daemon/src/chardev_client.c

@@ -181,6 +181,29 @@ static int handle_req_decode(struct chardev_client *cli,
 		 req.capture_width, req.capture_height,
 		 req.capture_num_planes);
 
+	/*
+	 * Degenerate-bitstream filter (issue #17): libva-v4l2-request-
+	 * fourier flushes a stub packet into the OUTPUT_MPLANE queue at
+	 * playback-pause boundaries.  The payload is shorter than any
+	 * parseable H.264 NAL (3-byte start code + 1-byte NAL header =
+	 * 4 bytes minimum); avcodec_send_packet returns
+	 * AVERROR_INVALIDDATA, which we used to propagate to the kernel
+	 * as a decode failure.  Firefox then marks H.264-via-VAAPI as
+	 * broken for the session and routes every subsequent frame to
+	 * libmozavcodec SW — pause never recovers to HW.
+	 *
+	 * Drop the request as a no-op decode and reply RESP_FRAME OK so
+	 * libva's V4L2 state machine keeps its surface pool alive.
+	 */
+	if (req.bitstream_len < 4) {
+		log_info("REQ_DECODE cookie=%u: tiny bitstream %u bytes — dropping as no-op (pause-time sentinel)",
+			 hdr->cookie, req.bitstream_len);
+		memset(&resp, 0, sizeof(resp));
+		resp.status = DAEDALUS_DECODE_NO_FRAME;
+		return send_response(cli, DAEDALUS_MSG_RESP_FRAME,
+				     hdr->cookie, &resp, sizeof(resp));
+	}
+
 	/*
 	 * Open dmabuf-fds for every CAPTURE plane and mmap them.
 	 * If this fails we still attempt the decode (so the kernel