apply server-validated config from an NBT (used by network handler). */
+    public void applyFromNbt(CompoundTag nbt) {
+        fromNbt(nbt);
+        setChanged();
+    }
+
+    /** Wire-format NBT used by SaveConfig/SyncAnchor payloads. */
+    public CompoundTag toNbt() {
+        CompoundTag nbt = new CompoundTag();
+        nbt.putString("url", url);
+        nbt.putInt("width", width);
+        nbt.putInt("height", height);
+        nbt.putString("facing", facing.getSerializedName());
+        nbt.putBoolean("loop", loop);
+        nbt.putFloat("volume", volume);
+        nbt.putBoolean("muted", muted);
+        nbt.putBoolean("autoplay", autoplay);
+        return nbt;
+    }
+
+    public void fromNbt(CompoundTag nbt) {
+        this.url = clampUrl(nbt.getStringOr("url", ""));
+        this.width = clamp(nbt.getIntOr("width", 1), 1, 32);
+        this.height = clamp(nbt.getIntOr("height", 1), 1, 32);
+        Direction d = directionFromName(nbt.getStringOr("facing", "north"));
+        this.facing = d == null ? Direction.NORTH : d;
+        this.loop = nbt.getBooleanOr("loop", true);
+        this.volume = Math.max(0F, Math.min(1F, nbt.getFloatOr("volume", 0.5F)));
+        this.muted = nbt.getBooleanOr("muted", false);
+        this.autoplay = nbt.getBooleanOr("autoplay", true);
+    }
+
+    @Override
+    protected void saveAdditional(ValueOutput out) {
+        super.saveAdditional(out);
+        out.putString("url", url);
+        out.putInt("width", width);
+        out.putInt("height", height);
+        out.putString("facing", facing.getSerializedName());
+        out.putBoolean("loop", loop);
+        out.putFloat("volume", volume);
+        out.putBoolean("muted", muted);
+        out.putBoolean("autoplay", autoplay);
+    }
+
+    @Override
+    protected void loadAdditional(ValueInput in) {
+        super.loadAdditional(in);
+        this.url = clampUrl(in.getStringOr("url", ""));
+        this.width = clamp(in.getIntOr("width", 1), 1, 32);
+        this.height = clamp(in.getIntOr("height", 1), 1, 32);
+        Direction d = directionFromName(in.getStringOr("facing", "north"));
+        this.facing = d == null ? Direction.NORTH : d;
+        this.loop = in.getBooleanOr("loop", true);
+        this.volume = Math.max(0F, Math.min(1F, in.getFloatOr("volume", 0.5F)));
+        this.muted = in.getBooleanOr("muted", false);
+        this.autoplay = in.getBooleanOr("autoplay", true);
+    }
+
+    private static Direction directionFromName(String name) {
+        if (name == null) return null;
+        for (Direction d : Direction.values()) {
+            if (d.getSerializedName().equalsIgnoreCase(name)) return d;
+        }
+        return null;
+    }
+
+    private static int clamp(int v, int lo, int hi) {
+        return Math.max(lo, Math.min(hi, v));
+    }
+
+    private static String clampUrl(String s) {
+        if (s == null) return "";
+        return s.length() > 256 ? s.substring(0, 256) : s;
     }
 }

src/main/java/com/ejclaw/videoplayer/client/gui/VideoConfigScreen.java

@@ -0,0 +1,139 @@
+package com.ejclaw.videoplayer.client.gui;
+
+import com.ejclaw.videoplayer.net.DeleteAnchorPayload;
+import com.ejclaw.videoplayer.net.SaveConfigPayload;
+import net.fabricmc.api.EnvType;
+import net.fabricmc.api.Environment;
+import net.fabricmc.fabric.api.client.networking.v1.ClientPlayNetworking;
+import net.minecraft.client.Minecraft;
+import net.minecraft.client.gui.components.AbstractSliderButton;
+import net.minecraft.client.gui.components.Button;
+import net.minecraft.client.gui.components.Checkbox;
+import net.minecraft.client.gui.components.EditBox;
+import net.minecraft.client.gui.screens.Screen;
+import net.minecraft.core.BlockPos;
+import net.minecraft.nbt.CompoundTag;
+import net.minecraft.network.chat.Component;
+
+/** SPEC §4.3 — anchor config GUI. Opened by S2C {@code OpenScreenPayload}. */
+@Environment(EnvType.CLIENT)
+public class VideoConfigScreen extends Screen {
+    private final BlockPos pos;
+    private final CompoundTag initial;
+
+    private EditBox urlField;
+    private EditBox widthField;
+    private EditBox heightField;
+    private Checkbox loopBox;
+    private Checkbox muteBox;
+    private Checkbox autoplayBox;
+    private VolumeSlider volumeSlider;
+
+    public VideoConfigScreen(BlockPos pos, CompoundTag data) {
+        super(Component.literal("Video Anchor"));
+        this.pos = pos;
+        this.initial = data;
+    }
+
+    @Override
+    protected void init() {
+        int cx = this.width / 2;
+        int y  = 40;
+
+        urlField = new EditBox(this.font, cx - 150, y, 300, 20, Component.literal("URL"));
+        urlField.setMaxLength(256);
+        urlField.setValue(initial.getStringOr("url", ""));
+        addRenderableWidget(urlField);
+        y += 30;
+
+        widthField  = new EditBox(this.font, cx - 150, y, 60, 20, Component.literal("W"));
+        widthField.setMaxLength(2);
+        widthField.setValue(Integer.toString(initial.getIntOr("width", 1)));
+        addRenderableWidget(widthField);
+
+        heightField = new EditBox(this.font, cx - 80, y, 60, 20, Component.literal("H"));
+        heightField.setMaxLength(2);
+        heightField.setValue(Integer.toString(initial.getIntOr("height", 1)));
+        addRenderableWidget(heightField);
+
+        volumeSlider = new VolumeSlider(cx - 10, y, 160, 20,
+            Math.max(0F, Math.min(1F, initial.getFloatOr("volume", 0.5F))));
+        addRenderableWidget(volumeSlider);
+        y += 30;
+
+        loopBox = Checkbox.builder(Component.literal("Loop"), this.font)
+            .pos(cx - 150, y).selected(initial.getBooleanOr("loop", true)).build();
+        addRenderableWidget(loopBox);
+
+        muteBox = Checkbox.builder(Component.literal("Mute"), this.font)
+            .pos(cx - 60, y).selected(initial.getBooleanOr("muted", false)).build();
+        addRenderableWidget(muteBox);
+
+        autoplayBox = Checkbox.builder(Component.literal("Autoplay"), this.font)
+            .pos(cx + 30, y).selected(initial.getBooleanOr("autoplay", true)).build();
+        addRenderableWidget(autoplayBox);
+        y += 36;
+
+        addRenderableWidget(Button.builder(Component.literal("Save"), b -> save())
+            .bounds(cx - 150, y, 90, 20).build());
+        addRenderableWidget(Button.builder(Component.literal("Cancel"), b -> onClose())
+            .bounds(cx - 45, y, 90, 20).build());
+        addRenderableWidget(Button.builder(Component.literal("Delete"), b -> delete())
+            .bounds(cx + 60, y, 90, 20).build());
+    }
+
+    private void save() {
+        CompoundTag out = new CompoundTag();
+        out.putString("url", urlField.getValue());
+        out.putInt("width",  parseInt(widthField.getValue(), 1));
+        out.putInt("height", parseInt(heightField.getValue(), 1));
+        out.putString("facing", initial.getStringOr("facing", "north"));
+        out.putBoolean("loop", loopBox.selected());
+        out.putFloat("volume", volumeSlider.getVolume());
+        out.putBoolean("muted", muteBox.selected());
+        out.putBoolean("autoplay", autoplayBox.selected());
+        ClientPlayNetworking.send(new SaveConfigPayload(pos, out));
+        onClose();
+    }
+
+    private void delete() {
+        ClientPlayNetworking.send(new DeleteAnchorPayload(pos));
+        onClose();
+    }
+
+    @Override
+    public boolean isPauseScreen() { return false; }
+
+    @Override
+    public void onClose() {
+        Minecraft mc = this.minecraft != null ? this.minecraft : Minecraft.getInstance();
+        if (mc != null) mc.setScreen(null);
+    }
+
+    private static int parseInt(String s, int dflt) {
+        try { return Integer.parseInt(s); } catch (Exception e) { return dflt; }
+    }
+
+    private static final class VolumeSlider extends AbstractSliderButton {
+        VolumeSlider(int x, int y, int w, int h, float initial) {
+            super(x, y, w, h, Component.literal("Volume: " + pct(initial)), initial);
+            updateMessage();
+        }
+
+        float getVolume() { return (float) this.value; }
+
+        @Override
+        protected void updateMessage() {
+            setMessage(Component.literal("Volume: " + pct((float) this.value)));
+        }
+
+        @Override
+        protected void applyValue() {
+            updateMessage();
+        }
+
+        private static int pct(float v) {
+            return Math.round(v * 100F);
+        }
+    }
+}

src/main/java/com/ejclaw/videoplayer/client/net/ClientNetworking.java

@@ -0,0 +1,35 @@
+package com.ejclaw.videoplayer.client.net;
+
+import com.ejclaw.videoplayer.block.VideoAnchorBlockEntity;
+import com.ejclaw.videoplayer.client.gui.VideoConfigScreen;
+import com.ejclaw.videoplayer.client.playback.VideoPlayback;
+import com.ejclaw.videoplayer.net.OpenScreenPayload;
+import com.ejclaw.videoplayer.net.SyncAnchorPayload;
+import net.fabricmc.api.EnvType;
+import net.fabricmc.api.Environment;
+import net.fabricmc.fabric.api.client.networking.v1.ClientPlayNetworking;
+import net.minecraft.client.Minecraft;
+
+/** Client-side S2C receivers for OpenScreen and SyncAnchor. */
+@Environment(EnvType.CLIENT)
+public final class ClientNetworking {
+    private ClientNetworking() {}
+
+    public static void register() {
+        ClientPlayNetworking.registerGlobalReceiver(OpenScreenPayload.TYPE, (payload, context) -> {
+            Minecraft mc = context.client();
+            mc.execute(() -> mc.setScreen(new VideoConfigScreen(payload.pos(), payload.data())));
+        });
+
+        ClientPlayNetworking.registerGlobalReceiver(SyncAnchorPayload.TYPE, (payload, context) -> {
+            Minecraft mc = context.client();
+            mc.execute(() -> {
+                if (mc.level == null) return;
+                if (mc.level.getBlockEntity(payload.pos()) instanceof VideoAnchorBlockEntity be) {
+                    be.applyFromNbt(payload.data());
+                    VideoPlayback.onConfigChanged(be);
+                }
+            });
+        });
+    }
+}

src/main/java/com/ejclaw/videoplayer/client/playback/JavaCvBackend.java

@@ -0,0 +1,252 @@
+package com.ejclaw.videoplayer.client.playback;
+
+import com.ejclaw.videoplayer.VideoPlayerMod;
+import net.fabricmc.api.EnvType;
+import net.fabricmc.api.Environment;
+
+import javax.sound.sampled.AudioFormat;
+import javax.sound.sampled.AudioSystem;
+import javax.sound.sampled.SourceDataLine;
+import java.lang.reflect.Field;
+import java.lang.reflect.Method;
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+import java.nio.ShortBuffer;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicReference;
+
+/**
+ * SPEC §5.3 — fallback mp4/http(s) backend driven by JavaCV's FFmpegFrameGrabber.
+ *
+ * <p>Video frames are decoded through {@code grab()}, audio samples are forced to interleaved
+ * signed 16-bit PCM ({@code AV_SAMPLE_FMT_S16}) and written to a {@link SourceDataLine} so that
+ * {@link #setVolume(float)} actually mutes / attenuates audible output. JavaCV is referenced
+ * entirely through reflection so that the mod jar stays loadable when the (large) JavaCV
+ * dependency isn't bundled — the backend just reports {@code !isReady()} until the runtime
+ * classpath contains {@code org.bytedeco.javacv.FFmpegFrameGrabber}.
+ */
+@Environment(EnvType.CLIENT)
+public class JavaCvBackend implements VideoBackend {
+    private static final String GRABBER_CLASS = "org.bytedeco.javacv.FFmpegFrameGrabber";
+    private static final String FRAME_CLASS   = "org.bytedeco.javacv.Frame";
+    private static final String CONVERTER_CLASS = "org.bytedeco.javacv.Java2DFrameConverter";
+    /** {@code AV_SAMPLE_FMT_S16} from {@code org.bytedeco.ffmpeg.global.avutil}. */
+    private static final int AV_SAMPLE_FMT_S16 = 1;
+
+    private final Object lock = new Object();
+    private Thread worker;
+    private final AtomicBoolean running = new AtomicBoolean(false);
+    private final AtomicBoolean paused  = new AtomicBoolean(false);
+    private final AtomicReference<ByteBuffer> latest = new AtomicReference<>();
+    private volatile int width = 0;
+    private volatile int height = 0;
+    private volatile float gain = 1.0F;
+    private volatile boolean loop = true;
+    private volatile boolean ready = false;
+    private volatile boolean closed = false;
+
+    @Override
+    public void play(String url, boolean loop) {
+        if (url == null || url.isEmpty()) return;
+        this.loop = loop;
+        synchronized (lock) {
+            stopWorker();
+            running.set(true);
+            paused.set(false);
+            worker = new Thread(() -> runLoop(url), "video_player-decode");
+            worker.setDaemon(true);
+            worker.start();
+        }
+    }
+
+    @Override
+    public void pause()  { paused.set(true); }
+    @Override
+    public void resume() { paused.set(false); }
+    @Override
+    public void setVolume(float g) { this.gain = Math.max(0F, Math.min(1F, g)); }
+    @Override
+    public boolean isReady() { return ready; }
+    @Override
+    public int videoWidth()  { return width; }
+    @Override
+    public int videoHeight() { return height; }
+
+    @Override
+    public ByteBuffer pollFrame() {
+        return latest.getAndSet(null);
+    }
+
+    @Override
+    public void close() {
+        closed = true;
+        stopWorker();
+    }
+
+    private void stopWorker() {
+        running.set(false);
+        Thread t = worker;
+        worker = null;
+        if (t != null) t.interrupt();
+        ready = false;
+    }
+
+    /** Pure-reflection decode loop. Silent fallback if JavaCV isn't present. */
+    private void runLoop(String url) {
+        Object grabber = null;
+        SourceDataLine audioLine = null;
+        try {
+            Class<?> grabberCls = Class.forName(GRABBER_CLASS);
+            grabber = grabberCls.getConstructor(String.class).newInstance(url);
+            Method start  = grabberCls.getMethod("start");
+            Method stop   = grabberCls.getMethod("stop");
+            Method grab   = grabberCls.getMethod("grab");
+            Method getW   = grabberCls.getMethod("getImageWidth");
+            Method getH   = grabberCls.getMethod("getImageHeight");
+            Method getSampleRate    = grabberCls.getMethod("getSampleRate");
+            Method getAudioChannels = grabberCls.getMethod("getAudioChannels");
+            Method setOpt = grabberCls.getMethod("setOption", String.class, String.class);
+            Method setSampleFormat  = grabberCls.getMethod("setSampleFormat", int.class);
+
+            // HTTP(S) tuning for streaming URLs (e.g. webm via Range / chunked transfer).
+            try { setOpt.invoke(grabber, "rw_timeout",         "10000000"); } catch (Throwable ignored) {}
+            try { setOpt.invoke(grabber, "timeout",            "10000000"); } catch (Throwable ignored) {}
+            try { setOpt.invoke(grabber, "reconnect",          "1");        } catch (Throwable ignored) {}
+            try { setOpt.invoke(grabber, "reconnect_streamed", "1");        } catch (Throwable ignored) {}
+            try { setOpt.invoke(grabber, "reconnect_at_eof",   "1");        } catch (Throwable ignored) {}
+            try { setOpt.invoke(grabber, "user_agent",
+                "video_player/" + com.ejclaw.videoplayer.VideoPlayerMod.MOD_ID); } catch (Throwable ignored) {}
+            // Force interleaved signed 16-bit PCM so the audio sink path is single-shape.
+            try { setSampleFormat.invoke(grabber, AV_SAMPLE_FMT_S16); } catch (Throwable ignored) {}
+
+            start.invoke(grabber);
+            this.width  = (int) getW.invoke(grabber);
+            this.height = (int) getH.invoke(grabber);
+            this.ready = (width > 0 && height > 0);
+
+            int sampleRate    = safeInt(getSampleRate, grabber);
+            int audioChannels = safeInt(getAudioChannels, grabber);
+            audioLine = openLine(sampleRate, audioChannels);
+
+            Class<?> frameCls    = Class.forName(FRAME_CLASS);
+            Field imageField     = frameCls.getField("image");
+            Field samplesField   = frameCls.getField("samples");
+            Class<?> convCls     = Class.forName(CONVERTER_CLASS);
+            Object converter     = convCls.getDeclaredConstructor().newInstance();
+            Method toImage       = convCls.getMethod("getBufferedImage", frameCls);
+
+            while (running.get() && !closed) {
+                if (paused.get()) { Thread.sleep(20); continue; }
+                Object frame = grab.invoke(grabber);
+                if (frame == null) {
+                    if (loop) {
+                        try { stop.invoke(grabber); } catch (Throwable ignored) {}
+                        try { start.invoke(grabber); } catch (Throwable ignored) {}
+                        continue;
+                    }
+                    break;
+                }
+
+                Object[] samples = (Object[]) samplesField.get(frame);
+                if (samples != null && samples.length > 0 && audioLine != null) {
+                    writeAudio(audioLine, samples, this.gain);
+                }
+
+                Object[] images = (Object[]) imageField.get(frame);
+                if (images != null && images.length > 0) {
+                    java.awt.image.BufferedImage img =
+                        (java.awt.image.BufferedImage) toImage.invoke(converter, frame);
+                    if (img != null) {
+                        ByteBuffer buf = toRgba(img);
+                        if (buf != null) latest.set(buf);
+                    }
+                }
+
+                // If we have an open audio line, SourceDataLine.write() blocks for backpressure
+                // and provides natural A/V pacing; otherwise tick ~60fps so we don't busy-loop.
+                if (audioLine == null) Thread.sleep(15);
+            }
+        } catch (ClassNotFoundException cnf) {
+            VideoPlayerMod.LOG.warn(
+                "[{}] JavaCV not on classpath — install org.bytedeco:javacv-platform (or javacv + ffmpeg natives)" +
+                " to enable video/audio playback. Anchor placeholder will remain visible.",
+                VideoPlayerMod.MOD_ID);
+        } catch (InterruptedException ie) {
+            Thread.currentThread().interrupt();
+        } catch (Throwable t) {
+            VideoPlayerMod.LOG.warn("[{}] JavaCV decode error: {}", VideoPlayerMod.MOD_ID, t.toString());
+        } finally {
+            ready = false;
+            if (audioLine != null) {
+                try { audioLine.drain(); } catch (Throwable ignored) {}
+                try { audioLine.stop();  } catch (Throwable ignored) {}
+                try { audioLine.close(); } catch (Throwable ignored) {}
+            }
+            if (grabber != null) {
+                try { grabber.getClass().getMethod("close").invoke(grabber); } catch (Throwable ignored) {}
+            }
+        }
+    }
+
+    /** Open a JavaSound output line for the stream's sample rate / channel count, or null. */
+    private static SourceDataLine openLine(int sampleRate, int channels) {
+        if (sampleRate <= 0 || channels <= 0) return null;
+        try {
+            AudioFormat fmt = new AudioFormat(sampleRate, 16, channels, true, false); // signed 16-bit LE
+            SourceDataLine line = AudioSystem.getSourceDataLine(fmt);
+            line.open(fmt);
+            line.start();
+            return line;
+        } catch (Throwable t) {
+            VideoPlayerMod.LOG.info("[{}] no audio sink ({} Hz x{}): {}",
+                VideoPlayerMod.MOD_ID, sampleRate, channels, t.toString());
+            return null;
+        }
+    }
+
+    /** Scale & write interleaved S16 PCM samples to the audio line. */
+    private static void writeAudio(SourceDataLine line, Object[] samples, float gain) {
+        if (!(samples[0] instanceof ShortBuffer sb)) return; // sample format forcing failed
+        int remaining = sb.remaining();
+        if (remaining <= 0) return;
+        byte[] pcm = new byte[remaining * 2];
+        int idx = 0;
+        if (gain >= 0.999F) {
+            while (sb.hasRemaining()) {
+                short s = sb.get();
+                pcm[idx++] = (byte) (s & 0xFF);
+                pcm[idx++] = (byte) ((s >> 8) & 0xFF);
+            }
+        } else if (gain <= 0F) {
+            // Mute: consume but emit silence so the line keeps cadence.
+            sb.position(sb.limit());
+        } else {
+            while (sb.hasRemaining()) {
+                int scaled = (int) (sb.get() * gain);
+                if (scaled >  32767) scaled =  32767;
+                if (scaled < -32768) scaled = -32768;
+                pcm[idx++] = (byte) (scaled & 0xFF);
+                pcm[idx++] = (byte) ((scaled >> 8) & 0xFF);
+            }
+        }
+        line.write(pcm, 0, pcm.length);
+    }
+
+    private static int safeInt(Method m, Object target) {
+        try { return (int) m.invoke(target); } catch (Throwable t) { return 0; }
+    }
+
+    private static ByteBuffer toRgba(java.awt.image.BufferedImage img) {
+        int w = img.getWidth(), h = img.getHeight();
+        int[] argb = img.getRGB(0, 0, w, h, null, 0, w);
+        ByteBuffer buf = ByteBuffer.allocateDirect(w * h * 4).order(ByteOrder.nativeOrder());
+        for (int p : argb) {
+            buf.put((byte) ((p >> 16) & 0xFF)); // R
+            buf.put((byte) ((p >>  8) & 0xFF)); // G
+            buf.put((byte) ( p        & 0xFF)); // B
+            buf.put((byte) ((p >> 24) & 0xFF)); // A
+        }
+        buf.flip();
+        return buf;
+    }
+}

src/main/java/com/ejclaw/videoplayer/client/playback/VideoBackend.java

@@ -0,0 +1,30 @@
+package com.ejclaw.videoplayer.client.playback;
+
+import net.fabricmc.api.EnvType;
+import net.fabricmc.api.Environment;
+
+import java.nio.ByteBuffer;
+
+/**
+ * SPEC §5.3 — minimal playback backend abstraction. Implementations: WatermediaBackend (preferred,
+ * when v2 supports the target MC version) and JavaCvBackend (fallback).
+ */
+@Environment(EnvType.CLIENT)
+public interface VideoBackend {
+    void play(String url, boolean loop);
+    void pause();
+    void resume();
+    void setVolume(float gain);
+
+    boolean isReady();
+    int videoWidth();
+    int videoHeight();
+
+    /**
+     * Poll a new decoded RGBA frame if one is ready.
+     * @return the frame buffer (capacity = w*h*4) or {@code null} if no new frame is ready.
+     */
+    ByteBuffer pollFrame();
+
+    void close();
+}

src/main/java/com/ejclaw/videoplayer/client/playback/VideoPlayback.java

@@ -0,0 +1,203 @@
+package com.ejclaw.videoplayer.client.playback;
+
+import com.ejclaw.videoplayer.VideoPlayerMod;
+import com.ejclaw.videoplayer.block.VideoAnchorBlockEntity;
+import com.mojang.blaze3d.platform.NativeImage;
+import net.fabricmc.api.EnvType;
+import net.fabricmc.api.Environment;
+import net.minecraft.client.Minecraft;
+import net.minecraft.client.renderer.texture.DynamicTexture;
+import net.minecraft.core.BlockPos;
+import net.minecraft.resources.Identifier;
+
+import java.nio.ByteBuffer;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Iterator;
+import java.util.Map;
+import java.util.Set;
+
+/**
+ * SPEC §5 — per-anchor playback registry. Maps {@link BlockPos} → ({@link VideoBackend} +
+ * a {@link DynamicTexture} surface registered under a unique {@link Identifier}). The renderer
+ * reads {@link #currentTexture(BlockPos)} and binds it to the quad. {@link #tick()} pumps
+ * decoded RGBA frames into the texture.
+ *
+ * <p>When no backend is available on the classpath (e.g. JavaCV jar not installed by the
+ * user), the texture stays at its initial placeholder pattern, so the anchor's screen quad
+ * still renders as a visible surface.
+ */
+@Environment(EnvType.CLIENT)
+public final class VideoPlayback {
+    private VideoPlayback() {}
+
+    private static final int PLACEHOLDER_SIZE = 32;
+    private static final Map<BlockPos, Entry> ENTRIES = new HashMap<>();
+
+    /**
+     * Ensure a playback entry exists for this anchor and return its texture identifier.
+     * Creates a backend + dynamic texture on first call. Returns {@code null} only if the
+     * URL is empty or autoplay is off.
+     */
+    public static Identifier getOrStart(VideoAnchorBlockEntity be) {
+        BlockPos pos = be.getBlockPos();
+        Entry e = ENTRIES.get(pos);
+
+        if (be.getUrl().isEmpty() || !be.isAutoplay()) {
+            if (e != null) {
+                stop(pos);
+            }
+            return null;
+        }
+
+        if (e != null && e.url.equals(be.getUrl())) {
+            return e.id;
+        }
+        if (e != null) {
+            stop(pos);
+        }
+
+        VideoBackend backend = WatermediaProbe.isAvailable() ? new WatermediaBackend() : new JavaCvBackend();
+        backend.play(be.getUrl(), be.isLoop());
+        backend.setVolume(be.isMuted() ? 0F : be.getVolume());
+
+        Entry created = new Entry(be.getUrl(), backend);
+        ENTRIES.put(pos, created);
+        return created.id;
+    }
+
+    public static Identifier currentTexture(BlockPos pos) {
+        Entry e = ENTRIES.get(pos);
+        return e == null ? null : e.id;
+    }
+
+    public static void stop(BlockPos pos) {
+        Entry e = ENTRIES.remove(pos);
+        if (e != null) e.close();
+    }
+
+    public static void onConfigChanged(VideoAnchorBlockEntity be) {
+        if (be == null) return;
+        Entry e = ENTRIES.get(be.getBlockPos());
+        if (e == null) return;
+        if (!e.url.equals(be.getUrl())) {
+            stop(be.getBlockPos());
+            return;
+        }
+        e.backend.setVolume(be.isMuted() ? 0F : be.getVolume());
+    }
+
+    /** Called every client tick to upload new frames into the GPU texture. */
+    public static void tick() {
+        if (Minecraft.getInstance() == null) return;
+        Iterator<Map.Entry<BlockPos, Entry>> it = ENTRIES.entrySet().iterator();
+        while (it.hasNext()) {
+            Map.Entry<BlockPos, Entry> me = it.next();
+            Entry e = me.getValue();
+            if (!e.backend.isReady()) continue;
+            ByteBuffer buf = e.backend.pollFrame();
+            if (buf == null) continue;
+            try {
+                e.upload(buf);
+            } catch (Throwable t) {
+                VideoPlayerMod.LOG.warn("[{}] texture upload failed: {}", VideoPlayerMod.MOD_ID, t.toString());
+                e.close();
+                it.remove();
+            }
+        }
+    }
+
+    public static Set<BlockPos> activePositions() {
+        return new HashSet<>(ENTRIES.keySet());
+    }
+
+    public static void setGain(BlockPos pos, float gain) {
+        Entry e = ENTRIES.get(pos);
+        if (e != null) e.backend.setVolume(gain);
+    }
+
+    public static void stopAll() {
+        for (Entry e : ENTRIES.values()) e.close();
+        ENTRIES.clear();
+    }
+
+    /** Per-anchor playback state. */
+    private static final class Entry {
+        final String url;
+        final VideoBackend backend;
+        final Identifier id;
+        DynamicTexture texture;
+        int texW = 0, texH = 0;
+        boolean registered = false;
+
+        Entry(String url, VideoBackend backend) {
+            this.url = url;
+            this.backend = backend;
+            String tag = Integer.toHexString(System.identityHashCode(this));
+            this.id = Identifier.fromNamespaceAndPath(VideoPlayerMod.MOD_ID, "dynamic/" + tag);
+            ensureTexture(PLACEHOLDER_SIZE, PLACEHOLDER_SIZE, true);
+        }
+
+        /** Allocate or resize the dynamic texture, registering it on first allocation. */
+        private void ensureTexture(int w, int h, boolean fillPlaceholder) {
+            if (texture != null && w == texW && h == texH) return;
+            if (texture != null) texture.close();
+            NativeImage img = new NativeImage(w, h, false);
+            if (fillPlaceholder) {
+                fillPlaceholder(img, w, h);
+            }
+            texture = new DynamicTexture(() -> "video_player:" + id, img);
+            texW = w;
+            texH = h;
+            Minecraft mc = Minecraft.getInstance();
+            if (mc != null) {
+                mc.getTextureManager().register(id, texture);
+                registered = true;
+            }
+            texture.upload();
+        }
+
+        /** Dark gray surface with a thin border — visible "screen" until first frame arrives. */
+        private static void fillPlaceholder(NativeImage img, int w, int h) {
+            // ABGR int. 0xAABBGGRR.
+            int body   = 0xFF202020; // dark gray
+            int border = 0xFF505050;
+            for (int y = 0; y < h; y++) {
+                for (int x = 0; x < w; x++) {
+                    boolean isEdge = (x == 0 || y == 0 || x == w - 1 || y == h - 1);
+                    img.setPixelABGR(x, y, isEdge ? border : body);
+                }
+            }
+        }
+
+        /** Copy an incoming RGBA byte buffer into the texture, resizing if dimensions changed. */
+        void upload(ByteBuffer rgba) {
+            int w = backend.videoWidth();
+            int h = backend.videoHeight();
+            if (w <= 0 || h <= 0) return;
+            ensureTexture(w, h, false);
+            NativeImage img = texture.getPixels();
+            if (img == null) return;
+
+            int pixels = w * h;
+            for (int i = 0; i < pixels; i++) {
+                int r = rgba.get() & 0xFF;
+                int g = rgba.get() & 0xFF;
+                int b = rgba.get() & 0xFF;
+                int a = rgba.get() & 0xFF;
+                int abgr = (a << 24) | (b << 16) | (g << 8) | r;
+                img.setPixelABGR(i % w, i / w, abgr);
+            }
+            texture.upload();
+        }
+
+        void close() {
+            try { backend.close(); } catch (Throwable ignored) {}
+            if (texture != null) {
+                try { texture.close(); } catch (Throwable ignored) {}
+                texture = null;
+            }
+            // texture manager keeps the registration; the texture itself is closed.
+        }
+    }
+}

src/main/java/com/ejclaw/videoplayer/client/playback/WatermediaBackend.java

@@ -0,0 +1,50 @@
+package com.ejclaw.videoplayer.client.playback;
+
+import com.ejclaw.videoplayer.VideoPlayerMod;
+import net.fabricmc.api.EnvType;
+import net.fabricmc.api.Environment;
+
+import java.nio.ByteBuffer;
+
+/**
+ * SPEC §5.3 / §5.4 — WaterMedia v2 backend. Reflection-only so the mod jar stays clean of
+ * compile-time WaterMedia dependencies. Until a v2 build supports 1.21.6+ this returns
+ * {@code !isReady()} and {@link WatermediaProbe} reports unavailable, so callers fall through
+ * to {@link JavaCvBackend}.
+ */
+@Environment(EnvType.CLIENT)
+public class WatermediaBackend implements VideoBackend {
+    private volatile boolean ready = false;
+    private volatile int width = 0;
+    private volatile int height = 0;
+    private volatile float gain = 1.0F;
+    private Object player;
+
+    @Override
+    public void play(String url, boolean loop) {
+        if (!WatermediaProbe.isAvailable()) {
+            VideoPlayerMod.LOG.debug("[{}] WatermediaBackend.play called but probe says unavailable",
+                VideoPlayerMod.MOD_ID);
+            return;
+        }
+        // Reflection construction skipped — only reachable when WaterMedia v2 ships for the target MC.
+    }
+
+    @Override public void pause() {}
+    @Override public void resume() {}
+    @Override public void setVolume(float g) { this.gain = Math.max(0F, Math.min(1F, g)); }
+    @Override public boolean isReady() { return ready; }
+    @Override public int videoWidth()  { return width; }
+    @Override public int videoHeight() { return height; }
+
+    @Override
+    public ByteBuffer pollFrame() {
+        return null; // no frames until v2 is wired up
+    }
+
+    @Override
+    public void close() {
+        ready = false;
+        player = null;
+    }
+}

src/main/java/com/ejclaw/videoplayer/client/playback/WatermediaProbe.java

@@ -0,0 +1,35 @@
+package com.ejclaw.videoplayer.client.playback;
+
+import com.ejclaw.videoplayer.VideoPlayerMod;
+import net.fabricmc.api.EnvType;
+import net.fabricmc.api.Environment;
+
+/**
+ * SPEC §5.4 — Reflection-only check for whether WaterMedia v2 is present and usable on this MC.
+ * As of 1.21.6+ WaterMedia v2 has no Yarn-mapped artifact, so this always reports false; we keep the
+ * shape so the mod will auto-prefer WaterMedia when a future build adds it.
+ */
+@Environment(EnvType.CLIENT)
+public final class WatermediaProbe {
+    private WatermediaProbe() {}
+
+    private static final Boolean CACHED = compute();
+
+    public static boolean isAvailable() {
+        return CACHED;
+    }
+
+    private static boolean compute() {
+        try {
+            Class.forName("me.srrapero720.watermedia.api.WaterMediaAPI", false,
+                WatermediaProbe.class.getClassLoader());
+            VideoPlayerMod.LOG.info("[{}] WaterMedia v2 detected", VideoPlayerMod.MOD_ID);
+            return true;
+        } catch (ClassNotFoundException e) {
+            return false;
+        } catch (Throwable t) {
+            VideoPlayerMod.LOG.warn("[{}] WaterMedia probe failed: {}", VideoPlayerMod.MOD_ID, t.toString());
+            return false;
+        }
+    }
+}

src/main/java/com/ejclaw/videoplayer/client/render/VideoAnchorRenderer.java

@@ -0,0 +1,139 @@
+package com.ejclaw.videoplayer.client.render;
+
+import com.ejclaw.videoplayer.block.VideoAnchorBlockEntity;
+import com.ejclaw.videoplayer.client.playback.VideoPlayback;
+import com.mojang.blaze3d.vertex.PoseStack;
+import com.mojang.math.Axis;
+import net.fabricmc.api.EnvType;
+import net.fabricmc.api.Environment;
+import net.minecraft.client.renderer.SubmitNodeCollector;
+import net.minecraft.client.renderer.blockentity.BlockEntityRenderer;
+import net.minecraft.client.renderer.blockentity.BlockEntityRendererProvider;
+import net.minecraft.client.renderer.blockentity.state.BlockEntityRenderState;
+import net.minecraft.client.renderer.feature.ModelFeatureRenderer;
+import net.minecraft.client.renderer.rendertype.RenderType;
+import net.minecraft.client.renderer.rendertype.RenderTypes;
+import net.minecraft.client.renderer.state.level.CameraRenderState;
+import net.minecraft.core.Direction;
+import net.minecraft.resources.Identifier;
+import net.minecraft.world.phys.Vec3;
+import org.joml.Matrix4f;
+
+/**
+ * Draws the video as a textured quad <em>on the surface of the block the user clicked</em>.
+ *
+ * <p>The anchor BE lives in the air block adjacent to the clicked wall. Its {@code facing}
+ * field is the surface normal of the wall (= the {@link Direction} the player clicked). The
+ * quad is rotated so its normal aligns with that direction and shifted so it sits flush against
+ * the wall surface, with a tiny outward offset to avoid z-fighting.
+ */
+@Environment(EnvType.CLIENT)
+public class VideoAnchorRenderer implements BlockEntityRenderer<VideoAnchorBlockEntity, VideoAnchorRenderer.State> {
+
+    /** Tiny outward offset so the quad doesn't z-fight with the wall. */
+    private static final float SURFACE_EPSILON = 0.001F;
+
+    public VideoAnchorRenderer(BlockEntityRendererProvider.Context ctx) {
+        // no-op
+    }
+
+    @Override
+    public State createRenderState() {
+        return new State();
+    }
+
+    @Override
+    public void extractRenderState(VideoAnchorBlockEntity be, State state, float partialTick,
+                                   Vec3 cameraPos, ModelFeatureRenderer.CrumblingOverlay crumbling) {
+        BlockEntityRenderState.extractBase(be, state, crumbling);
+        state.width = be.getWidth();
+        state.height = be.getHeight();
+        state.facing = be.getFacing();
+        state.textureId = VideoPlayback.getOrStart(be);
+    }
+
+    @Override
+    public void submit(State state, PoseStack pose, SubmitNodeCollector collector, CameraRenderState camera) {
+        Identifier tex = state.textureId;
+        if (tex == null) return; // url empty or autoplay off — nothing to draw
+
+        final float w = state.width;
+        final float h = state.height;
+        final int light = state.lightCoords;
+        final Direction f = state.facing == null ? Direction.NORTH : state.facing;
+
+        pose.pushPose();
+        // 1) Move to the anchor block's center.
+        pose.translate(0.5F, 0.5F, 0.5F);
+        // 2) Rotate local +Z to align with the wall's outward normal.
+        applyFaceRotation(pose, f);
+        // 3) Place the quad's local origin (0,0) at the bottom-left corner of the anchor block's
+        //    wall face, so the clicked block becomes the lower-left and the video grows up & right.
+        //    Push it onto the wall surface (-0.5 along local +Z, the outward normal) plus a tiny
+        //    epsilon outward so the quad doesn't z-fight with the wall.
+        pose.translate(-0.5F, -0.5F, -0.5F + SURFACE_EPSILON);
+
+        final Matrix4f mat = new Matrix4f(pose.last().pose());
+        RenderType rt = RenderTypes.entityCutout(tex);
+        collector.submitCustomGeometry(pose, rt, (poseUnused, vc) -> {
+            // Front face (visible from outside, looking back at the wall)
+            emit(vc, mat, 0F, 0F, 0F, 0F, 1F, light);
+            emit(vc, mat, w,  0F, 0F, 1F, 1F, light);
+            emit(vc, mat, w,  h,  0F, 1F, 0F, light);
+            emit(vc, mat, 0F, h,  0F, 0F, 0F, light);
+            // Back face (in case the player ends up on the other side, e.g. clipping into the wall)
+            emit(vc, mat, 0F, h,  0F, 0F, 0F, light);
+            emit(vc, mat, w,  h,  0F, 1F, 0F, light);
+            emit(vc, mat, w,  0F, 0F, 1F, 1F, light);
+            emit(vc, mat, 0F, 0F, 0F, 0F, 1F, light);
+        });
+
+        pose.popPose();
+    }
+
+    /**
+     * Rotate so local +Z (the quad's outward normal in its base orientation) becomes world {@code f},
+     * with local +X mapped to the natural "right" direction the player sees when looking at the face.
+     * Derivation: for each face {@code f}, pick the rotation that maps local +Z → f, +Y → world up
+     * (or a sensible substitute for top/bottom), so the quad lies flush against the wall, oriented
+     * the way the player intuits.
+     */
+    private static void applyFaceRotation(PoseStack pose, Direction f) {
+        switch (f) {
+            case SOUTH -> { /* identity: local +Z = world +Z (south). +X = east, +Y = up. */ }
+            case NORTH -> pose.mulPose(Axis.YP.rotationDegrees(180F));  // +Z → -Z, +X → -X (west)
+            case EAST  -> pose.mulPose(Axis.YP.rotationDegrees(90F));   // +Z → +X, +X → -Z (north)
+            case WEST  -> pose.mulPose(Axis.YP.rotationDegrees(-90F));  // +Z → -X, +X → +Z (south)
+            case UP    -> pose.mulPose(Axis.XP.rotationDegrees(-90F));  // +Z → +Y, +Y → -Z (north)
+            case DOWN  -> pose.mulPose(Axis.XP.rotationDegrees(90F));   // +Z → -Y, +Y → +Z (south)
+        }
+    }
+
+    private static void emit(com.mojang.blaze3d.vertex.VertexConsumer vc, Matrix4f mat,
+                             float x, float y, float z, float u, float v, int light) {
+        vc.addVertex(mat, x, y, z)
+          .setColor(255, 255, 255, 255)
+          .setUv(u, v)
+          .setOverlay(net.minecraft.client.renderer.texture.OverlayTexture.NO_OVERLAY)
+          .setLight(light)
+          .setNormal(0F, 0F, 1F);
+    }
+
+    @Override
+    public boolean shouldRenderOffScreen() {
+        return true;
+    }
+
+    @Override
+    public int getViewDistance() {
+        return 128;
+    }
+
+    /** Per-frame render data extracted from the BE. */
+    public static final class State extends BlockEntityRenderState {
+        public Identifier textureId;
+        public int width = 1;
+        public int height = 1;
+        public Direction facing = Direction.NORTH;
+    }
+}

src/main/java/com/ejclaw/videoplayer/command/VideoDeleteCommand.java

@@ -0,0 +1,46 @@
+package com.ejclaw.videoplayer.command;
+
+import com.ejclaw.videoplayer.block.VideoAnchorBlockEntity;
+import com.mojang.brigadier.CommandDispatcher;
+import com.mojang.brigadier.exceptions.CommandSyntaxException;
+import net.minecraft.commands.CommandSourceStack;
+import net.minecraft.commands.Commands;
+import net.minecraft.commands.arguments.coordinates.BlockPosArgument;
+import net.minecraft.core.BlockPos;
+import net.minecraft.network.chat.Component;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.server.permissions.Permissions;
+import net.minecraft.world.level.block.Block;
+import net.minecraft.world.level.block.Blocks;
+
+/** SPEC §4.5.1 — {@code /videoDelete <pos>} */
+public final class VideoDeleteCommand {
+    private VideoDeleteCommand() {}
+
+    public static void register(CommandDispatcher<CommandSourceStack> dispatcher) {
+        dispatcher.register(build("videoDelete"));
+        dispatcher.register(build("videodelete"));
+    }
+
+    private static com.mojang.brigadier.builder.LiteralArgumentBuilder<CommandSourceStack>
+    build(String name) {
+        return Commands.literal(name)
+            .requires(s -> s.permissions().hasPermission(Permissions.COMMANDS_GAMEMASTER))
+            .then(Commands.argument("pos", BlockPosArgument.blockPos())
+                .executes(VideoDeleteCommand::run));
+    }
+
+    private static int run(com.mojang.brigadier.context.CommandContext<CommandSourceStack> ctx)
+            throws CommandSyntaxException {
+        CommandSourceStack src = ctx.getSource();
+        ServerLevel level = src.getLevel();
+        BlockPos pos = BlockPosArgument.getLoadedBlockPos(ctx, "pos");
+        if (!(level.getBlockEntity(pos) instanceof VideoAnchorBlockEntity)) {
+            src.sendFailure(Component.literal("no anchor at that position"));
+            return 0;
+        }
+        level.setBlock(pos, Blocks.AIR.defaultBlockState(), Block.UPDATE_ALL);
+        src.sendSuccess(() -> Component.literal("anchor deleted at " + pos.toShortString()), true);
+        return 1;
+    }
+}

src/main/java/com/ejclaw/videoplayer/command/VideoMuteCommand.java

@@ -0,0 +1,62 @@
+package com.ejclaw.videoplayer.command;
+
+import com.ejclaw.videoplayer.block.VideoAnchorBlockEntity;
+import com.ejclaw.videoplayer.net.SyncAnchorPayload;
+import com.mojang.brigadier.CommandDispatcher;
+import com.mojang.brigadier.arguments.StringArgumentType;
+import com.mojang.brigadier.exceptions.CommandSyntaxException;
+import net.fabricmc.fabric.api.networking.v1.PlayerLookup;
+import net.fabricmc.fabric.api.networking.v1.ServerPlayNetworking;
+import net.minecraft.commands.CommandSourceStack;
+import net.minecraft.commands.Commands;
+import net.minecraft.commands.arguments.coordinates.BlockPosArgument;
+import net.minecraft.core.BlockPos;
+import net.minecraft.network.chat.Component;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.server.permissions.Permissions;
+
+/** SPEC §4.5.1 — {@code /videoMute <pos> <on|off>} */
+public final class VideoMuteCommand {
+    private VideoMuteCommand() {}
+
+    public static void register(CommandDispatcher<CommandSourceStack> dispatcher) {
+        dispatcher.register(build("videoMute"));
+        dispatcher.register(build("videomute"));
+    }
+
+    private static com.mojang.brigadier.builder.LiteralArgumentBuilder<CommandSourceStack>
+    build(String name) {
+        return Commands.literal(name)
+            .requires(s -> s.permissions().hasPermission(Permissions.COMMANDS_GAMEMASTER))
+            .then(Commands.argument("pos", BlockPosArgument.blockPos())
+                .then(Commands.argument("state", StringArgumentType.word())
+                    .executes(VideoMuteCommand::run)));
+    }
+
+    private static int run(com.mojang.brigadier.context.CommandContext<CommandSourceStack> ctx)
+            throws CommandSyntaxException {
+        CommandSourceStack src = ctx.getSource();
+        ServerLevel level = src.getLevel();
+        BlockPos pos = BlockPosArgument.getLoadedBlockPos(ctx, "pos");
+        String state = StringArgumentType.getString(ctx, "state").toLowerCase();
+        boolean muted;
+        if ("on".equals(state) || "true".equals(state))      muted = true;
+        else if ("off".equals(state) || "false".equals(state)) muted = false;
+        else {
+            src.sendFailure(Component.literal("state must be on/off"));
+            return 0;
+        }
+        if (!(level.getBlockEntity(pos) instanceof VideoAnchorBlockEntity be)) {
+            src.sendFailure(Component.literal("no anchor at that position"));
+            return 0;
+        }
+        be.setMuted(muted);
+        for (ServerPlayer p : PlayerLookup.tracking(level, pos)) {
+            ServerPlayNetworking.send(p, new SyncAnchorPayload(pos, be.toNbt()));
+        }
+        final boolean mFinal = muted;
+        src.sendSuccess(() -> Component.literal("anchor " + (mFinal ? "muted" : "unmuted")), true);
+        return 1;
+    }
+}

src/main/java/com/ejclaw/videoplayer/command/VideoPlaceCommand.java

@@ -0,0 +1,90 @@
+package com.ejclaw.videoplayer.command;
+
+import com.ejclaw.videoplayer.block.VideoAnchorBlockEntity;
+import com.ejclaw.videoplayer.net.SyncAnchorPayload;
+import com.ejclaw.videoplayer.registry.VideoPlayerBlocks;
+import com.mojang.brigadier.CommandDispatcher;
+import com.mojang.brigadier.arguments.IntegerArgumentType;
+import com.mojang.brigadier.arguments.StringArgumentType;
+import com.mojang.brigadier.exceptions.CommandSyntaxException;
+import net.fabricmc.fabric.api.networking.v1.PlayerLookup;
+import net.fabricmc.fabric.api.networking.v1.ServerPlayNetworking;
+import net.minecraft.commands.CommandSourceStack;
+import net.minecraft.commands.Commands;
+import net.minecraft.commands.arguments.coordinates.BlockPosArgument;
+import net.minecraft.core.BlockPos;
+import net.minecraft.core.Direction;
+import net.minecraft.nbt.CompoundTag;
+import net.minecraft.network.chat.Component;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.server.permissions.Permissions;
+import net.minecraft.world.level.block.Block;
+
+/** SPEC §4.5.1 — {@code /videoPlace <pos> <facing> <width> <height> <url>} */
+public final class VideoPlaceCommand {
+    private VideoPlaceCommand() {}
+
+    public static void register(CommandDispatcher<CommandSourceStack> dispatcher) {
+        dispatcher.register(build("videoPlace"));
+        dispatcher.register(build("videoplace"));
+    }
+
+    private static com.mojang.brigadier.builder.LiteralArgumentBuilder<CommandSourceStack>
+    build(String name) {
+        return Commands.literal(name)
+            .requires(s -> s.permissions().hasPermission(Permissions.COMMANDS_GAMEMASTER))
+            .then(Commands.argument("pos", BlockPosArgument.blockPos())
+                .then(Commands.argument("facing", StringArgumentType.word())
+                    .then(Commands.argument("width", IntegerArgumentType.integer(1, 32))
+                        .then(Commands.argument("height", IntegerArgumentType.integer(1, 32))
+                            .then(Commands.argument("url", StringArgumentType.greedyString())
+                                .executes(VideoPlaceCommand::run))))));
+    }
+
+    private static int run(com.mojang.brigadier.context.CommandContext<CommandSourceStack> ctx)
+            throws CommandSyntaxException {
+        CommandSourceStack src = ctx.getSource();
+        ServerLevel level = src.getLevel();
+        BlockPos pos = BlockPosArgument.getLoadedBlockPos(ctx, "pos");
+        Direction facing = directionFromName(StringArgumentType.getString(ctx, "facing"));
+        if (facing == null) {
+            src.sendFailure(Component.literal("facing must be north/south/east/west/up/down"));
+            return 0;
+        }
+        int width  = IntegerArgumentType.getInteger(ctx, "width");
+        int height = IntegerArgumentType.getInteger(ctx, "height");
+        String url = StringArgumentType.getString(ctx, "url").trim();
+        if (!url.isEmpty() && !(url.startsWith("http://") || url.startsWith("https://"))) {
+            src.sendFailure(Component.literal("url must be http:// or https:// (or empty)"));
+            return 0;
+        }
+        if (url.length() > 256) url = url.substring(0, 256);
+
+        level.setBlock(pos, VideoPlayerBlocks.VIDEO_ANCHOR.defaultBlockState(), Block.UPDATE_ALL);
+        if (!(level.getBlockEntity(pos) instanceof VideoAnchorBlockEntity be)) {
+            src.sendFailure(Component.literal("failed to place anchor"));
+            return 0;
+        }
+        be.setFacing(facing);
+        be.setWidth(width);
+        be.setHeight(height);
+        be.setUrl(url);
+
+        CompoundTag nbt = be.toNbt();
+        for (ServerPlayer p : PlayerLookup.tracking(level, pos)) {
+            ServerPlayNetworking.send(p, new SyncAnchorPayload(pos, nbt));
+        }
+        final BlockPos fp = pos;
+        src.sendSuccess(() -> Component.literal("anchor placed at " + fp.toShortString()), true);
+        return 1;
+    }
+
+    private static Direction directionFromName(String name) {
+        if (name == null) return null;
+        for (Direction d : Direction.values()) {
+            if (d.getSerializedName().equalsIgnoreCase(name)) return d;
+        }
+        return null;
+    }
+}

src/main/java/com/ejclaw/videoplayer/command/VideoStickCommand.java

@@ -2,35 +2,35 @@ package com.ejclaw.videoplayer.command;
 
 import com.ejclaw.videoplayer.registry.VideoPlayerItems;
 import com.mojang.brigadier.CommandDispatcher;
-import net.minecraft.item.ItemStack;
+import net.minecraft.commands.CommandSourceStack;
-import net.minecraft.server.command.CommandManager;
+import net.minecraft.commands.Commands;
-import net.minecraft.server.command.ServerCommandSource;
+import net.minecraft.network.chat.Component;
-import net.minecraft.server.network.ServerPlayerEntity;
+import net.minecraft.server.level.ServerPlayer;
-import net.minecraft.text.Text;
+import net.minecraft.world.item.ItemStack;
 
 public final class VideoStickCommand {
     private VideoStickCommand() {}
 
-    public static void register(CommandDispatcher<ServerCommandSource> dispatcher) {
+    public static void register(CommandDispatcher<CommandSourceStack> dispatcher) {
-        dispatcher.register(CommandManager.literal("videoStick")
+        dispatcher.register(Commands.literal("videoStick")
             .executes(ctx -> run(ctx.getSource())));
         // Lowercase alias — Brigadier is case-sensitive.
-        dispatcher.register(CommandManager.literal("videostick")
+        dispatcher.register(Commands.literal("videostick")
             .executes(ctx -> run(ctx.getSource())));
     }
 
-    private static int run(ServerCommandSource source) {
+    private static int run(CommandSourceStack source) {
-        ServerPlayerEntity player = source.getPlayer();
+        ServerPlayer player = source.getPlayer();
         if (player == null) {
-            source.sendError(Text.literal("플레이어만 이 명령을 사용할 수 있습니다."));
+            source.sendFailure(Component.literal("플레이어만 이 명령을 사용할 수 있습니다."));
             return 0;
         }
         ItemStack stack = new ItemStack(VideoPlayerItems.VIDEO_STICK);
-        boolean inserted = player.getInventory().insertStack(stack);
+        boolean inserted = player.getInventory().add(stack);
         if (!inserted || !stack.isEmpty()) {
-            player.dropItem(stack, false);
+            player.drop(stack, false, false);
         }
-        source.sendFeedback(() -> Text.literal("비디오 스틱을 지급했습니다."), false);
+        source.sendSuccess(() -> Component.literal("비디오 스틱을 지급했습니다."), false);
         return 1;
     }
 }

src/main/java/com/ejclaw/videoplayer/item/VideoStickItem.java

@@ -1,12 +1,71 @@
 package com.ejclaw.videoplayer.item;
 
-import net.minecraft.item.Item;
+import com.ejclaw.videoplayer.block.VideoAnchorBlockEntity;
+import com.ejclaw.videoplayer.net.OpenScreenPayload;
+import com.ejclaw.videoplayer.registry.VideoPlayerBlocks;
+import net.fabricmc.fabric.api.networking.v1.ServerPlayNetworking;
+import net.minecraft.core.BlockPos;
+import net.minecraft.core.Direction;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.world.InteractionResult;
+import net.minecraft.world.entity.player.Player;
+import net.minecraft.world.item.Item;
+import net.minecraft.world.item.context.UseOnContext;
+import net.minecraft.world.level.Level;
+import net.minecraft.world.level.block.Block;
+import net.minecraft.world.level.block.state.BlockState;
 
 /**
- * M1: registered placeholder. Right/left-click handlers land in M4–M5.
+ * Right-click a block's face with the video stick:
+ * <ul>
+ *   <li>If a video anchor already exists in the adjacent air (= an anchor already drawn on this
+ *       face), reopen its config GUI.</li>
+ *   <li>Otherwise place an invisible anchor in the adjacent air block, set its facing to the
+ *       clicked face direction (so the renderer draws the quad flush against this face), and
+ *       open the config GUI.</li>
+ * </ul>
+ * The anchor block itself is invisible / non-collidable, so visually no new block appears —
+ * the video just shows up on the face the user clicked.
  */
 public class VideoStickItem extends Item {
-    public VideoStickItem(Settings settings) {
+    public VideoStickItem(Properties properties) {
-        super(settings);
+        super(properties);
+    }
+
+    @Override
+    public InteractionResult useOn(UseOnContext ctx) {
+        Level level = ctx.getLevel();
+        if (level.isClientSide()) {
+            return InteractionResult.SUCCESS;
+        }
+        if (!(level instanceof ServerLevel sl)) return InteractionResult.PASS;
+        Player player = ctx.getPlayer();
+        if (!(player instanceof ServerPlayer sp)) return InteractionResult.PASS;
+
+        BlockPos hit = ctx.getClickedPos();
+        Direction face = ctx.getClickedFace();
+        BlockPos anchorPos = hit.relative(face);
+
+        // Existing anchor on this face → reopen edit GUI.
+        if (sl.getBlockEntity(anchorPos) instanceof VideoAnchorBlockEntity existing) {
+            ServerPlayNetworking.send(sp, new OpenScreenPayload(anchorPos, existing.toNbt()));
+            return InteractionResult.SUCCESS;
+        }
+
+        // Need an empty / replaceable space in front of the clicked face.
+        BlockState there = sl.getBlockState(anchorPos);
+        if (!there.canBeReplaced()) return InteractionResult.PASS;
+
+        Block anchor = VideoPlayerBlocks.VIDEO_ANCHOR;
+        sl.setBlock(anchorPos, anchor.defaultBlockState(), Block.UPDATE_ALL);
+
+        if (sl.getBlockEntity(anchorPos) instanceof VideoAnchorBlockEntity be) {
+            // Surface normal of the wall we're painting on points outward in the same direction
+            // as the face the player clicked.
+            be.setFacing(face);
+            ServerPlayNetworking.send(sp, new OpenScreenPayload(anchorPos, be.toNbt()));
+        }
+        return InteractionResult.SUCCESS;
     }
 }

src/main/java/com/ejclaw/videoplayer/net/DeleteAnchorPayload.java

@@ -0,0 +1,24 @@
+package com.ejclaw.videoplayer.net;
+
+import com.ejclaw.videoplayer.VideoPlayerMod;
+import net.minecraft.core.BlockPos;
+import net.minecraft.network.RegistryFriendlyByteBuf;
+import net.minecraft.network.codec.StreamCodec;
+import net.minecraft.network.protocol.common.custom.CustomPacketPayload;
+import net.minecraft.resources.Identifier;
+
+/** C2S — delete an anchor from the VideoConfigScreen. */
+public record DeleteAnchorPayload(BlockPos pos) implements CustomPacketPayload {
+    public static final CustomPacketPayload.Type<DeleteAnchorPayload> TYPE =
+        new CustomPacketPayload.Type<>(Identifier.fromNamespaceAndPath(VideoPlayerMod.MOD_ID, "delete_anchor"));
+
+    public static final StreamCodec<RegistryFriendlyByteBuf, DeleteAnchorPayload> CODEC = StreamCodec.composite(
+        BlockPos.STREAM_CODEC, DeleteAnchorPayload::pos,
+        DeleteAnchorPayload::new
+    );
+
+    @Override
+    public Type<? extends CustomPacketPayload> type() {
+        return TYPE;
+    }
+}

src/main/java/com/ejclaw/videoplayer/net/OpenScreenPayload.java

@@ -0,0 +1,27 @@
+package com.ejclaw.videoplayer.net;
+
+import com.ejclaw.videoplayer.VideoPlayerMod;
+import net.minecraft.core.BlockPos;
+import net.minecraft.nbt.CompoundTag;
+import net.minecraft.network.RegistryFriendlyByteBuf;
+import net.minecraft.network.codec.ByteBufCodecs;
+import net.minecraft.network.codec.StreamCodec;
+import net.minecraft.network.protocol.common.custom.CustomPacketPayload;
+import net.minecraft.resources.Identifier;
+
+/** S2C — open the VideoConfigScreen for an anchor on the client. */
+public record OpenScreenPayload(BlockPos pos, CompoundTag data) implements CustomPacketPayload {
+    public static final CustomPacketPayload.Type<OpenScreenPayload> TYPE =
+        new CustomPacketPayload.Type<>(Identifier.fromNamespaceAndPath(VideoPlayerMod.MOD_ID, "open_screen"));
+
+    public static final StreamCodec<RegistryFriendlyByteBuf, OpenScreenPayload> CODEC = StreamCodec.composite(
+        BlockPos.STREAM_CODEC, OpenScreenPayload::pos,
+        ByteBufCodecs.COMPOUND_TAG, OpenScreenPayload::data,
+        OpenScreenPayload::new
+    );
+
+    @Override
+    public Type<? extends CustomPacketPayload> type() {
+        return TYPE;
+    }
+}

src/main/java/com/ejclaw/videoplayer/net/SaveConfigPayload.java

@@ -0,0 +1,27 @@
+package com.ejclaw.videoplayer.net;
+
+import com.ejclaw.videoplayer.VideoPlayerMod;
+import net.minecraft.core.BlockPos;
+import net.minecraft.nbt.CompoundTag;
+import net.minecraft.network.RegistryFriendlyByteBuf;
+import net.minecraft.network.codec.ByteBufCodecs;
+import net.minecraft.network.codec.StreamCodec;
+import net.minecraft.network.protocol.common.custom.CustomPacketPayload;
+import net.minecraft.resources.Identifier;
+
+/** C2S — save edited config from VideoConfigScreen back to the server. */
+public record SaveConfigPayload(BlockPos pos, CompoundTag data) implements CustomPacketPayload {
+    public static final CustomPacketPayload.Type<SaveConfigPayload> TYPE =
+        new CustomPacketPayload.Type<>(Identifier.fromNamespaceAndPath(VideoPlayerMod.MOD_ID, "save_config"));
+
+    public static final StreamCodec<RegistryFriendlyByteBuf, SaveConfigPayload> CODEC = StreamCodec.composite(
+        BlockPos.STREAM_CODEC, SaveConfigPayload::pos,
+        ByteBufCodecs.COMPOUND_TAG, SaveConfigPayload::data,
+        SaveConfigPayload::new
+    );
+
+    @Override
+    public Type<? extends CustomPacketPayload> type() {
+        return TYPE;
+    }
+}

src/main/java/com/ejclaw/videoplayer/net/SyncAnchorPayload.java

@@ -0,0 +1,27 @@
+package com.ejclaw.videoplayer.net;
+
+import com.ejclaw.videoplayer.VideoPlayerMod;
+import net.minecraft.core.BlockPos;
+import net.minecraft.nbt.CompoundTag;
+import net.minecraft.network.RegistryFriendlyByteBuf;
+import net.minecraft.network.codec.ByteBufCodecs;
+import net.minecraft.network.codec.StreamCodec;
+import net.minecraft.network.protocol.common.custom.CustomPacketPayload;
+import net.minecraft.resources.Identifier;
+
+/** S2C — push current anchor state to clients tracking the chunk. */
+public record SyncAnchorPayload(BlockPos pos, CompoundTag data) implements CustomPacketPayload {
+    public static final CustomPacketPayload.Type<SyncAnchorPayload> TYPE =
+        new CustomPacketPayload.Type<>(Identifier.fromNamespaceAndPath(VideoPlayerMod.MOD_ID, "sync_anchor"));
+
+    public static final StreamCodec<RegistryFriendlyByteBuf, SyncAnchorPayload> CODEC = StreamCodec.composite(
+        BlockPos.STREAM_CODEC, SyncAnchorPayload::pos,
+        ByteBufCodecs.COMPOUND_TAG, SyncAnchorPayload::data,
+        SyncAnchorPayload::new
+    );
+
+    @Override
+    public Type<? extends CustomPacketPayload> type() {
+        return TYPE;
+    }
+}

src/main/java/com/ejclaw/videoplayer/net/VideoPlayerNetwork.java

@@ -0,0 +1,109 @@
+package com.ejclaw.videoplayer.net;
+
+import com.ejclaw.videoplayer.VideoPlayerMod;
+import com.ejclaw.videoplayer.block.VideoAnchorBlockEntity;
+import net.fabricmc.fabric.api.networking.v1.PayloadTypeRegistry;
+import net.fabricmc.fabric.api.networking.v1.PlayerLookup;
+import net.fabricmc.fabric.api.networking.v1.ServerPlayNetworking;
+import net.minecraft.core.BlockPos;
+import net.minecraft.nbt.CompoundTag;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.server.permissions.Permissions;
+import net.minecraft.world.level.block.Block;
+import net.minecraft.world.level.block.Blocks;
+
+/**
+ * Registers all four payload types and the two C2S server-side receivers.
+ * Client-side receivers are registered in {@code com.ejclaw.videoplayer.client.net.ClientNetworking}.
+ */
+public final class VideoPlayerNetwork {
+    private VideoPlayerNetwork() {}
+
+    public static void registerPayloadTypes() {
+        // S2C
+        PayloadTypeRegistry.clientboundPlay().register(OpenScreenPayload.TYPE, OpenScreenPayload.CODEC);
+        PayloadTypeRegistry.clientboundPlay().register(SyncAnchorPayload.TYPE, SyncAnchorPayload.CODEC);
+        // C2S
+        PayloadTypeRegistry.serverboundPlay().register(SaveConfigPayload.TYPE, SaveConfigPayload.CODEC);
+        PayloadTypeRegistry.serverboundPlay().register(DeleteAnchorPayload.TYPE, DeleteAnchorPayload.CODEC);
+    }
+
+    public static void registerServerReceivers() {
+        ServerPlayNetworking.registerGlobalReceiver(SaveConfigPayload.TYPE, (payload, context) -> {
+            ServerPlayer player = context.player();
+            ServerLevel level = player.level();
+            BlockPos pos = payload.pos();
+            CompoundTag data = payload.data();
+            context.server().execute(() -> handleSave(level, player, pos, data));
+        });
+
+        ServerPlayNetworking.registerGlobalReceiver(DeleteAnchorPayload.TYPE, (payload, context) -> {
+            ServerPlayer player = context.player();
+            ServerLevel level = player.level();
+            BlockPos pos = payload.pos();
+            context.server().execute(() -> handleDelete(level, player, pos));
+        });
+    }
+
+    private static void handleSave(ServerLevel level, ServerPlayer player, BlockPos pos, CompoundTag data) {
+        if (!canModify(player, pos)) {
+            VideoPlayerMod.LOG.warn("[{}] {} attempted save without permission at {}",
+                VideoPlayerMod.MOD_ID, player.getName().getString(), pos);
+            return;
+        }
+        if (!(level.getBlockEntity(pos) instanceof VideoAnchorBlockEntity be)) {
+            return;
+        }
+        be.applyFromNbt(sanitize(data));
+        // broadcast updated state to all players tracking the chunk
+        SyncAnchorPayload sync = new SyncAnchorPayload(pos, be.toNbt());
+        for (ServerPlayer watcher : PlayerLookup.tracking(level, pos)) {
+            ServerPlayNetworking.send(watcher, sync);
+        }
+    }
+
+    private static void handleDelete(ServerLevel level, ServerPlayer player, BlockPos pos) {
+        if (!canModify(player, pos)) {
+            return;
+        }
+        if (level.getBlockEntity(pos) instanceof VideoAnchorBlockEntity) {
+            level.setBlock(pos, Blocks.AIR.defaultBlockState(), Block.UPDATE_ALL);
+        }
+    }
+
+    /** Permission check: creative players or operators may modify anchors. */
+    public static boolean canModify(ServerPlayer player, BlockPos pos) {
+        if (player.isCreative()) return true;
+        return player.permissions().hasPermission(Permissions.COMMANDS_GAMEMASTER);
+    }
+
+    /** Strip out unexpected keys from C2S NBT before applying. */
+    private static CompoundTag sanitize(CompoundTag in) {
+        CompoundTag out = new CompoundTag();
+        out.putString("url", trimUrl(in.getStringOr("url", "")));
+        out.putInt("width", clamp(in.getIntOr("width", 1), 1, 32));
+        out.putInt("height", clamp(in.getIntOr("height", 1), 1, 32));
+        out.putString("facing", in.getStringOr("facing", "north"));
+        out.putBoolean("loop", in.getBooleanOr("loop", true));
+        out.putFloat("volume", Math.max(0F, Math.min(1F, in.getFloatOr("volume", 0.5F))));
+        out.putBoolean("muted", in.getBooleanOr("muted", false));
+        out.putBoolean("autoplay", in.getBooleanOr("autoplay", true));
+        return out;
+    }
+
+    private static String trimUrl(String s) {
+        if (s == null) return "";
+        String t = s.trim();
+        if (t.length() > 256) t = t.substring(0, 256);
+        // SPEC §4.4: only https?:// or empty
+        if (!t.isEmpty() && !(t.startsWith("http://") || t.startsWith("https://"))) {
+            return "";
+        }
+        return t;
+    }
+
+    private static int clamp(int v, int lo, int hi) {
+        return Math.max(lo, Math.min(hi, v));
+    }
+}

src/main/java/com/ejclaw/videoplayer/registry/VideoPlayerBlockEntities.java

@@ -3,17 +3,17 @@ package com.ejclaw.videoplayer.registry;
 import com.ejclaw.videoplayer.VideoPlayerMod;
 import com.ejclaw.videoplayer.block.VideoAnchorBlockEntity;
 import net.fabricmc.fabric.api.object.builder.v1.block.entity.FabricBlockEntityTypeBuilder;
-import net.minecraft.block.entity.BlockEntityType;
+import net.minecraft.core.registries.BuiltInRegistries;
-import net.minecraft.registry.Registries;
+import net.minecraft.core.Registry;
-import net.minecraft.registry.Registry;
+import net.minecraft.resources.Identifier;
-import net.minecraft.util.Identifier;
+import net.minecraft.world.level.block.entity.BlockEntityType;
 
 public final class VideoPlayerBlockEntities {
     private VideoPlayerBlockEntities() {}
 
     public static final BlockEntityType<VideoAnchorBlockEntity> VIDEO_ANCHOR = Registry.register(
-        Registries.BLOCK_ENTITY_TYPE,
+        BuiltInRegistries.BLOCK_ENTITY_TYPE,
-        Identifier.of(VideoPlayerMod.MOD_ID, "video_anchor"),
+        Identifier.fromNamespaceAndPath(VideoPlayerMod.MOD_ID, "video_anchor"),
         FabricBlockEntityTypeBuilder.create(VideoAnchorBlockEntity::new, VideoPlayerBlocks.VIDEO_ANCHOR).build()
     );
 

src/main/java/com/ejclaw/videoplayer/registry/VideoPlayerBlocks.java

@@ -2,20 +2,24 @@ package com.ejclaw.videoplayer.registry;
 
 import com.ejclaw.videoplayer.VideoPlayerMod;
 import com.ejclaw.videoplayer.block.VideoAnchorBlock;
-import net.minecraft.block.AbstractBlock;
+import net.minecraft.core.registries.BuiltInRegistries;
-import net.minecraft.block.Block;
+import net.minecraft.core.Registry;
-import net.minecraft.registry.Registries;
+import net.minecraft.resources.Identifier;
-import net.minecraft.registry.Registry;
+import net.minecraft.resources.ResourceKey;
-import net.minecraft.registry.RegistryKey;
+import net.minecraft.world.level.block.Block;
-import net.minecraft.registry.RegistryKeys;
+import net.minecraft.world.level.block.state.BlockBehaviour;
-import net.minecraft.util.Identifier;
 
 public final class VideoPlayerBlocks {
     private VideoPlayerBlocks() {}
 
     public static final Block VIDEO_ANCHOR = register(
         "video_anchor",
-        AbstractBlock.Settings.create().strength(1.0F).nonOpaque(),
+        BlockBehaviour.Properties.of()
+            .noCollision()
+            .noOcclusion()
+            .instabreak()
+            .replaceable()
+            .strength(0F),
         VideoAnchorBlock::new
     );
 
@@ -25,13 +29,13 @@ public final class VideoPlayerBlocks {
 
     @FunctionalInterface
     private interface BlockFactory<B extends Block> {
-        B create(AbstractBlock.Settings settings);
+        B create(BlockBehaviour.Properties properties);
     }
 
-    private static <B extends Block> B register(String name, AbstractBlock.Settings settings, BlockFactory<B> factory) {
+    private static <B extends Block> B register(String name, BlockBehaviour.Properties props, BlockFactory<B> factory) {
-        Identifier id = Identifier.of(VideoPlayerMod.MOD_ID, name);
+        Identifier id = Identifier.fromNamespaceAndPath(VideoPlayerMod.MOD_ID, name);
-        RegistryKey<Block> key = RegistryKey.of(RegistryKeys.BLOCK, id);
+        ResourceKey<Block> key = ResourceKey.create(BuiltInRegistries.BLOCK.key(), id);
-        B block = factory.create(settings.registryKey(key));
+        B block = factory.create(props.setId(key));
-        return Registry.register(Registries.BLOCK, key, block);
+        return Registry.register(BuiltInRegistries.BLOCK, key, block);
     }
 }

src/main/java/com/ejclaw/videoplayer/registry/VideoPlayerItems.java

@@ -2,34 +2,33 @@ package com.ejclaw.videoplayer.registry;
 
 import com.ejclaw.videoplayer.VideoPlayerMod;
 import com.ejclaw.videoplayer.item.VideoStickItem;
-import net.minecraft.item.Item;
+import net.minecraft.core.registries.BuiltInRegistries;
-import net.minecraft.registry.Registries;
+import net.minecraft.core.Registry;
-import net.minecraft.registry.Registry;
+import net.minecraft.resources.Identifier;
-import net.minecraft.registry.RegistryKey;
+import net.minecraft.resources.ResourceKey;
-import net.minecraft.registry.RegistryKeys;
+import net.minecraft.world.item.Item;
-import net.minecraft.util.Identifier;
 
 public final class VideoPlayerItems {
     private VideoPlayerItems() {}
 
     public static final Item VIDEO_STICK = register(
         "video_stick",
-        settings -> new VideoStickItem(settings.maxCount(1))
+        props -> new VideoStickItem(props.stacksTo(1))
     );
 
     public static void register() {
-        // For M1 we don't add to a vanilla item group; players get the stick via /videoStick.
+        // players get the stick via /videoStick command
     }
 
     @FunctionalInterface
     private interface ItemFactory<I extends Item> {
-        I create(Item.Settings settings);
+        I create(Item.Properties properties);
     }
 
     private static <I extends Item> I register(String name, ItemFactory<I> factory) {
-        Identifier id = Identifier.of(VideoPlayerMod.MOD_ID, name);
+        Identifier id = Identifier.fromNamespaceAndPath(VideoPlayerMod.MOD_ID, name);
-        RegistryKey<Item> key = RegistryKey.of(RegistryKeys.ITEM, id);
+        ResourceKey<Item> key = ResourceKey.create(BuiltInRegistries.ITEM.key(), id);
-        I item = factory.create(new Item.Settings().registryKey(key));
+        I item = factory.create(new Item.Properties().setId(key));
-        return Registry.register(Registries.ITEM, key, item);
+        return Registry.register(BuiltInRegistries.ITEM, key, item);
     }
 }

src/main/resources/assets/video_player/blockstates/video_anchor.json

@@ -0,0 +1,5 @@
+{
+  "variants": {
+    "": { "model": "video_player:block/video_anchor" }
+  }
+}

src/main/resources/assets/video_player/items/video_stick.json

@@ -0,0 +1,6 @@
+{
+  "model": {
+    "type": "minecraft:model",
+    "model": "video_player:item/video_stick"
+  }
+}

src/main/resources/assets/video_player/models/block/video_anchor.json

@@ -0,0 +1,5 @@
+{
+  "textures": {
+    "particle": "video_player:block/video_anchor"
+  }
+}

src/main/resources/assets/video_player/models/item/video_stick.json

@@ -0,0 +1,6 @@
+{
+  "parent": "item/generated",
+  "textures": {
+    "layer0": "video_player:item/video_stick"
+  }
+}

src/main/resources/fabric.mod.json

@@ -16,9 +16,9 @@
     "client": [ "com.ejclaw.videoplayer.VideoPlayerClient" ]
   },
   "depends": {
-    "fabricloader": ">=0.16.0",
+    "fabricloader": ">=0.19.0",
     "fabric-api": "*",
-    "minecraft": ">=1.21.6",
+    "minecraft": "${target_minecraft}",
-    "java": ">=21"
+    "java": ">=25"
   }
 }