FFMPEG-Plugin: Implement decoding of streamed video data.

- This commit makes the mpeg2_decoder_test successfully decode the test video
  into 84 consecutive PNG images, yeah :)

- If this commit broke playing video files for you please file a bug report.
  I've tested only with one video file (big_buck_bunny_720p_stereo.ogg) that
  everything still works.

- The implementation has some shortcomings though, that will be addressed with
  some later commits:
    1. Start time of media header is wrongly calculated. At the moment we are
       using the start time of the first encoded data chunk we read via
       GetNextChunk(). This works only for chunk that contain one and exactly
       one frame, but not for chunks that contain the end or middle of a frame.
    2. Fields of the media header aren't updated when there is a format change
       in the middle of the video stream (for example the pixel aspect ratio
       might change in the middle of a DVB video stream (e.g. switch from 4:3
       to 16:9)).

- Also fix a potential bug, where the CODEC_FLAG_TRUNCATED flag was always
  set, due to missing brackets.

Signed-off-by: Colin Günther <[email protected]>

src/add-ons/media/plugins/ffmpeg/AVCodecDecoder.cpp

@@ -15,6 +15,7 @@
 
 #include <new>
 
+#include <assert.h>
 #include <string.h>
 
 #include <Bitmap.h>
@@ -251,8 +252,12 @@ AVCodecDecoder::SeekedTo(int64 frame, bigtime_t time)
 {
 	status_t ret = B_OK;
 	// Reset the FFmpeg codec to flush buffers, so we keep the sync
-	if (fCodecInitDone)
+	if (fCodecInitDone) {
 		avcodec_flush_buffers(fContext);
+		av_init_packet(&fTempPacket);
+		fTempPacket.size = 0;
+		fTempPacket.data = NULL;
+	}
 
 	// Flush internal buffers as well.
 	fChunkBuffer = NULL;
@@ -430,10 +435,11 @@ AVCodecDecoder::_NegotiateVideoOutputFormat(media_format* inOutFormat)
 	fContext->extradata = (uint8_t*)fExtraData;
 	fContext->extradata_size = fExtraDataSize;
 
-	if (fCodec->capabilities & CODEC_CAP_TRUNCATED)
+	if (fCodec->capabilities & CODEC_CAP_TRUNCATED) {
 		// Expect and handle video frames to be splitted across consecutive
 		// data chunks.
 		fContext->flags |= CODEC_FLAG_TRUNCATED;
+	}
 
 	TRACE("  requested video format 0x%x\n",
 		inOutFormat->u.raw_video.display.format);
@@ -516,6 +522,10 @@ AVCodecDecoder::_NegotiateVideoOutputFormat(media_format* inOutFormat)
 	inOutFormat->require_flags = 0;
 	inOutFormat->deny_flags = B_MEDIA_MAUI_UNDEFINED_FLAGS;
 
+	av_init_packet(&fTempPacket);
+	fTempPacket.size = 0;
+	fTempPacket.data = NULL;
+
 #ifdef TRACE_AV_CODEC
 	char buffer[1024];
 	string_for_format(*inOutFormat, buffer, sizeof(buffer));
@@ -700,24 +710,35 @@ AVCodecDecoder::_DecodeVideo(void* outBuffer, int64* outFrameCount,
 status_t
 AVCodecDecoder::_DecodeNextVideoFrame()
 {
+	assert(fTempPacket.size >= 0);
+
 	bool firstRun = true;
 	while (true) {
 		media_header chunkMediaHeader;
-		status_t err = GetNextChunk(&fChunkBuffer, &fChunkBufferSize,
-			&chunkMediaHeader);
-		if (err != B_OK) {
-			TRACE("AVCodecDecoder::_DecodeVideo(): error from "
-				"GetNextChunk(): %s\n", strerror(err));
-			return err;
-		}
+
+		if (fTempPacket.size == 0) {
+			// Our packet buffer is empty, so fill it now.
+			status_t getNextChunkStatus	= GetNextChunk(&fChunkBuffer,
+				&fChunkBufferSize, &chunkMediaHeader);
+			if (getNextChunkStatus != B_OK) {
+				TRACE("AVCodecDecoder::_DecodeNextVideoFrame(): error from "
+					"GetNextChunk(): %s\n", strerror(err));
+				return getNextChunkStatus;
+			}
+
+			fTempPacket.data = static_cast<uint8_t*>(const_cast<void*>(
+				fChunkBuffer));
+			fTempPacket.size = fChunkBufferSize;
+
 #ifdef LOG_STREAM_TO_FILE
-		if (sDumpedPackets < 100) {
-			sStreamLogFile.Write(fChunkBuffer, fChunkBufferSize);
-			printf("wrote %ld bytes\n", fChunkBufferSize);
-			sDumpedPackets++;
-		} else if (sDumpedPackets == 100)
-			sStreamLogFile.Unset();
+			if (sDumpedPackets < 100) {
+				sStreamLogFile.Write(fChunkBuffer, fChunkBufferSize);
+				printf("wrote %ld bytes\n", fChunkBufferSize);
+				sDumpedPackets++;
+			} else if (sDumpedPackets == 100)
+				sStreamLogFile.Unset();
 #endif
+		}
 
 		if (firstRun) {
 			firstRun = false;
@@ -746,24 +767,28 @@ AVCodecDecoder::_DecodeNextVideoFrame()
 		bigtime_t startTime = system_time();
 #endif
 
-		// NOTE: In the FFmpeg code example I've read, the length returned by
-		// avcodec_decode_video() is completely ignored. Furthermore, the
-		// packet buffers are supposed to contain complete frames only so we
-		// don't seem to be required to buffer any packets because not the
-		// complete packet has been read.
-		fTempPacket.data = (uint8_t*)fChunkBuffer;
-		fTempPacket.size = fChunkBufferSize;
+		// NOTE: In the FFMPEG 0.10.2 code example decoding_encoding.c, the
+		// length returned by avcodec_decode_video2() is used to update the
+		// packet buffer size (here it is fTempPacket.size). This way the
+		// packet buffer is allowed to contain incomplete frames so we are
+		// required to buffer the packets between different calls to
+		// _DecodeNextVideoFrame().
 		int gotPicture = 0;
-		int len = avcodec_decode_video2(fContext, fRawDecodedPicture,
-			&gotPicture, &fTempPacket);
-		if (len < 0) {
-			TRACE("[v] AVCodecDecoder: error in decoding frame %lld: %d\n",
-				fFrame, len);
-			// NOTE: An error from avcodec_decode_video() seems to be ignored
-			// in the ffplay sample code.
-//			return B_ERROR;
+		int decodedDataSizeInBytes = avcodec_decode_video2(fContext,
+			fRawDecodedPicture, &gotPicture, &fTempPacket);
+		if (decodedDataSizeInBytes < 0) {
+			TRACE("[v] AVCodecDecoder: ignoring error in decoding frame %lld:"
+				" %d\n", fFrame, len);
+			// NOTE: An error from avcodec_decode_video2() is ignored by the
+			// FFMPEG 0.10.2 example decoding_encoding.c. Only the packet
+			// buffers are flushed accordingly
+			fTempPacket.data = NULL;
+			fTempPacket.size = 0;
+			continue;
 		}
 
+		fTempPacket.size -= decodedDataSizeInBytes;
+		fTempPacket.data += decodedDataSizeInBytes;
 
 //TRACE("FFDEC: PTS = %d:%d:%d.%d - fContext->frame_number = %ld "
 //	"fContext->frame_rate = %ld\n", (int)(fContext->pts / (60*60*1000000)),