今天我们来讲讲如何使用MediaExtractor + MediaCodec实现一个简易的播放器。
我们都知道MediaCodec是Android 环境下的硬编解码器，而MediaExtractor 则给我们提供了读取视频等媒体文件信息的功能。
如何使用MediaExtractor 和 MediaCodec 实现一个简易的播放器呢？其实并不难，整体的流程如下：
1、创建视频解码线程
2、创建音频解码线程
3、开始视频解码
4、开始音频解码
5、解码播放延时同步
首先，我们来看看视频解码线程如何实现：
视频解码的大体流程
1、获取视频的轨道信息
2、创建MediaCodec
3、将解复用得到的数据传递给解码器
4、获取解码后的数据
5、显示输出
实现代码如下：
/**
* 视频解码线程
*/
private class VideoDecodeThread extends Thread {
@Override
public void run() {
MediaExtractor videoExtractor = new MediaExtractor();
MediaCodec videoCodec = null;
try {
videoExtractor.setDataSource(filePath);
} catch (IOException e) {
e.printStackTrace();
}
int videoTrackIndex;
// 获取视频所在轨道
videoTrackIndex = getTrackIndex(videoExtractor, "video/");
if (videoTrackIndex >= 0) {
MediaFormat mediaFormat = videoExtractor.getTrackFormat(videoTrackIndex);
int width = mediaFormat.getInteger(MediaFormat.KEY_WIDTH);
int height = mediaFormat.getInteger(MediaFormat.KEY_HEIGHT);
float time = mediaFormat.getLong(MediaFormat.KEY_DURATION) / 1000000;
if (mListener != null) {
mListener.videoAspect(width, height, time);
}
videoExtractor.selectTrack(videoTrackIndex);
try {
videoCodec = MediaCodec.createDecoderByType(mediaFormat.getString(MediaFormat.KEY_MIME));
videoCodec.configure(mediaFormat, surface, null, 0);
} catch (IOException e) {
e.printStackTrace();
}
}
if (videoCodec == null) {
if (VERBOSE) {
Log.d(TAG, "video decoder is unexpectedly null");
}
return;
}
videoCodec.start();
MediaCodec.BufferInfo videoBufferInfo = new MediaCodec.BufferInfo();
ByteBuffer[] inputBuffers = videoCodec.getInputBuffers();
boolean isVideoEOS = false;
long startMs = System.currentTimeMillis();
while (!Thread.interrupted() && !cancel) {
if (isPlaying) {
// 暂停
if (isPause) {
continue;
}
// 将资源传递到解码器
if (!isVideoEOS) {
isVideoEOS = decodeMediaData(videoExtractor, videoCodec, inputBuffers);
}
// 获取解码后的数据
int outputBufferIndex = videoCodec.dequeueOutputBuffer(videoBufferInfo, TIMEOUT_US);
switch (outputBufferIndex) {
case MediaCodec.INFO_OUTPUT_FORMAT_CHANGED:
if (VERBOSE) {
Log.d(TAG, "INFO_OUTPUT_FORMAT_CHANGED");
}
break;
case MediaCodec.INFO_TRY_AGAIN_LATER:
if (VERBOSE) {
Log.d(TAG, "INFO_TRY_AGAIN_LATER");
}
break;
case MediaCodec.INFO_OUTPUT_BUFFERS_CHANGED:
if (VERBOSE) {
Log.d(TAG, "INFO_OUTPUT_BUFFERS_CHANGED");
}
break;
default:
// 延迟解码
decodeDelay(videoBufferInfo, startMs);
// 释放资源
videoCodec.releaseOutputBuffer(outputBufferIndex, true);
break;
}
// 结尾
if ((videoBufferInfo.flags & MediaCodec.BUFFER_FLAG_END_OF_STREAM) != 0) {
Log.v(TAG, "buffer stream end");
break;
}
}
}
// 释放解码器
videoCodec.stop();
videoCodec.release();
videoExtractor.release();
}
}
其中，解复用的方法如下：
/**
* 解复用，得到需要解码的数据
* @param extractor
* @param decoder
* @param inputBuffers
* @return
*/
private static boolean decodeMediaData(MediaExtractor extractor, MediaCodec decoder, ByteBuffer[] inputBuffers) {
boolean isMediaEOS = false;
int inputBufferIndex = decoder.dequeueInputBuffer(TIMEOUT_US);
if (inputBufferIndex >= 0) {
ByteBuffer inputBuffer = inputBuffers[inputBufferIndex];
int sampleSize = extractor.readSampleData(inputBuffer, 0);
if (sampleSize < 0) {
decoder.queueInputBuffer(inputBufferIndex, 0, 0, 0, MediaCodec.BUFFER_FLAG_END_OF_STREAM);
isMediaEOS = true;
if (VERBOSE) {
Log.d(TAG, "end of stream");
}
} else {
decoder.queueInputBuffer(inputBufferIndex, 0, sampleSize, extractor.getSampleTime(), 0);
extractor.advance();
}
}
return isMediaEOS;
}
解码延时实现如下：
/**
* 解码延时
* @param bufferInfo
* @param startMillis
*/
private void decodeDelay(MediaCodec.BufferInfo bufferInfo, long startMillis) {
while (bufferInfo.presentationTimeUs / 1000 > System.currentTimeMillis() - startMillis) {
try {
Thread.sleep(10);
} catch (InterruptedException e) {
e.printStackTrace();
break;
}
}
}
同样，音频解码线程跟视频解码线程大体类似。这里不做详细介绍，直接上代码：
/**
* 音频解码线程
*/
private class AudioDecodeThread extends Thread {
private int mInputBufferSize;
private AudioTrack audioTrack;
@Override
public void run() {
MediaExtractor audioExtractor = new MediaExtractor();
MediaCodec audioCodec = null;
try {
audioExtractor.setDataSource(filePath);
} catch (IOException e) {
e.printStackTrace();
}
for (int i = 0; i < audioExtractor.getTrackCount(); i++) {
MediaFormat mediaFormat = audioExtractor.getTrackFormat(i);
String mime = mediaFormat.getString(MediaFormat.KEY_MIME);
if (mime.startsWith("audio/")) {
audioExtractor.selectTrack(i);
int audioChannels = mediaFormat.getInteger(MediaFormat.KEY_CHANNEL_COUNT);
int audioSampleRate = mediaFormat.getInteger(MediaFormat.KEY_SAMPLE_RATE);
int minBufferSize = AudioTrack.getMinBufferSize(audioSampleRate,
(audioChannels == 1 ? AudioFormat.CHANNEL_OUT_MONO : AudioFormat.CHANNEL_OUT_STEREO),
AudioFormat.ENCODING_PCM_16BIT);
int maxInputSize = mediaFormat.getInteger(MediaFormat.KEY_MAX_INPUT_SIZE);
mInputBufferSize = minBufferSize > 0 ? minBufferSize * 4 : maxInputSize;
int frameSizeInBytes = audioChannels * 2;
mInputBufferSize = (mInputBufferSize / frameSizeInBytes) * frameSizeInBytes;
audioTrack = new AudioTrack(AudioManager.STREAM_MUSIC,
audioSampleRate,
(audioChannels == 1 ? AudioFormat.CHANNEL_OUT_MONO : AudioFormat.CHANNEL_OUT_STEREO),
AudioFormat.ENCODING_PCM_16BIT,
mInputBufferSize,
AudioTrack.MODE_STREAM);
audioTrack.play();
try {
audioCodec = MediaCodec.createDecoderByType(mime);
audioCodec.configure(mediaFormat, null, null, 0);
} catch (IOException e) {
e.printStackTrace();
}
break;
}
}
if (audioCodec == null) {
if (VERBOSE) {
Log.d(TAG, "audio decoder is unexpectedly null");
}
return;
}
audioCodec.start();
final ByteBuffer[] buffers = audioCodec.getOutputBuffers();
int sz = buffers[0].capacity();
if (sz <= 0) {
sz = mInputBufferSize;
}
byte[] mAudioOutTempBuf = new byte[sz];
MediaCodec.BufferInfo audioBufferInfo = new MediaCodec.BufferInfo();
ByteBuffer[] inputBuffers = audioCodec.getInputBuffers();
ByteBuffer[] outputBuffers = audioCodec.getOutputBuffers();
boolean isAudioEOS = false;
long startMs = System.currentTimeMillis();
while (!Thread.interrupted() && !cancel) {
if (isPlaying) {
// 暂停
if (isPause) {
continue;
}
// 解码
if (!isAudioEOS) {
isAudioEOS = decodeMediaData(audioExtractor, audioCodec, inputBuffers);
}
// 获取解码后的数据
int outputBufferIndex = audioCodec.dequeueOutputBuffer(audioBufferInfo, TIMEOUT_US);
switch (outputBufferIndex) {
case MediaCodec.INFO_OUTPUT_FORMAT_CHANGED:
if (VERBOSE) {
Log.d(TAG, "INFO_OUTPUT_FORMAT_CHANGED");
}
break;
case MediaCodec.INFO_TRY_AGAIN_LATER:
if (VERBOSE) {
Log.d(TAG, "INFO_TRY_AGAIN_LATER");
}
break;
case MediaCodec.INFO_OUTPUT_BUFFERS_CHANGED:
outputBuffers = audioCodec.getOutputBuffers();
if (VERBOSE) {
Log.d(TAG, "INFO_OUTPUT_BUFFERS_CHANGED");
}
break;
default:
ByteBuffer outputBuffer = outputBuffers[outputBufferIndex];
// 延时解码，跟视频时间同步
decodeDelay(audioBufferInfo, startMs);
// 如果解码成功，则将解码后的音频PCM数据用AudioTrack播放出来
if (audioBufferInfo.size > 0) {
if (mAudioOutTempBuf.length < audioBufferInfo.size) {
mAudioOutTempBuf = new byte[audioBufferInfo.size];
}
outputBuffer.position(0);
outputBuffer.get(mAudioOutTempBuf, 0, audioBufferInfo.size);
outputBuffer.clear();
if (audioTrack != null)
audioTrack.write(mAudioOutTempBuf, 0, audioBufferInfo.size);
}
// 释放资源
audioCodec.releaseOutputBuffer(outputBufferIndex, false);
break;
}
// 结尾了
if ((audioBufferInfo.flags & MediaCodec.BUFFER_FLAG_END_OF_STREAM) != 0) {
if (VERBOSE) {
Log.d(TAG, "BUFFER_FLAG_END_OF_STREAM");
}
break;
}
}
}
// 释放MediaCode 和AudioTrack
audioCodec.stop();
audioCodec.release();
audioExtractor.release();
audioTrack.stop();
audioTrack.release();
}
}
至此，我们就将简易播放器的核心功能实现了，完整的实现代码如下：
public class SimplePlayer {
private static final String TAG = "Player";
private static final boolean VERBOSE = false;
private static final long TIMEOUT_US = 10000;
private IPlayStateListener mListener;
private VideoDecodeThread mVideoDecodeThread;
private AudioDecodeThread mAudioDecodeThread;
private boolean isPlaying;
private boolean isPause;
private String filePath;
private Surface surface;
// 是否取消播放线程
private boolean cancel = false;
public SimplePlayer(Surface surface, String filePath) {
this.surface = surface;
this.filePath = filePath;
isPlaying = false;
isPause = false;
}
/**
* 设置回调
* @param mListener
*/
public void setPlayStateListener(IPlayStateListener mListener) {
this.mListener = mListener;
}
/**
* 是否处于播放状态
* @return
*/
public boolean isPlaying() {
return isPlaying && !isPause;
}
/**
* 开始播放
*/
public void play() {
isPlaying = true;
if (mVideoDecodeThread == null) {
mVideoDecodeThread = new VideoDecodeThread();
mVideoDecodeThread.start();
}
if (mAudioDecodeThread == null) {
mAudioDecodeThread = new AudioDecodeThread();
mAudioDecodeThread.start();
}
}
/**
* 暂停
*/
public void pause() {
isPause = true;
}
/**
* 继续播放
*/
public void continuePlay() {
isPause = false;
}
/**
* 停止播放
*/
public void stop() {
isPlaying = false;
}
/**
* 销毁
*/
public void destroy() {
stop();
if (mAudioDecodeThread != null) {
mAudioDecodeThread.interrupt();
}
if (mVideoDecodeThread != null) {
mVideoDecodeThread.interrupt();
}
}
/**
* 解复用，得到需要解码的数据
* @param extractor
* @param decoder
* @param inputBuffers
* @return
*/
private static boolean decodeMediaData(MediaExtractor extractor, MediaCodec decoder, ByteBuffer[] inputBuffers) {
boolean isMediaEOS = false;
int inputBufferIndex = decoder.dequeueInputBuffer(TIMEOUT_US);
if (inputBufferIndex >= 0) {
ByteBuffer inputBuffer = inputBuffers[inputBufferIndex];
int sampleSize = extractor.readSampleData(inputBuffer, 0);
if (sampleSize < 0) {
decoder.queueInputBuffer(inputBufferIndex, 0, 0, 0, MediaCodec.BUFFER_FLAG_END_OF_STREAM);
isMediaEOS = true;
if (VERBOSE) {
Log.d(TAG, "end of stream");
}
} else {
decoder.queueInputBuffer(inputBufferIndex, 0, sampleSize, extractor.getSampleTime(), 0);
extractor.advance();
}
}
return isMediaEOS;
}
/**
* 解码延时
* @param bufferInfo
* @param startMillis
*/
private void decodeDelay(MediaCodec.BufferInfo bufferInfo, long startMillis) {
while (bufferInfo.presentationTimeUs / 1000 > System.currentTimeMillis() - startMillis) {
try {
Thread.sleep(10);
} catch (InterruptedException e) {
e.printStackTrace();
break;
}
}
}
/**
* 获取媒体类型的轨道
* @param extractor
* @param mediaType
* @return
*/
private static int getTrackIndex(MediaExtractor extractor, String mediaType) {
int trackIndex = -1;
for (int i = 0; i < extractor.getTrackCount(); i++) {
MediaFormat mediaFormat = extractor.getTrackFormat(i);
String mime = mediaFormat.getString(MediaFormat.KEY_MIME);
if (mime.startsWith(mediaType)) {
trackIndex = i;
break;
}
}
return trackIndex;
}
/**
* 视频解码线程
*/
private class VideoDecodeThread extends Thread {
@Override
public void run() {
MediaExtractor videoExtractor = new MediaExtractor();
MediaCodec videoCodec = null;
try {
videoExtractor.setDataSource(filePath);
} catch (IOException e) {
e.printStackTrace();
}
int videoTrackIndex;
// 获取视频所在轨道
videoTrackIndex = getTrackIndex(videoExtractor, "video/");
if (videoTrackIndex >= 0) {
MediaFormat mediaFormat = videoExtractor.getTrackFormat(videoTrackIndex);
int width = mediaFormat.getInteger(MediaFormat.KEY_WIDTH);
int height = mediaFormat.getInteger(MediaFormat.KEY_HEIGHT);
float time = mediaFormat.getLong(MediaFormat.KEY_DURATION) / 1000000;
if (mListener != null) {
mListener.videoAspect(width, height, time);
}
videoExtractor.selectTrack(videoTrackIndex);
try {
videoCodec = MediaCodec.createDecoderByType(mediaFormat.getString(MediaFormat.KEY_MIME));
videoCodec.configure(mediaFormat, surface, null, 0);
} catch (IOException e) {
e.printStackTrace();
}
}
if (videoCodec == null) {
if (VERBOSE) {
Log.d(TAG, "video decoder is unexpectedly null");
}
return;
}
videoCodec.start();
MediaCodec.BufferInfo videoBufferInfo = new MediaCodec.BufferInfo();
ByteBuffer[] inputBuffers = videoCodec.getInputBuffers();
boolean isVideoEOS = false;
long startMs = System.currentTimeMillis();
while (!Thread.interrupted() && !cancel) {
if (isPlaying) {
// 暂停
if (isPause) {
continue;
}
// 将资源传递到解码器
if (!isVideoEOS) {
isVideoEOS = decodeMediaData(videoExtractor, videoCodec, inputBuffers);
}
// 获取解码后的数据
int outputBufferIndex = videoCodec.dequeueOutputBuffer(videoBufferInfo, TIMEOUT_US);
switch (outputBufferIndex) {
case MediaCodec.INFO_OUTPUT_FORMAT_CHANGED:
if (VERBOSE) {
Log.d(TAG, "INFO_OUTPUT_FORMAT_CHANGED");
}
break;
case MediaCodec.INFO_TRY_AGAIN_LATER:
if (VERBOSE) {
Log.d(TAG, "INFO_TRY_AGAIN_LATER");
}
break;
case MediaCodec.INFO_OUTPUT_BUFFERS_CHANGED:
if (VERBOSE) {
Log.d(TAG, "INFO_OUTPUT_BUFFERS_CHANGED");
}
break;
default:
// 延迟解码
decodeDelay(videoBufferInfo, startMs);
// 释放资源
videoCodec.releaseOutputBuffer(outputBufferIndex, true);
break;
}
// 结尾
if ((videoBufferInfo.flags & MediaCodec.BUFFER_FLAG_END_OF_STREAM) != 0) {
Log.v(TAG, "buffer stream end");
break;
}
}
}
// 释放解码器
videoCodec.stop();
videoCodec.release();
videoExtractor.release();
}
}
/**
* 音频解码线程
*/
private class AudioDecodeThread extends Thread {
private int mInputBufferSize;
private AudioTrack audioTrack;
@Override
public void run() {
MediaExtractor audioExtractor = new MediaExtractor();
MediaCodec audioCodec = null;
try {
audioExtractor.setDataSource(filePath);
} catch (IOException e) {
e.printStackTrace();
}
for (int i = 0; i < audioExtractor.getTrackCount(); i++) {
MediaFormat mediaFormat = audioExtractor.getTrackFormat(i);
String mime = mediaFormat.getString(MediaFormat.KEY_MIME);
if (mime.startsWith("audio/")) {
audioExtractor.selectTrack(i);
int audioChannels = mediaFormat.getInteger(MediaFormat.KEY_CHANNEL_COUNT);
int audioSampleRate = mediaFormat.getInteger(MediaFormat.KEY_SAMPLE_RATE);
int minBufferSize = AudioTrack.getMinBufferSize(audioSampleRate,
(audioChannels == 1 ? AudioFormat.CHANNEL_OUT_MONO : AudioFormat.CHANNEL_OUT_STEREO),
AudioFormat.ENCODING_PCM_16BIT);
int maxInputSize = mediaFormat.getInteger(MediaFormat.KEY_MAX_INPUT_SIZE);
mInputBufferSize = minBufferSize > 0 ? minBufferSize * 4 : maxInputSize;
int frameSizeInBytes = audioChannels * 2;
mInputBufferSize = (mInputBufferSize / frameSizeInBytes) * frameSizeInBytes;
audioTrack = new AudioTrack(AudioManager.STREAM_MUSIC,
audioSampleRate,
(audioChannels == 1 ? AudioFormat.CHANNEL_OUT_MONO : AudioFormat.CHANNEL_OUT_STEREO),
AudioFormat.ENCODING_PCM_16BIT,
mInputBufferSize,
AudioTrack.MODE_STREAM);
audioTrack.play();
try {
audioCodec = MediaCodec.createDecoderByType(mime);
audioCodec.configure(mediaFormat, null, null, 0);
} catch (IOException e) {
e.printStackTrace();
}
break;
}
}
if (audioCodec == null) {
if (VERBOSE) {
Log.d(TAG, "audio decoder is unexpectedly null");
}
return;
}
audioCodec.start();
final ByteBuffer[] buffers = audioCodec.getOutputBuffers();
int sz = buffers[0].capacity();
if (sz <= 0) {
sz = mInputBufferSize;
}
byte[] mAudioOutTempBuf = new byte[sz];
MediaCodec.BufferInfo audioBufferInfo = new MediaCodec.BufferInfo();
ByteBuffer[] inputBuffers = audioCodec.getInputBuffers();
ByteBuffer[] outputBuffers = audioCodec.getOutputBuffers();
boolean isAudioEOS = false;
long startMs = System.currentTimeMillis();
while (!Thread.interrupted() && !cancel) {
if (isPlaying) {
// 暂停
if (isPause) {
continue;
}
// 解码
if (!isAudioEOS) {
isAudioEOS = decodeMediaData(audioExtractor, audioCodec, inputBuffers);
}
// 获取解码后的数据
int outputBufferIndex = audioCodec.dequeueOutputBuffer(audioBufferInfo, TIMEOUT_US);
switch (outputBufferIndex) {
case MediaCodec.INFO_OUTPUT_FORMAT_CHANGED:
if (VERBOSE) {
Log.d(TAG, "INFO_OUTPUT_FORMAT_CHANGED");
}
break;
case MediaCodec.INFO_TRY_AGAIN_LATER:
if (VERBOSE) {
Log.d(TAG, "INFO_TRY_AGAIN_LATER");
}
break;
case MediaCodec.INFO_OUTPUT_BUFFERS_CHANGED:
outputBuffers = audioCodec.getOutputBuffers();
if (VERBOSE) {
Log.d(TAG, "INFO_OUTPUT_BUFFERS_CHANGED");
}
break;
default:
ByteBuffer outputBuffer = outputBuffers[outputBufferIndex];
// 延时解码，跟视频时间同步
decodeDelay(audioBufferInfo, startMs);
// 如果解码成功，则将解码后的音频PCM数据用AudioTrack播放出来
if (audioBufferInfo.size > 0) {
if (mAudioOutTempBuf.length < audioBufferInfo.size) {
mAudioOutTempBuf = new byte[audioBufferInfo.size];
}
outputBuffer.position(0);
outputBuffer.get(mAudioOutTempBuf, 0, audioBufferInfo.size);
outputBuffer.clear();
if (audioTrack != null)
audioTrack.write(mAudioOutTempBuf, 0, audioBufferInfo.size);
}
// 释放资源
audioCodec.releaseOutputBuffer(outputBufferIndex, false);
break;
}
// 结尾了
if ((audioBufferInfo.flags & MediaCodec.BUFFER_FLAG_END_OF_STREAM) != 0) {
if (VERBOSE) {
Log.d(TAG, "BUFFER_FLAG_END_OF_STREAM");
}
break;
}
}
}
// 释放MediaCode 和AudioTrack
audioCodec.stop();
audioCodec.release();
audioExtractor.release();
audioTrack.stop();
audioTrack.release();
}
}
}
那么这样还存在什么问题呢？ 那就是同步和是否支持媒体流的问题了。上面的代码只是简单地获取本地视频文件，分别将视频帧解码显示和音频帧解码播放出来，还存在同步问题。同步无非就是追及过程，当视频帧播放快了，则等待音频帧播放完或者加快、舍弃音频帧，当音频播放快了，则判断是否需要加快视频帧的播放甚至舍弃视频帧。这里不同的同步方式，产生了几种不同的同步策略，分别是视频同步到音频、音频同步到视频、以外部时钟作为同步基准。详细的策略可以参考ffplay的源码。还有就是媒体流的支持问题，目前市面上的播放都是支持流媒体播放的，媒体流肯定要支持的，使用MediaCodec做播放器，在应对网络抖动方面还是比不上基于FFmpeg的软解码的播放器的。如果想要做商用的播放器，个人建议还是使用FFmpeg实现会好很多，可参考的资料也更多，遇到什么问题可以请教有经验的前辈，帮助我们少踩坑。
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