我正在尝试将基本的原始 AAC 数据写入文件，希望可以使用 mp4parser 将其与视频轨道一起封装。为此，我需要将任何给定的音频文件编码为该格式。MediaCodec API 从 API 16 开始就很容易获得，所以我决定将它用于编解码器操作。
我不确定为什么网上没有多少资源可用，这可能是由于相关的复杂性。虽然，我已经设法了解到基本方法应该是：
通过 MediaExtractor -> Enqueue decoder input buffer -> Dequeue output buffer 获取样本数据并获取解码后的数据 -> Enqueue encoder input buffer -> Dequeue encoder output buffer -> 将编码后的数据写入文件。
private void transcodeFile(File source, File destination) throws IOException {
FileInputStream inputStream = new FileInputStream(source);
FileOutputStream outputStream = new FileOutputStream(destination);
log("Transcoding file: " + source.getName());
MediaExtractor extractor;
MediaCodec encoder;
MediaCodec decoder;
ByteBuffer[] encoderInputBuffers;
ByteBuffer[] encoderOutputBuffers;
ByteBuffer[] decoderInputBuffers;
ByteBuffer[] decoderOutputBuffers;
int noOutputCounter = 0;
int noOutputCounterLimit = 10;
extractor = new MediaExtractor();
extractor.setDataSource(inputStream.getFD());
extractor.selectTrack(0);
log(String.format("TRACKS #: %d", extractor.getTrackCount()));
MediaFormat format = extractor.getTrackFormat(0);
String mime = format.getString(MediaFormat.KEY_MIME);
log(String.format("MIME TYPE: %s", mime));
final String outputType = MediaFormat.MIMETYPE_AUDIO_AAC;
encoder = MediaCodec.createEncoderByType(outputType);
MediaFormat encFormat = MediaFormat.createAudioFormat(outputType, 44100, 2);
encFormat.setInteger(MediaFormat.KEY_BIT_RATE, 64000);
encoder.configure(encFormat, null, null, MediaCodec.CONFIGURE_FLAG_ENCODE);
decoder = MediaCodec.createDecoderByType(mime);
decoder.configure(format, null, null, 0);
encoder.start();
decoder.start();
encoderInputBuffers = encoder.getInputBuffers();
encoderOutputBuffers = encoder.getOutputBuffers();
decoderInputBuffers = decoder.getInputBuffers();
decoderOutputBuffers = decoder.getOutputBuffers();
int timeOutUs = 1000;
long presentationTimeUs = 0;
MediaCodec.BufferInfo info = new MediaCodec.BufferInfo();
boolean inputEOS = false;
boolean outputEOS = false;
while(!outputEOS && noOutputCounter < noOutputCounterLimit) {
noOutputCounter++;
if(!inputEOS) {
int decInputBufferIndex = decoder.dequeueInputBuffer(timeOutUs);
log("decInputBufferIndex: " + decInputBufferIndex);
if (decInputBufferIndex >= 0) {
ByteBuffer dstBuffer = decoderInputBuffers[decInputBufferIndex];
//Getting sample with MediaExtractor
int sampleSize = extractor.readSampleData(dstBuffer, 0);
if (sampleSize < 0) {
inputEOS = true;
log("Input EOS");
sampleSize = 0;
} else {
presentationTimeUs = extractor.getSampleTime();
}
log("Input sample size: " + sampleSize);
//Enqueue decoder input buffer
decoder.queueInputBuffer(decInputBufferIndex, 0, sampleSize, presentationTimeUs, inputEOS ? MediaCodec.BUFFER_FLAG_END_OF_STREAM : 0);
if (!inputEOS) extractor.advance();
} else {
log("decInputBufferIndex: " + decInputBufferIndex);
}
}
//Dequeue decoder output buffer
int res = decoder.dequeueOutputBuffer(info, timeOutUs);
if(res >= 0) {
if(info.size > 0) noOutputCounter = 0;
int decOutputBufferIndex = res;
log("decOutputBufferIndex: " + decOutputBufferIndex);
ByteBuffer buffer = decoderOutputBuffers[decOutputBufferIndex];
buffer.position(info.offset);
buffer.limit(info.offset + info.size);
final int size = buffer.limit();
if(size > 0) {
//audioTrack.write(buffer, buffer.limit(), AudioTrack.MODE_STATIC);
int encInputBufferIndex = encoder.dequeueInputBuffer(-1);
log("encInputBufferIndex: " + encInputBufferIndex);
//fill the input buffer with the decoded data
if(encInputBufferIndex >= 0) {
ByteBuffer dstBuffer = encoderInputBuffers[encInputBufferIndex];
dstBuffer.clear();
dstBuffer.put(buffer);
encoder.queueInputBuffer(encInputBufferIndex, 0, info.size, info.presentationTimeUs, 0);
int encOutputBufferIndex = encoder.dequeueOutputBuffer(info, timeOutUs);
if(encOutputBufferIndex >= 0) {
log("encOutputBufferIndex: " + encOutputBufferIndex);
ByteBuffer outBuffer = encoderOutputBuffers[encOutputBufferIndex];
byte[] out = new byte[outBuffer.remaining()];
outBuffer.get(out);
//write data to file
outputStream.write(out);
}
}
}
decoder.releaseOutputBuffer(decOutputBufferIndex, false);
if((info.flags & MediaCodec.BUFFER_FLAG_END_OF_STREAM) != 0) {
outputEOS = true;
log("Output EOS");
}
} else if (res == MediaCodec.INFO_OUTPUT_BUFFERS_CHANGED) {
decoderOutputBuffers = decoder.getOutputBuffers();
log("Output buffers changed.");
} else if (res == MediaCodec.INFO_OUTPUT_FORMAT_CHANGED) {
log("Output format changed.");
} else {
log("Dequeued output buffer returned: " + res);
}
}
log("Stopping..");
releaseCodec(decoder);
releaseCodec(encoder);
inputStream.close();
outputStream.close();
}
由于某种原因，输出文件无效。为什么？
编辑：设法修复异常，问题仍然存在。
编辑 2：我通过在编码器格式设置中将缓冲区大小设置为比特率来防止缓冲区溢出。目前有两个问题： 1.在很短的时间间隔之后，它就卡在这里了，可能会无限期地等待。int encInputBufferIndex = dequeueInputBuffer(-1);
2.解码只要track就是，为什么要考虑实际的采样间隔？
编辑 3：使用 AudioTrack.write() 进行测试，音频播放得很好，但这不是故意的，并且表明解码正在与正在馈送的媒体文件同步进行，这应该尽可能快地进行以允许编码器快速完成工作。更改decoder.queueInputBuffer() 中的presentationTimeUs 什么也没做。