MediaCodec AAC -> PCM Decoder Configuration on Android

I'm trying to implement AAC -> PCM Decoder by MediaCodec.

Firstly, I successfully implemented PCM -> AAC Encoder by MediaCodec as intended as below

private boolean setEncoder(int rate) { encoder = MediaCodec.createEncoderByType("audio/mp4a-latm"); MediaFormat format = new MediaFormat(); format.setString(MediaFormat.KEY_MIME, "audio/mp4a-latm"); format.setInteger(MediaFormat.KEY_CHANNEL_COUNT, 1); format.setInteger(MediaFormat.KEY_SAMPLE_RATE, 44100); format.setInteger(MediaFormat.KEY_BIT_RATE, 64 * 1024);//AAC-HE 64kbps format.setInteger(MediaFormat.KEY_AAC_PROFILE, MediaCodecInfo.CodecProfileLevel.AACObjectHE); encoder.configure(format, null, null, MediaCodec.CONFIGURE_FLAG_ENCODE); return true; } 

INPUT: PCM Bitrate = 44100(Hz) x 16(bit) x 1(Monoral) = 705600 bit/s

OUTPUT: AAC-HE Bitrate = 64 x 1024(bit) = 65536 bit/s

So, the data size is approximately compressed x11 ,and I confirmed this working by observing a log

• AudioRecoder﹕ 4096 bytes read
• AudioEncoder﹕ 369 bytes encoded

the data size is approximately compressed x11, so far so good.

Now, I have a UDP server to receive the encoded data, then decode it.

The decoder profile is set as follows:

private boolean setDecoder(int rate) { decoder = MediaCodec.createDecoderByType("audio/mp4a-latm"); MediaFormat format = new MediaFormat(); format.setString(MediaFormat.KEY_MIME, "audio/mp4a-latm"); format.setInteger(MediaFormat.KEY_CHANNEL_COUNT, 1); format.setInteger(MediaFormat.KEY_SAMPLE_RATE, 44100); format.setInteger(MediaFormat.KEY_BIT_RATE, 64 * 1024);//AAC-HE 64kbps format.setInteger(MediaFormat.KEY_AAC_PROFILE, MediaCodecInfo.CodecProfileLevel.AACObjectHE); decoder.configure(format, null, null, 0); return true; } 

Since UDPserver packet buffer size is 1024

• UDPserver ﹕ 1024 bytes received

and since this is the compressed AAC data, I would expect the decoding size will be

approximately 1024 x11, however the actual result is

• AudioDecoder﹕ 8192 bytes decoded

It's approximately x8, and I feel something wrong.

Can anyone give me a thought on this issue? Thank you.

PS.

The decoder code is as follows just in case:

byte[] buffer2 = new byte[1024]; DatagramPacket packet = new DatagramPacket(buffer2, buffer2.length); //.............. //receive UDP packet here.............. ds.receive(packet); sockAddress = packet.getSocketAddress(); address = sockAddress.toString(); // now decoding inputBuffers = decoder.getInputBuffers(); outputBuffers = decoder.getOutputBuffers(); inputBufferIndex = decoder.dequeueInputBuffer(-1); if (inputBufferIndex >= 0) { inputBuffer = inputBuffers[inputBufferIndex]; inputBuffer.clear(); inputBuffer.put(buffer2); decoder.queueInputBuffer(inputBufferIndex, 0, buffer2.length, 0, 0); } bufferInfo = new MediaCodec.BufferInfo(); outputBufferIndex = decoder.dequeueOutputBuffer(bufferInfo, 0); while (outputBufferIndex >= 0) { outputBuffer = outputBuffers[outputBufferIndex]; outData = new byte[bufferInfo.size]; outputBuffer.get(outData); Log.d("AudioDecoder", outData.length + " bytes decoded"); decoder.releaseOutputBuffer(outputBufferIndex, false); outputBufferIndex = decoder.dequeueOutputBuffer(bufferInfo, 0); }