FFMPEG Plugin: Refactor out chunk loading in audio path.

- Main reasons are to increase readability of audio path and to demonstrate
  that chunk loading in audio and video path is the same code that can be
  focused in one method (instead of two at the moment). Added a TODO for
  collapsing both methods into one and the conditions that must hold true to
  do so (just in case I'll be hitted by a bus and someone else has to proceed).
  Collapsing is scheduled for a later commit.

- Added documentation for the new method accordingly.

- Make use of full line length in comments of
  _LoadNextVideoChunkIfNeededAndAssignStartTime().

- No functional change intended.

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

@@ -728,36 +728,10 @@ AVCodecDecoder::_DecodeNextAudioFrame()
 			continue;
 		}
 
-		if (fTempPacket.size == 0) {
-			// Time to read the next chunk buffer. We use a separate
-			// media_header, since the chunk header may not belong to
-			// the start of the decoded audio frames we return. For
-			// example we may have used frames from a previous invokation,
-			// or we may have to read several chunks until we fill up the
-			// output buffer.
-			media_header chunkMediaHeader;
-			status_t err = GetNextChunk(&fChunkBuffer, &fChunkBufferSize,
-				&chunkMediaHeader);
-			if (err == B_LAST_BUFFER_ERROR) {
-				TRACE_AUDIO("  Last Chunk with chunk size %ld\n",
-					fChunkBufferSize);
-				fChunkBufferSize = 0;
-				return err;
-			}
-			if (err != B_OK || fChunkBufferSize < 0) {
-				printf("GetNextChunk error %ld\n",fChunkBufferSize);
-				fChunkBufferSize = 0;
-				break;
-			}
-			fTempPacket.data
-				= static_cast<uint8_t*>(const_cast<void*>(fChunkBuffer));
-			fTempPacket.size = fChunkBufferSize;
-			fTempPacket.dts = chunkMediaHeader.start_time;
-				// Let FFMPEG handle the correct relationship between
-				// start_time and decoded audio frames. By doing so we are
-				// merely following the way it is done for the video path
-				// see _LoadNextVideoChunkIfNeededAndAssignStartTime()
-		}
+		status_t loadingChunkStatus
+			= _LoadNextAudioChunkIfNeededAndAssignStartTime();
+		if (loadingChunkStatus != B_OK)
+			return loadingChunkStatus;
 
 		status_t decodingStatus
 			= _DecodeSomeAudioFramesIntoEmptyDecodedDataBuffer();
@@ -794,6 +768,69 @@ AVCodecDecoder::_DecodeNextAudioFrame()
 }
 
 
+/*! \brief Loads the next audio chunk into fChunkBuffer and assigns it
+		(including the start time) to fTempPacket accordingly only if
+		fTempPacket is empty.
+
+	\returns B_OK
+		1. meaning: Next audio chunk is loaded.
+		2. meaning: No need to load and assign anything. Proceed as usual.
+	\returns B_LAST_BUFFER_ERROR No more audio chunks available.
+		fChunkBuffer and fTempPacket are left untouched.
+	\returns Other errors Caller should bail out because fChunkBuffer and
+		fTempPacket are in unknown states. Normal operation cannot be
+		guaranteed.
+*/
+status_t
+AVCodecDecoder::_LoadNextAudioChunkIfNeededAndAssignStartTime()
+{
+	// TODO: Collapse _LoadNextAudioChunkIfNeededAndAssignStartTime() and
+	// _LoadNextVideoChunkIfNeededAndAssignStartTime() into one method called
+	// _LoadNextChunkIfNeededAndAssignStartTime() once the following conditions
+	// are met:
+	//     1. There is no longer a distinction between fVideoChunkBuffer and
+	//        fChunkBuffer.
+	//     2. _LoadNextAudioChunkIfNeededAndAssignStartTime() adds Padding to
+	//        the chunk buffer, too, like it is done in
+	//        _LoadNextVideoChunkIfNeededAndAssignStartTime() at the moment.
+
+	if (fTempPacket.size > 0)
+		return B_OK;
+
+	const void* chunkBuffer = NULL;
+	size_t chunkBufferSize = 0;
+		// In the case that GetNextChunk() returns an error fChunkBufferSize
+		// should be left untouched.
+	media_header chunkMediaHeader;
+
+	status_t getNextChunkStatus = GetNextChunk(&chunkBuffer, &chunkBufferSize,
+		&chunkMediaHeader);
+	if (getNextChunkStatus != B_OK)
+		return getNextChunkStatus;
+
+	fChunkBuffer = chunkBuffer;
+	fChunkBufferSize = chunkBufferSize;
+
+	fTempPacket.data
+		= static_cast<uint8_t*>(const_cast<void*>(fChunkBuffer));
+	fTempPacket.size = fChunkBufferSize;
+	fTempPacket.dts = chunkMediaHeader.start_time;
+		// Let FFMPEG handle the correct relationship between start_time and
+		// decoded audio frames. By doing so we are merely following the way it
+		// is done for the video path.
+		// see _LoadNextVideoChunkIfNeededAndAssignStartTime()
+		//
+		// FIXME: Research how to establish a meaningful relationship
+		// between start_time and decoded audio frame when the received chunk
+		// buffer contains partial video frames. Maybe some data formats
+		// contain time stamps (ake pts / dts fields) that can be evaluated by
+		// FFMPEG. But as long as I don't have such audio data to test it, it
+		// makes no sense to implement it.
+
+	return B_OK;
+}
+
+
 /*!	\brief Tries to decode at least one audio frame and store it in the
 		fDecodedDataBuffer.
 
@@ -1053,8 +1090,8 @@ AVCodecDecoder::_LoadNextVideoChunkIfNeededAndAssignStartTime()
 		// should be left untouched.
 	media_header chunkMediaHeader;
 
-	status_t getNextChunkStatus = GetNextChunk(&chunkBuffer,
-		&chunkBufferSize, &chunkMediaHeader);
+	status_t getNextChunkStatus = GetNextChunk(&chunkBuffer, &chunkBufferSize,
+		&chunkMediaHeader);
 	if (getNextChunkStatus != B_OK)
 		return getNextChunkStatus;
 
@@ -1073,18 +1110,17 @@ AVCodecDecoder::_LoadNextVideoChunkIfNeededAndAssignStartTime()
 		// \see http://git.videolan.org/?p=ffmpeg.git;a=blob;f=ffplay.c;h=09623db374e5289ed20b7cc28c262c4375a8b2e4;hb=9153b33a742c4e2a85ff6230aea0e75f5a8b26c2#l1502
 		//
 		// FIXME: Research how to establish a meaningful relationship
-		// between start_time and decoded video frame when the received
-		// chunk buffer contains partial video frames. Maybe some data
-		// formats contain time stamps (ake pts / dts fields) that can
-		// be evaluated by FFMPEG. But as long as I don't have such
-		// video data to test it, it makes no sense to implement it.
+		// between start_time and decoded video frame when the received chunk
+		// buffer contains partial video frames. Maybe some data formats
+		// contain time stamps (ake pts / dts fields) that can be evaluated by
+		// FFMPEG. But as long as I don't have such video data to test it, it
+		// makes no sense to implement it.
 		//
-		// FIXME: Implement tracking start_time of video frames
-		// originating in data chunks that encode more than one video
-		// frame at a time. In that case on would increment the
-		// start_time for each consecutive frame of such a data chunk
-		// (like it is done for audio frame decoding). But as long as
-		// I don't have such video data to test it, it makes no sense
+		// FIXME: Implement tracking start_time of video frames originating in
+		// data chunks that encode more than one video frame at a time. In that
+		// case on would increment the start_time for each consecutive frame of
+		// such a data chunk (like it is done for audio frame decoding). But as
+		// long as I don't have such video data to test it, it makes no sense
 		// to implement it.
 
 #ifdef LOG_STREAM_TO_FILE

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

@@ -61,6 +61,7 @@ private:
 							media_header* mediaHeader,
 							media_decode_info* info);
 			status_t	_DecodeNextAudioFrame();
+			status_t	_LoadNextAudioChunkIfNeededAndAssignStartTime();
 			status_t	_DecodeSomeAudioFramesIntoEmptyDecodedDataBuffer();
 			status_t	_DecodeNextVideoFrame();
 			void		_ApplyEssentialVideoContainerPropertiesToContext();