Fix black-screen video on unaligned widths (swscale row padding)

swscale aligns the RGBA linesize to a SIMD boundary, so any video whose
width*4 isn't a multiple of the alignment (e.g. 1674-wide → 6720 B/row vs
6696) yields a padded plane larger than width*height*4. The old copy path
tripped a `need > expected → skip` guard and dropped every video frame,
leaving a black screen while audio (independent path) still played.

Read Frame.imageStride and strip the row padding with a row-by-row memCopy
into a tightly-packed slot (width*height*4), matching the texture's expected
size. Falls back to deriving the stride from buffer size when the field is
absent. Single-shot memCopy retained when stride == rowBytes (aligned widths).

Co-Authored-By: Claude Opus 4 <noreply@anthropic.com>

gradle.properties

@@ -5,7 +5,7 @@ org.gradle.configuration-cache=false
 
 # Mod
 mod_id=video_player
-mod_version=0.4.32
+mod_version=0.4.33
 maven_group=com.ejclaw.videoplayer
 archives_base_name=video_player
 

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

@@ -276,6 +276,14 @@ public class JavaCvBackend implements VideoBackend {
             Class<?> frameCls    = Class.forName(FRAME_CLASS);
             Field imageField     = frameCls.getField("image");
             Field samplesField   = frameCls.getField("samples");
+            // Row stride (bytes) of frame.image[0]. swscale aligns the RGBA linesize to a SIMD
+            // boundary (32/64 B), so for any width whose width*4 isn't already aligned the plane
+            // is padded: e.g. 1674-wide → linesize 6720 instead of 6696. We read this to strip
+            // the padding row-by-row; resolved defensively so a Frame without the field just
+            // falls back to deriving the stride from the buffer size below.
+            Field strideField;
+            try { strideField = frameCls.getField("imageStride"); }
+            catch (Throwable t) { strideField = null; }
             // Java2DFrameConverter is no longer used now that we read RGBA bytes directly,
             // but we still resolve its class so a future code path could fall back to it if a
             // grabber refuses setPixelFormat. Keep the lookup defensive.
@@ -323,26 +331,40 @@ public class JavaCvBackend implements VideoBackend {
                     // primary memory-churn problem; 0.4.10 fixed that; 0.4.11 adds the ring on
                     // top to absorb the burst-then-stall caused by SourceDataLine backpressure
                     // pacing only at audio-buffer granularity.
-                    int need = src.remaining();
-                    // Reviewer-mandated sanity bounds: memCopy is a raw native copy with no
-                    // fence against overrun. Validate against (a) the source buffer's own
-                    // capacity (so a corrupt plane can't read past it) and (b) the expected
-                    // RGBA frame size (width*height*4) (so an unexpectedly oversized plane
-                    // can't smash the dst slot we'll allocate). If either fails, skip this
-                    // frame and continue — the next grab() will give us a fresh one.
-                    int expected = width * height * 4;
-                    if (need > src.capacity()) {
-                        VideoPlayerMod.LOG.warn("[{}] frame overruns source capacity (need={}, cap={}); skipping",
-                            VideoPlayerMod.MOD_ID, need, src.capacity());
-                        need = 0;
-                    } else if (need > expected) {
-                        VideoPlayerMod.LOG.warn("[{}] frame larger than expected RGBA size (need={}, expected={}); skipping",
-                            VideoPlayerMod.MOD_ID, need, expected);
-                        need = 0;
+                    // The destination texture is tightly packed: one frame = width*height*4
+                    // bytes with no row padding (consumeFrame copies ringBytes[idx] straight
+                    // into a w*h*4 GPU texture and rejects anything larger). swscale, however,
+                    // hands us an RGBA plane whose linesize is SIMD-aligned, so for any width
+                    // where width*4 isn't a multiple of the alignment the source rows carry
+                    // trailing padding (e.g. 1674-wide → 6720 B/row vs the 6696 B we want).
+                    // Copying the padded buffer verbatim both overruns the tight dst slot and
+                    // shears the image; we must strip the pad row-by-row.
+                    int rowBytes = width * 4;            // bytes of real pixels per row
+                    int dstBytes = rowBytes * height;    // tightly-packed frame size
+                    // Source row stride: prefer Frame.imageStride (authoritative), else derive
+                    // it from the buffer size. Guard against a stride smaller than a full row
+                    // (bogus field) by falling back to the tight rowBytes.
+                    int strideBytes = rowBytes;
+                    if (strideField != null) {
+                        try {
+                            int s = strideField.getInt(frame);
+                            if (s >= rowBytes) strideBytes = s;
+                        } catch (Throwable ignored) {}
+                    } else if (height > 0) {
+                        int s = src.remaining() / height;
+                        if (s >= rowBytes) strideBytes = s;
                     }
-                    if (need > 0) {
+                    // Sanity bound: the strided read must stay within the source buffer. memCopy
+                    // is a raw native copy with no overrun fence, so if the plane is smaller than
+                    // stride*height (corrupt/truncated) skip this frame and grab a fresh one.
+                    boolean ok = dstBytes > 0 && (long) strideBytes * height <= src.capacity();
+                    if (!ok && dstBytes > 0) {
+                        VideoPlayerMod.LOG.warn("[{}] frame plane too small (stride={}, h={}, cap={}); skipping",
+                            VideoPlayerMod.MOD_ID, strideBytes, height, src.capacity());
+                    }
+                    if (ok) {
                         int srcPos = src.position();
-                        long srcAddr = MemoryUtil.memAddress(src) + srcPos;
+                        long srcBase = MemoryUtil.memAddress(src) + srcPos;
                         synchronized (frameLock) {
                             // Recheck shutdown inside the lock: stopWorker() flipped running=false
                             // before signaling, so worker is the only writer here and grabber.close()
@@ -350,12 +372,21 @@ public class JavaCvBackend implements VideoBackend {
                             // the contract obvious to future readers.
                             if (!running.get() || closed) break;
                             int idx = ringTail;
-                            if (ringBufs[idx] == null || ringBufs[idx].capacity() < need) {
-                                ringBufs[idx] = ByteBuffer.allocateDirect(need).order(ByteOrder.nativeOrder());
+                            if (ringBufs[idx] == null || ringBufs[idx].capacity() < dstBytes) {
+                                ringBufs[idx] = ByteBuffer.allocateDirect(dstBytes).order(ByteOrder.nativeOrder());
                             }
-                            long dstAddr = MemoryUtil.memAddress(ringBufs[idx]);
-                            MemoryUtil.memCopy(srcAddr, dstAddr, need);
-                            ringBytes[idx] = need;
+                            long dstBase = MemoryUtil.memAddress(ringBufs[idx]);
+                            if (strideBytes == rowBytes) {
+                                MemoryUtil.memCopy(srcBase, dstBase, dstBytes);
+                            } else {
+                                // Strip swscale row padding: copy only the real pixels per row.
+                                for (int y = 0; y < height; y++) {
+                                    MemoryUtil.memCopy(srcBase + (long) y * strideBytes,
+                                                       dstBase + (long) y * rowBytes,
+                                                       rowBytes);
+                                }
+                            }
+                            ringBytes[idx] = dstBytes;
                             ringTail = (idx + 1) % FRAME_RING_SLOTS;
                             if (ringCount < FRAME_RING_SLOTS) {
                                 ringCount++;