playback issues

sam-tool-tauri/src-tauri/src/decoder.rs

@@ -309,6 +309,20 @@ impl Drop for DecoderSession {
     }
 }
 
+/// Pack a frame for the JS wire: 8-byte little-endian i64 frame index
+/// followed by the raw JPEG. The backend is authoritative on which frame
+/// actually decoded — JS reads the prefix to bind paints to the real frame
+/// number rather than the optimistic request, which matters when codec
+/// keyframe-snap or seek-ahead returns something other than the requested
+/// index. (Today our ffmpeg path is exact-seek so they always match, but
+/// the prefix makes the system robust to that ever changing.)
+pub fn pack_frame(idx: u64, jpeg: &[u8]) -> Vec<u8> {
+    let mut out = Vec::with_capacity(8 + jpeg.len());
+    out.extend_from_slice(&(idx as i64).to_le_bytes());
+    out.extend_from_slice(jpeg);
+    out
+}
+
 /// Pick a VAAPI render node. `SAM_TOOL_VAAPI_DEVICE` overrides; otherwise we
 /// probe `/dev/dri/renderD128..199` for the first that exists. Multi-GPU
 /// systems can end up with the integrated card on D128 and a discrete card