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I'm trying to play some audio taken from an MPEG2 transport (.ts) file. I'm getting the audio stream via MediaExtractor, using readSampleData to copy samples to MediaCodec input buffers, then writing the MediaCodec output buffer to an AudioTrack. MediaExtractor indicates the audio MIME type as "audio/mp4a-latm".

All this works wonderfully on a Nexus 7 2013 tablet.

But it does not work at all on an inexpensive Neutab x7 tablet. The problem is that after a few samples, dequeueInputBuffer repeatedly returns -1. Commenting out the call to AudioTrack.write() does not change that fact, so the issue is with the operation of MediaCodec.

The code looks like (logging, some error handling omitted):

  audioInputBufferIndex = audioCodec.dequeueInputBuffer(TIMEOUT);
  if (audioInputBufferIndex >= 0) {
    audioInputBuffers[audioInputBufferIndex].clear();
    sampleSize = audioExtractor.readSampleData(audioInputBuffers[audioInputBufferIndex], 0);
    audioPresentationTimeUs = audioExtractor.getSampleTime();
    audioCodec.queueInputBuffer(audioInputBufferIndex,0,sampleSize,audioPresentationTimeUs,0);
    audioOutputBufferIndex = audioCodec.dequeueOutputBuffer(audioBufferInfo, TIMEOUT);
    if (audioOutputBufferIndex >= 0) {
      ByteBuffer buffer = audioOutputBuffers[audioOutputBufferIndex];
      byte[] chunk = new byte[audioBufferInfo.size];
      buffer.get(chunk);
      buffer.clear();
      if (audioTrack != null & chunk.length > 0) {
        audioTrack.write(chunk, 0, chunk.length);
        audioExtractor.advance();
      }
      audioCodec.releaseOutputBuffer(audioOutputBufferIndex,false);

The audioCodec is configured with a MediaFormat obtained from audioExtractor. I've tried increasing the TIMEOUT to large values, no joy.

Why would this code behave differently on these two devices? Any knobs to turn?

There is a "Videos" app on the Neutab that plays this file just fine.Logcat reveals that it's also using MediaExtractor and AudioTrack but not, appparently, MediaCodec. I see Omx* entries in logcat, so maybe it's using libstagefright directly.

Paul Steckler
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  • If you're not sure whether the device works with simple MediaCodec usage, grab a copy of Grafika and confirm that all of the activities work (https://github.com/google/grafika). More examples are on http://bigflake.com/mediacodec/ . – fadden Mar 06 '15 at 17:15

1 Answers1

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As far as I read your code, you only try to dequeue output buffers once every time you manage to queue one input buffer.

Keep in mind that the decoder runs asynchronously, and has got a limited number of input and output buffers. Even if the decoder does decode your input buffer, the output may not be available in an output buffer immediately. Increasing the TIMEOUT value in this case could maybe help, but it's not guaranteed.

Try splitting your two if statements, so that you call dequeueOutputBuffer every time around in the loop, even if dequeueInputBuffer didn't return any buffer.

mstorsjo
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  • Yes, that helped. And advance should be called every time you get an input buffer. With those changes, the code works fine. – Paul Steckler Mar 06 '15 at 19:15