Android - 使用 mediacodec 编码 aac 音频时出现 BufferOverflowException

Question

I am trying to encode some audio streams with aac codec using Mediacodec . For this I'm using this implementation google cts ExtractDecodeEncodeMusTest .

For some aac files it throws BufferOverflowException after encoding some frames. To be more precise, it throws exception at line no 1030, encoderInputBuffer.put(decoderOutputBuffer); .

I am configuring the outputAudioFormat as following:

MediaFormat outputAudioFormat = MediaFormat.createAudioFormat(
        inputAudioFormat.getString(MediaFormat.KEY_MIME),
        inputAudioFormat.getInteger(MediaFormat.KEY_SAMPLE_RATE),
        inputAudioFormat.getInteger(MediaFormat.KEY_CHANNEL_COUNT)            
);
outputAudioFormat.setInteger(MediaFormat.KEY_BIT_RATE, outputAudioBitRate);

I'm completely clueless about how to resolve this. Any kind of help would be really appreciated.

Stacktrace with some log:

W/MPEG4Writer: Timed-out waiting for video track to reach final audio timestamp !
D/MPEG4Writer: Video track source stopping
    Video track source stopped
    Video track stopped. Stop source
    Duration from tracks range is [0, 125135] us
    Stopping writer thread
D/MPEG4Writer: 0 chunks are written in the last batch
D/MPEG4Writer: Writer thread stopped
W/System.err: java.nio.BufferOverflowException
        at java.nio.ByteBuffer.put(ByteBuffer.java:611)
        at java.nio.DirectByteBuffer.put(DirectByteBuffer.java:256)

• Device: Xiaomi POCO x3
• OS: Android 10

Sample file's info that causing the overflow:

Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/storage/emulated/0/Sample/sample.mp4':
      Metadata:
        major_brand     : isom
        minor_version   : 512
        compatible_brands: isomiso2avc1mp41
        creation_time   : 2017-11-10T09:36:00.000000Z
        encoder         : Lavf57.71.100
      Duration: 01:58:17.26, start: 0.000000, bitrate: 2726 kb/s
        Stream #0:0(und): Video: h264, 1 reference frame (avc1 / 0x31637661), yuv420p(left), 1920x804 (1920x816) [SAR 1:1 DAR 160:67], 2497 kb/s, 23.98 fps, 23.98 tbr, 11988 tbn, 47.95 tbc (default)
        Metadata:
          creation_time   : 2017-11-10T09:36:00.000000Z
          handler_name    : VideoHandler
        Stream #0:1(eng): Audio: aac (mp4a / 0x6134706D), 48000 Hz, 5.1, fltp, 224 kb/s (default)
        Metadata:
          creation_time   : 2017-11-10T09:36:00.000000Z
          handler_name    : SoundHandler

Update:

Log says audioDecoderOutputBufferInfo.size= 12288 || encoderInputBuffer.limit()= 4096 audioDecoderOutputBufferInfo.size= 12288 || encoderInputBuffer.limit()= 4096 before throwing the overflow exception.

And log of decoderOutputAudioFormat :

audio decoder: output format changed: {sample-rate=48000, pcm-encoding=2, mime=audio/raw, channel-count=6}

Answer 1

BufferOverflowException happens when there is no agreement between the producer (eg decoder) and the consumer (eg encoder) about the size of the buffers.

When you configure the encoder, it allocates input buffers based on the information in the MediaFormat that it receives. The standard packet size for AAC is 1024 frames. Frame size = sample size * channel count. PCM 16-bit (default encoding) uses 2 bytes per sample.

So, based on the information you gave it, the encoder is supposed to allocate buffers of size 1024 * 2 * 6 = 12288 bytes. However, in your case it actually allocates only 4096 bytes. So I assume that the encoder ignored the channel-count property and defaulted to 2 channels. Possibly, it printed some warning to the log.

One thing that you can still do is to manually reduce the number of channels in every frame to at most 2. You will need to allocate a new buffer and copy the decoded data into it while skipping every Nth sample. And don't forget to rewind the resulting buffer before you pass it to the encoder.