使用MediaCodec解码原始AAC而不使用MediaExtractor

Question

我使用MediaExtractor和MediaCodec成功解码并播放mp4（AAC）文件，代码如下。我想将原始AAC（在另一个文件中，使用相同的编码格式）解码到PCM。问题是我不知道如何在没有mediaExtractor的情况下设置 SampleSize 和 presentationTimeUs 。如何在不使用MediaExtractor的情况下设置上述参数？

//使用此格式从PCM创建的songwav.mp4文件

MediaFormat outputFormat = MediaFormat.createAudioFormat(
            "audio/mp4a-latm", 44100, 2);
    outputFormat.setInteger(MediaFormat.KEY_AAC_PROFILE,
            MediaCodecInfo.CodecProfileLevel.AACObjectLC);
    outputFormat.setInteger(MediaFormat.KEY_BIT_RATE,
            128000);

//解码

String inputfilePath = Environment.getExternalStorageDirectory()
            .getPath() + "/" + "songwav.mp4";
String outputFilePath = Environment.getExternalStorageDirectory()
            .getPath() + "/" + "songwavmp4.pcm";
OutputStream outputStream = new FileOutputStream(outputFilePath);
    MediaCodec codec;
    AudioTrack audioTrack;

// extractor gets information about the stream
MediaExtractor extractor = new MediaExtractor();
extractor.setDataSource(inputfilePath);

        MediaFormat format = extractor.getTrackFormat(0);
    String mime = format.getString(MediaFormat.KEY_MIME);

    // the actual decoder
    codec = MediaCodec.createDecoderByType(mime);
    codec.configure(format, null /* surface */, null /* crypto */, 0 /* flags */);
    codec.start();
    ByteBuffer[] codecInputBuffers = codec.getInputBuffers();
    ByteBuffer[] codecOutputBuffers = codec.getOutputBuffers();

    // get the sample rate to configure AudioTrack
    int sampleRate = format.getInteger(MediaFormat.KEY_SAMPLE_RATE);

    // create our AudioTrack instance
    audioTrack = new AudioTrack(AudioManager.STREAM_MUSIC, sampleRate,
            AudioFormat.CHANNEL_OUT_STEREO, AudioFormat.ENCODING_PCM_16BIT,
            AudioTrack.getMinBufferSize(sampleRate,
                    AudioFormat.CHANNEL_OUT_STEREO,
                    AudioFormat.ENCODING_PCM_16BIT), AudioTrack.MODE_STREAM);

    // start playing, we will feed you later
    audioTrack.play();
    extractor.selectTrack(0);

    // start decoding
    final long kTimeOutUs = 10000;
    MediaCodec.BufferInfo BufInfo = new MediaCodec.BufferInfo();
    boolean sawInputEOS = false;
    boolean sawOutputEOS = false;

    int inputBufIndex;

    int counter=0;
while (!sawOutputEOS) {


        counter++;
        if (!sawInputEOS) {
            inputBufIndex = codec.dequeueInputBuffer(kTimeOutUs);
            // Log.d(LOG_TAG, " bufIndexCheck " + bufIndexCheck);
            if (inputBufIndex >= 0) {
                ByteBuffer dstBuf = codecInputBuffers[inputBufIndex];

                int sampleSize = extractor
                        .readSampleData(dstBuf, 0 /* offset */);

                long presentationTimeUs = 0;

                if (sampleSize < 0) {

                    sawInputEOS = true;
                    sampleSize = 0;
                } else {

                    presentationTimeUs = extractor.getSampleTime();
                }
                // can throw illegal state exception (???)

                codec.queueInputBuffer(inputBufIndex, 0 /* offset */,
                        sampleSize, presentationTimeUs,
                        sawInputEOS ? MediaCodec.BUFFER_FLAG_END_OF_STREAM
                                : 0);

                if (!sawInputEOS) {
                    extractor.advance();
                }
            } else {
                Log.e("sohail", "inputBufIndex " + inputBufIndex);
            }
        }

        int res = codec.dequeueOutputBuffer(BufInfo, kTimeOutUs);

        if (res >= 0) {
            Log.i("sohail","decoding: deqOutputBuffer >=0, counter="+counter);
            // Log.d(LOG_TAG, "got frame, size " + info.size + "/" +
            // info.presentationTimeUs);
            if (BufInfo.size > 0) {
                // noOutputCounter = 0;
            }

            int outputBufIndex = res;
            ByteBuffer buf = codecOutputBuffers[outputBufIndex];

            final byte[] chunk = new byte[BufInfo.size];
            buf.get(chunk);
            buf.clear();

            if (chunk.length > 0) {
                // play
                audioTrack.write(chunk, 0, chunk.length);
                // write to file
                outputStream.write(chunk);

            }
            codec.releaseOutputBuffer(outputBufIndex, false /* render */);
            if ((BufInfo.flags & MediaCodec.BUFFER_FLAG_END_OF_STREAM) != 0) {
                Log.i("sohail", "saw output EOS.");
                sawOutputEOS = true;
            }
        } else if (res == MediaCodec.INFO_OUTPUT_BUFFERS_CHANGED) {
            codecOutputBuffers = codec.getOutputBuffers();

            Log.i("sohail", "output buffers have changed.");
        } else if (res == MediaCodec.INFO_OUTPUT_FORMAT_CHANGED) {
            MediaFormat oformat = codec.getOutputFormat();

            Log.i("sohail", "output format has changed to " + oformat);
        } else {
            Log.i("sohail", "dequeueOutputBuffer returned " + res);
        }
    }

    Log.d(LOG_TAG, "stopping...");

    // ////////closing
    if (audioTrack != null) {
        audioTrack.flush();
        audioTrack.release();
        audioTrack = null;
    }

    outputStream.flush();
    outputStream.close();

    codec.stop();