MediaCodec之Decoder
1.介绍：
MediaCodec类可用于访问Android底层的媒体编解码器，也就是，编码器/解码器组件。它是Android底层多媒体支持基本架构的一部分（通常与MediaExtractor, MediaSync, MediaMuxer, MediaCrypto, MediaDrm, Image, Surface, 以及AudioTrack一起使用）；MediaCodec作为比较年轻的Android多媒体硬件编解码框架，在终端硬解方案中带来了很大便利。Android源码中的CTS部分也给出了很多可以关于Media编解码的Demo。
2.解码
Android的MediaCodec解码需要分为视频、音频解码。
首先获取MediaCodec支持的数量，根据MediaCodec的句柄获取MediaCodec支持的编解码格式
MediaCodecList.getCodecCount()
MediaCodecList.getCodecInfoAt(i);
比如通过以下测试代码，就可以知道终端MediaCodec的解码能力：
int n = MediaCodecList.getCodecCount();
for (int i = 0; i < n; ++i) {
MediaCodecInfo info = MediaCodecList.getCodecInfoAt(i);
String[] supportedTypes = info.getSupportedTypes();
boolean mime_support = false;
if(info.isEncoder()){
return;
}
for (int j = 0; j < supportedTypes.length; ++j) {
Log.d(TAG, "codec info:" + info.getName()+" supportedTypes:" + supportedTypes[j]);
if (supportedTypes[j].equalsIgnoreCase(mime)) {
mime_support = true;
}
}
}
code
surpport
OMX.amlogic.hevc.decoder.awesome
video/hevc
OMX.amlogic.avc.decoder.awesome
video/avc
OMX.amlogic.mpeg4.decoder.awesome
video/mp4v-es
OMX.amlogic.h263.decoder.awesome
video/3gpp
OMX.amlogic.mpeg2.decoder.awesome
video/mpeg2
OMX.amlogic.vc1.decoder.awesome
video/vc1
OMX.amlogic.vc1.decoder.awesome
video/wvc1
OMX.amlogic.wmv3.decoder.awesome
video/wmv3
OMX.amlogic.mjpeg.decoder.awesome
video/mjpeg
OMX.google.amrnb.decoder
audio/3gpp
OMX.google.amrwb.decoder
audio/amr-wb
OMX.google.aac.decoder
audio/mp4a-latm
OMX.google.adif.decoder
audio/aac-adif
OMX.google.latm.decoder
audio/aac-latm
OMX.google.adts.decoder
audio/adts
OMX.google.g711.alaw.decoder
audio/g711-alaw
OMX.google.g711.mlaw.decoder
audio/g711-mlaw
OMX.google.adpcm.ima.decoder
audio/adpcm-ima
OMX.google.adpcm.ms.decoder
audio/adpcm-ms
OMX.google.vorbis.decoder
audio/vorbis
OMX.google.alac.decoder
audio/alac
OMX.google.wma.decoder
audio/wma
OMX.google.wmapro.decoder
audio/wmapro
OMX.google.ape.decoder
audio/ape
OMX.google.truehd.decoder
audio/truehd
OMX.google.ffmpeg.decoder
audio/ffmpeg
OMX.google.raw.decoder
audio/raw
OMX.google.mpeg4.decoder
video/mp4v-es
OMX.google.h263.decoder
video/3gpp
OMX.google.h264.decoder
video/avc
OMX.google.vp8.decoder
video/x-vnd.on2.vp8
OMX.google.vp9.decoder
video/x-vnd.on2.vp9
OMX.google.vp6.decoder
video/x-vnd.on2.vp6
OMX.google.vp6a.decoder
video/x-vnd.on2.vp6a
OMX.google.vp6f.decoder
video/x-vnd.on2.vp6f
OMX.google.rm10.decoder
video/rm10
OMX.google.rm20.decoder
video/rm20
OMX.google.rm40.decoder
video/rm40
OMX.google.wmv2.decoder
video/wmv2
OMX.google.wmv1.decoder
video/wmv1
AML.google.ac3.decoder
audio/ac3
AML.google.ec3.decoder
audio/eac3
OMX.google.mp2.decoder
audio/mpeg-L2
OMX.google.mp3.decoder
audio/mpeg
AML.google.dtshd.decoder
audio/dtshd
OMX.google.raw.decoder
audio/raw
OMX.google.vp6.decoder
video/x-vnd.on2.vp6
OMX.google.vp6a.decoder
video/x-vnd.on2.vp6a
OMX.google.vp6f.decoder
video/x-vnd.on2.vp6f
OMX.google.h265.decoder
video/hevc
OMX.google.wmv2.decoder
video/wmv2
OMX.google.wmv2.decoder
video/wmv1
Android提供了MediaExtractor来分离本地/网络视频流的音视频。
首先定义了一个统一音视频处理的类：
public class MediaDecoder extends Thread{
protected String mVideoFilePath = null;
public static final long TIME_US = 10000;
protected MediaExtractor mExtractor = null;
protected MediaCodec mDecoder = null;
protected MediaFormat mediaFormat;
protected UpstreamCallback mCallback;
protected Surface mSurface;
public MediaDecoder(String videoFilePath, Surface surface,UpstreamCallback callback) {
this.mVideoFilePath = videoFilePath;
this.mSurface = surface;
this.mCallback = callback;
}
@Override
public void run() {
// TODO Auto-generated method stub
super.run();
prepare();
}
public void prepare(){
try {
File videoFile = new File(mVideoFilePath);
mExtractor = new MediaExtractor();
mExtractor.setDataSource(videoFile.toString());
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
① 视频解码：
首先创建视频的解码器：
for (int i = 0; i < mExtractor.getTrackCount(); i++) {
MediaFormat format = mExtractor.getTrackFormat(i);
String mime = format.getString(MediaFormat.KEY_MIME);
if (mime.startsWith("video/")) {
mExtractor.selectTrack(i);
mDecoder = MediaCodec.createDecoderByType(mime);
if(mCallback != null){
mDecoder.configure(format, null, null, 0); //decode flag no output for surface
}else{
mDecoder.configure(format, mSurface, null, 0); //decode flag output to surface
}
break;
}
}
if (mDecoder == null) {
Log.e(TAG, "Can't find video info!");
return;
}
mDecoder.start();
当MediaCodec的解码buffer空闲时（mDecoder.dequeueInputBuffer），就可以把分离出的视频数据填充到buffer中（mDecoder.queueInputBuffer），让Decoder开始解码：
int inIndex = mDecoder.dequeueInputBuffer(TIME_US);
if (inIndex >= 0) {
ByteBuffer buffer = inputBuffers[inIndex];
int sampleSize = mExtractor.readSampleData(buffer, 0);
if (sampleSize < 0) {
// We shouldn't stop the playback at this point, just pass the EOS
// flag to mDecoder, we will get it again from the
// dequeueOutputBuffer
Log.d(TAG, "InputBuffer BUFFER_FLAG_END_OF_STREAM");
mDecoder.queueInputBuffer(inIndex, 0, 0, 0, MediaCodec.BUFFER_FLAG_END_OF_STREAM);
isEOS = true;
} else {
mDecoder.queueInputBuffer(inIndex, 0, sampleSize, mExtractor.getSampleTime(), 0);
mExtractor.advance();
}
}
Decoder解码出来的数据（mDecoder.dequeueOutputBuffer），解码的数据就可以做该做的处理，比如再编码，合成文件等。
BufferInfo info = new BufferInfo();
int outIndex = mDecoder.dequeueOutputBuffer(info, TIME_US);
switch (outIndex) {
case MediaCodec.INFO_OUTPUT_BUFFERS_CHANGED:
Log.d(TAG, "INFO_OUTPUT_BUFFERS_CHANGED");
outputBuffers = mDecoder.getOutputBuffers();
break;
case MediaCodec.INFO_OUTPUT_FORMAT_CHANGED:
Log.d(TAG, "New format " + mDecoder.getOutputFormat());
break;
case MediaCodec.INFO_TRY_AGAIN_LATER:
Log.d(TAG, "dequeueOutputBuffer timed out!");
break;
default:
//here erro?
Log.d(TAG, "outIndex:"+outIndex);
ByteBuffer buffer = outputBuffers[outIndex];
Log.d(TAG, "ByteBuffer limit:"+buffer.limit()+" info size:"+info.size);
final byte[] chunk = new byte[info.size];
buffer.get(chunk);
if(mCallback != null){
//mCallback.UpstreamCallback(chunk,info.size);
}
//clear buffer,otherwise get the same buffer which is the last buffer
buffer.clear();
if(DEBUG_VIDEO)Log.v(TAG, "We can't use this buffer but render it due to the API limit, " + buffer);
// We use a very simple clock to keep the video FPS, or the video
// playback will be too fast
while (info.presentationTimeUs / 1000 > System.currentTimeMillis() - startMs) {
try {
sleep(10);
} catch (InterruptedException e) {
e.printStackTrace();
break;
}
}
mDecoder.releaseOutputBuffer(outIndex, true);
break;
}
视频解码的完整代码：
public class VideoDecoder extends MediaDecoder{
private static final String TAG = “VideoDecode”;
private static final boolean DEBUG_VIDEO = false;
public VideoDecoder(String videoFilePath,Surface surface,UpstreamCallback callback){
super(videoFilePath, surface, callback);
}
@Override
public void run() {
// TODO Auto-generated method stub
super.run();
VideoDecodePrepare();
}
public void VideoDecodePrepare() {
try {
for (int i = 0; i < mExtractor.getTrackCount(); i++) {
MediaFormat format = mExtractor.getTrackFormat(i);
String mime = format.getString(MediaFormat.KEY_MIME);
if (mime.startsWith("video/")) {
mExtractor.selectTrack(i);
mDecoder = MediaCodec.createDecoderByType(mime);
if(mCallback != null){
mDecoder.configure(format, null, null, 0); //decode flag no output for surface
}else{
mDecoder.configure(format, mSurface, null, 0); //decode flag output to surface
}
break;
}
}
if (mDecoder == null) {
Log.e(TAG, "Can't find video info!");
return;
}
mDecoder.start();
ByteBuffer[] inputBuffers = mDecoder.getInputBuffers();
ByteBuffer[] outputBuffers = mDecoder.getOutputBuffers();
boolean isEOS = false;
long startMs = System.currentTimeMillis();
while (!Thread.interrupted()) {
if (!isEOS) {
int inIndex = mDecoder.dequeueInputBuffer(TIME_US);
if (inIndex >= 0) {
ByteBuffer buffer = inputBuffers[inIndex];
int sampleSize = mExtractor.readSampleData(buffer, 0);
if (sampleSize < 0) {
// We shouldn't stop the playback at this point, just pass the EOS
// flag to mDecoder, we will get it again from the
// dequeueOutputBuffer
Log.d(TAG, "InputBuffer BUFFER_FLAG_END_OF_STREAM");
mDecoder.queueInputBuffer(inIndex, 0, 0, 0, MediaCodec.BUFFER_FLAG_END_OF_STREAM);
isEOS = true;
} else {
mDecoder.queueInputBuffer(inIndex, 0, sampleSize, mExtractor.getSampleTime(), 0);
mExtractor.advance();
}
}
}
BufferInfo info = new BufferInfo();
int outIndex = mDecoder.dequeueOutputBuffer(info, TIME_US);
switch (outIndex) {
case MediaCodec.INFO_OUTPUT_BUFFERS_CHANGED:
Log.d(TAG, "INFO_OUTPUT_BUFFERS_CHANGED");
outputBuffers = mDecoder.getOutputBuffers();
break;
case MediaCodec.INFO_OUTPUT_FORMAT_CHANGED:
Log.d(TAG, "New format " + mDecoder.getOutputFormat());
break;
case MediaCodec.INFO_TRY_AGAIN_LATER:
Log.d(TAG, "dequeueOutputBuffer timed out!");
break;
default:
//here erro?
Log.d(TAG, "outIndex:"+outIndex);
ByteBuffer buffer = outputBuffers[outIndex];
Log.d(TAG, "ByteBuffer limit:"+buffer.limit()+" info size:"+info.size);
final byte[] chunk = new byte[info.size];
buffer.get(chunk);
if(mCallback != null){
//mCallback.UpstreamCallback(chunk,info.size);
}
//clear buffer,otherwise get the same buffer which is the last buffer
buffer.clear();
if(DEBUG_VIDEO)Log.v(TAG, "We can't use this buffer but render it due to the API limit, " + buffer);
// We use a very simple clock to keep the video FPS, or the video
// playback will be too fast
while (info.presentationTimeUs / 1000 > System.currentTimeMillis() - startMs) {
try {
sleep(10);
} catch (InterruptedException e) {
e.printStackTrace();
break;
}
}
mDecoder.releaseOutputBuffer(outIndex, true);
break;
}
// All decoded frames have been rendered, we can stop playing now
if ((info.flags & MediaCodec.BUFFER_FLAG_END_OF_STREAM) != 0) {
Log.d(TAG, "OutputBuffer BUFFER_FLAG_END_OF_STREAM");
break;
}
}
mDecoder.stop();
mDecoder.release();
mExtractor.release();
} catch (Exception ioe) {
Log.d(TAG,"failed init decoder", ioe);
}
}
注意video解码时，如果使用surface来输出，则outbuffer会被消耗掉，想要在视频输出的同时转码，建议使用OpenESGL来绘制窗口（这部分后面提供代码），保留原有buffer。
② 音频解码：
基本和视频解码的方式一样，只不过是通过MediaExtractor从文件中分离出音频，然后使用指定的音频MediaFormat来通知Decoder解码。
音频解码器的创建如下：
for (int i = 0; i < mExtractor.getTrackCount(); i++) {
MediaFormat format = mExtractor.getTrackFormat(i);
String mime = format.getString(MediaFormat.KEY_MIME);
if (mime.startsWith("audio/")) {
mExtractor.selectTrack(i);
mSampleRate = format.getInteger(MediaFormat.KEY_SAMPLE_RATE);
channel = format.getInteger(MediaFormat.KEY_CHANNEL_COUNT);
mDecoder = MediaCodec.createDecoderByType(mime);
mDecoder.configure(format, null, null, 0);
break;
}
}
if (mDecoder == null) {
Log.e(TAG, "Can't find audio info!");
return;
}
mDecoder.start();
在这里，我直接通过Android的AudioTrack来输出音频，完整代码如下：
public class AudioDecoder extends MediaDecoder {
private static final String TAG = “VideoDecode”;
private static final boolean DEBUG_AUDIO = false;
private int mSampleRate = 0;
private int channel = 0;
public AudioDecoder(String videoFilePath, Surface surface,UpstreamCallback callback) {
super(videoFilePath, surface, callback);
}
@Override
public void run() {
// TODO Auto-generated method stub
super.run();
AudioDecodePrepare();
}
public void AudioDecodePrepare() {
try {
for (int i = 0; i < mExtractor.getTrackCount(); i++) {
MediaFormat format = mExtractor.getTrackFormat(i);
String mime = format.getString(MediaFormat.KEY_MIME);
if (mime.startsWith("audio/")) {
mExtractor.selectTrack(i);
mSampleRate = format.getInteger(MediaFormat.KEY_SAMPLE_RATE);
channel = format.getInteger(MediaFormat.KEY_CHANNEL_COUNT);
mDecoder = MediaCodec.createDecoderByType(mime);
mDecoder.configure(format, null, null, 0);
break;
}
}
if (mDecoder == null) {
Log.e(TAG, "Can't find audio info!");
return;
}
mDecoder.start();
ByteBuffer[] inputBuffers = mDecoder.getInputBuffers();
ByteBuffer[] outputBuffers = mDecoder.getOutputBuffers();
BufferInfo info = new BufferInfo();
int buffsize = AudioTrack.getMinBufferSize(mSampleRate,
AudioFormat.CHANNEL_OUT_STEREO,
AudioFormat.ENCODING_PCM_16BIT);
AudioTrack audioTrack = new AudioTrack(AudioManager.STREAM_MUSIC,
mSampleRate, AudioFormat.CHANNEL_OUT_STEREO,
AudioFormat.ENCODING_PCM_16BIT, buffsize,
AudioTrack.MODE_STREAM);
audioTrack.play();
boolean isEOS = false;
long startMs = System.currentTimeMillis();
while (!Thread.interrupted()) {
if (!isEOS) {
int inIndex = mDecoder.dequeueInputBuffer(TIME_US);
if (inIndex >= 0) {
ByteBuffer buffer = inputBuffers[inIndex];
int sampleSize = mExtractor.readSampleData(buffer, 0);
if (sampleSize < 0) {
// We shouldn't stop the playback at this point,
// just pass the EOS
// flag to mediaDecoder, we will get it again from
// the
// dequeueOutputBuffer
Log.d(TAG, "InputBuffer BUFFER_FLAG_END_OF_STREAM");
mDecoder.queueInputBuffer(inIndex, 0, 0, 0,
MediaCodec.BUFFER_FLAG_END_OF_STREAM);
isEOS = true;
} else {
mDecoder.queueInputBuffer(inIndex, 0,
sampleSize, mExtractor.getSampleTime(), 0);
mExtractor.advance();
}
}
}
int outIndex = mDecoder.dequeueOutputBuffer(info, TIME_US);
switch (outIndex) {
case MediaCodec.INFO_OUTPUT_BUFFERS_CHANGED:
Log.d(TAG, "INFO_OUTPUT_BUFFERS_CHANGED");
outputBuffers = mDecoder.getOutputBuffers();
break;
case MediaCodec.INFO_OUTPUT_FORMAT_CHANGED:
MediaFormat format = mDecoder.getOutputFormat();
Log.d(TAG, "New format " + format);
audioTrack.setPlaybackRate(format
.getInteger(MediaFormat.KEY_SAMPLE_RATE));
break;
case MediaCodec.INFO_TRY_AGAIN_LATER:
Log.d(TAG, "dequeueOutputBuffer timed out!");
break;
default:
ByteBuffer buffer = outputBuffers[outIndex];
if(DEBUG_AUDIO)Log.v(TAG,"We can't use this buffer but render it due to the API limit, "+ buffer);
final byte[] chunk = new byte[info.size];
buffer.get(chunk);
if(mCallback != null){
mCallback.UpstreamCallback(chunk,info.size);
}
//clear buffer,otherwise get the same buffer which is the last buffer
buffer.clear();
// We use a very simple clock to keep the video FPS, or the
// audio playback will be too fast
while (info.presentationTimeUs / 1000 > System
.currentTimeMillis() - startMs) {
try {
sleep(10);
} catch (InterruptedException e) {
e.printStackTrace();
break;
}
}
// AudioTrack write data
audioTrack.write(chunk, info.offset, info.offset
+ info.size);
mDecoder.releaseOutputBuffer(outIndex, false);
break;
}
// All decoded frames have been rendered, we can stop playing now
if ((info.flags & MediaCodec.BUFFER_FLAG_END_OF_STREAM) != 0) {
Log.d(TAG, "OutputBuffer BUFFER_FLAG_END_OF_STREAM");
break;
}
}
mDecoder.stop();
mDecoder.release();
mExtractor.release();
audioTrack.stop();
audioTrack.release();
} catch (Exception ioe) {
throw new RuntimeException("failed init encoder", ioe);
}
}
}
通过以上处理，就可以使用硬解方案实现音视频播放了。
3.结束语
解码的知识先介绍这么多，下一篇会介绍MediaCodec来实现编码。感谢持续关注！