MediaCodec audio/video muxing issues ond Android

问题:

I am transcoding videos based on the example given by Google (https://android.googlesource.com/platform/cts/+/master/tests/tests/media/src/android/media/cts/ExtractDecodeEditEncodeMuxTest.java)

Basically, transocding of MP4 files works, but on some phones I get some weird results. If for example I transcode a video with audio on an HTC One, the code won't give any errors but the file cannot play afterward on the phone. If I have a 10 seconds video it jumps to almost the last second and you only here some crackling noise. If you play the video with VLC the audio track is completely muted.

I did not alter the code in terms of encoding/decoding and the same code gives correct results on a Nexus 5 or MotoX for example.

Anybody having an idea why it might fail on that specific device?

Best regard and thank you, Florian

回答1:

I made it work in Android 4.4.2 devices by following changes:

• Set AAC profile to AACObjectLC instead of AACObjectHE

private static final int OUTPUT_AUDIO_AAC_PROFILE = MediaCodecInfo.CodecProfileLevel.AACObjectLC;

• During creation of output audio format, use sample rate and channel count of input format instead of fixed values

MediaFormat outputAudioFormat = MediaFormat.createAudioFormat(OUTPUT_AUDIO_MIME_TYPE,
inputFormat.getInteger(MediaFormat.KEY_SAMPLE_RATE),
inputFormat.getInteger(MediaFormat.KEY_CHANNEL_COUNT));

• Put a check just before audio muxing audio track to control presentation timestamps. (To avoid timestampUs X < lastTimestampUs X for Audio track error)

    if (audioPresentationTimeUsLast == 0) { // Defined in the begining of method
      audioPresentationTimeUsLast = audioEncoderOutputBufferInfo.presentationTimeUs;
    } else {
      if (audioPresentationTimeUsLast > audioEncoderOutputBufferInfo.presentationTimeUs) {
        audioEncoderOutputBufferInfo.presentationTimeUs = audioPresentationTimeUsLast + 1;
      }
      audioPresentationTimeUsLast = audioEncoderOutputBufferInfo.presentationTimeUs;
    }

    // Write data

    if (audioEncoderOutputBufferInfo.size != 0) {
       muxer.writeSampleData(outputAudioTrack, encoderOutputBuffer, audioEncoderOutputBufferInfo);
    }

Hope this helps...

回答2:

If original CTS tests fail you need to go to device vendors and ask for fixes