I use the MediaCodec class provided by the Android SDK since API level 16 with the OMX.SEC.aac.enc encoder to encode audio to a file. I get the audio
input from the AudioRecord class. My instance of the AudioRecord class is configured like this:
bufferSize = AudioRecord.getMinBufferSize(44100, AudioFormat.CHANNEL_IN_STEREO, AudioFormat.ENCODING_PCM_16BIT);
recorder = new AudioRecord(MediaRecorder.AudioSource.MIC, 44100, AudioFormat.CHANNEL_IN_STEREO, AudioFormat.ENCODING_DEFAULT, bufferSize);
I am able to play the raw data from the AudioRecord instance, so the problem does not reside there.
I write the output from the AudioRecord instance to a ByteBuffer instance and pass it to an available input buffer from the encoder. The output from the encoder is written to a file on the SD-card.
These are the configuration parameters for my MediaCodec instance:
codec = MediaCodec.createEncoderByType("audio/mp4a-latm");
MediaFormat format = new MediaFormat();
format.setString(MediaFormat.KEY_MIME, "audio/mp4a-latm");
format.setInteger(MediaFormat.KEY_BIT_RATE, 64 * 1024);
format.setInteger(MediaFormat.KEY_CHANNEL_COUNT, 2);
format.setInteger(MediaFormat.KEY_SAMPLE_RATE, 44100);
format.setInteger(MediaFormat.KEY_AAC_PROFILE, MediaCodecInfo.CodecProfileLevel.AACObjectHE);
codec.configure(format, null, null, MediaCodec.CONFIGURE_FLAG_ENCODE);
VLC tells me that there are no streams in my aac file. The command FFMPEG -i @filename@ gives me the following error: Invalid data found when processing input. None of the mediaplayers I tested are able to play my file.
Why am I unable to play my file? I receive no OpenMAX errors in LogCat and the application does not crash when encoding. I wrote a video encoder that works on the same principle and it works.
This is the code to read the data from the AudioRecord instance to a buffer:
new Thread() {
public void run() {
ByteBuffer byteBuffer = ByteBuffer.allocateDirect(bufferSize);
int read = 0;
while (isRecording) {
read = recorder.read(byteBuffer, bufferSize);
if(AudioRecord.ERROR_INVALID_OPERATION != read){
encoder.add(byteBuffer);
}
}
recorder.stop();
}
}.start();
The function add from my encoder copies the content of one buffer to another:
public void add(ByteBuffer input) {
if (!isRunning)
return;
if (tmpInputBuffer == null)
tmpInputBuffer = ByteBuffer.allocate(input.capacity());
if (!tmpBufferClear)
Log.e("audio encoder", "deadline missed"); //TODO lower bit rate
synchronized (tmpInputBuffer) {
tmpInputBuffer.clear();
tmpInputBuffer.put(input);
tmpInputBuffer.notifyAll();
Log.d("audio encoder", "pushed data into tmpInputBuffer");
}
}
The following code is used to occupy the input buffer of the encoder:
new Thread() {
public void run() {
while (isRunning) {
if (tmpInputBuffer == null)
continue;
synchronized (tmpInputBuffer) {
if (tmpBufferClear) {
try {
Log.d("audio encoder", "falling asleep");
tmpInputBuffer.wait(); //wait when no input is available
}
catch (InterruptedException e) {
e.printStackTrace();
}
}
ByteBuffer[] inputBuffers = codec.getInputBuffers();
int inputBufferIndex;
do
inputBufferIndex = codec.dequeueInputBuffer(-1);
while (inputBufferIndex < 0);
ByteBuffer inputBuffer = inputBuffers[inputBufferIndex];
inputBuffer.clear();
Log.d("input buffer size", String.valueOf(inputBuffer.capacity()));
Log.d("tmp input buffer size", String.valueOf(tmpInputBuffer.capacity()));
inputBuffer.put(tmpInputBuffer.array());
tmpInputBuffer.clear();
codec.queueInputBuffer(inputBufferIndex, 0, tmpInputBuffer.capacity(), 0, 0);
tmpBufferClear = true;
Log.d("audio encoder", "added to input buffer");
}
}
}
}.start();
I write the output from the encoder to a local file like this:
new Thread() {
public void run() {
while (isRunning) {
ByteBuffer[] outputBuffers = codec.getOutputBuffers();
MediaCodec.BufferInfo bufferInfo = new MediaCodec.BufferInfo();
int outputBufferIndex = codec.dequeueOutputBuffer(bufferInfo, -1);
while (outputBufferIndex >= 0) {
ByteBuffer outputBuffer = outputBuffers[outputBufferIndex];
byte[] outData = new byte[bufferInfo.size];
outputBuffer.get(outData);
try {
fileWriter.write(outData, 0, outData.length);
}
catch (IOException e) {
e.printStackTrace();
}
codec.releaseOutputBuffer(outputBufferIndex, false);
outputBufferIndex = codec.dequeueOutputBuffer(bufferInfo, 0);
Log.d("audio encoder", "removed from output buffer");
}
}
codec.stop();
try {
fileWriter.close();
}
catch (IOException e) {
e.printStackTrace();
}
}
}.start();
tmpBufferClear = true;
Log.d("audio encoder", "added to input buffer");
}
}
}
}.start();