【Android】MediaCodec学习
在开源Android屏幕投屏代码scrcpy中，使用了MediaCodec去获取和display关联的surface的内容，再通过写fd的方式（socket等）传给PC端，
MediaCodec的处理看起来比较清楚，数据in和数据out
这里我们做另外一个尝试，读取手机中的mp4文件，显示到app的surface上，来学习MediaCodec的使用。
code
import android.media.MediaCodec;
import android.media.MediaExtractor;
import android.media.MediaFormat;
import android.os.Bundle;
import android.util.Log;
import android.view.Surface;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import androidx.appcompat.app.AppCompatActivity;
import java.io.IOException;
public class PlayActivity2 extends AppCompatActivity implements SurfaceHolder.Callback {
private static final int REQUEST_PERMISSION = 1;
private static final String SAMPLE_MP4_FILE = "/sdcard/Download/test.mp4";
private SurfaceView surfaceView;
private MediaExtractor mediaExtractor;
private MediaCodec mediaCodec;
private boolean isPlaying = false;
private String TAG = "testPlay";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_new);
Log.i(TAG, "onCreate");
surfaceView = findViewById(R.id.surfaceView);
surfaceView.getHolder().addCallback(this);
}
@Override
protected void onResume() {
super.onResume();
Log.i(TAG, "onResume");
if (!isPlaying) {
Log.i(TAG, "set isPlaying true");
isPlaying = true;
// playVideo();
}
}
@Override
protected void onPause() {
super.onPause();
if (isPlaying) {
Log.i(TAG, "onPause");
isPlaying = false;
releaseMediaCodec();
}
}
@Override
public void surfaceCreated(SurfaceHolder holder) {
isPlaying = true;
Log.i(TAG, "surfaceCreated");
//需要另外启动一个线程去处理
new Thread() {
@Override
public void run() {
playVideo();
}
}.start();
}
@Override
public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
Log.i(TAG, "surfaceChanged");
}
@Override
public void surfaceDestroyed(SurfaceHolder holder) {
Log.i(TAG, "surfaceDestroyed");
releaseMediaCodec();
}
private void playVideo() {
try {
Log.i(TAG, "playVideo");
mediaExtractor = new MediaExtractor();
mediaExtractor.setDataSource(SAMPLE_MP4_FILE);
int videoTrackIndex = getVideoTrackIndex();
if (videoTrackIndex >= 0) {
MediaFormat format = mediaExtractor.getTrackFormat(videoTrackIndex);
String mimeType = format.getString(MediaFormat.KEY_MIME);
mediaCodec = MediaCodec.createDecoderByType(mimeType);
Surface surface = surfaceView.getHolder().getSurface();
mediaCodec.configure(format, surface, null, 0);
mediaCodec.start();
Log.i(TAG, "mediaCodec.start");
decodeFrames(videoTrackIndex);
}
} catch (IOException e) {
e.printStackTrace();
}
}
private int getVideoTrackIndex() {
for (int i = 0; i < mediaExtractor.getTrackCount(); i++) {
MediaFormat format = mediaExtractor.getTrackFormat(i);
String mime = format.getString(MediaFormat.KEY_MIME);
if (mime.startsWith("video/")) {
mediaExtractor.selectTrack(i);
return i;
}
}
return -1;
}
private void decodeFrames(int videoTrackIndex) {
boolean isEOS = false;
final int TIMEOUT_US = 10000;
while (!Thread.interrupted()) {
if (!isPlaying)
break;
Log.i(TAG, "decodeFrames=, isPlaying=" + isPlaying);
int inputBufferIndex = mediaCodec.dequeueInputBuffer(TIMEOUT_US);
Log.i(TAG, "inputBufferIndex=" + inputBufferIndex);
if (inputBufferIndex >= 0) {
int sampleSize = mediaExtractor.readSampleData(mediaCodec.getInputBuffer(inputBufferIndex), 0);
if (sampleSize < 0) {
isEOS = true;
sampleSize = 0;
}
long presentationTimeUs = mediaExtractor.getSampleTime();
mediaCodec.queueInputBuffer(inputBufferIndex, 0, sampleSize, presentationTimeUs, isEOS ? MediaCodec.BUFFER_FLAG_END_OF_STREAM : 0);
if (!isEOS) {
Log.i(TAG, "mediaExtractor.advance()=" + sampleSize);
mediaExtractor.advance();
}
}
MediaCodec.BufferInfo bufferInfo = new MediaCodec.BufferInfo();
int outputBufferIndex = mediaCodec.dequeueOutputBuffer(bufferInfo, TIMEOUT_US);
Log.i(TAG, "outputBufferIndex======" + outputBufferIndex);
if (outputBufferIndex >= 0) {
mediaCodec.releaseOutputBuffer(outputBufferIndex, true);
if ((bufferInfo.flags & MediaCodec.BUFFER_FLAG_END_OF_STREAM) != 0) {
Log.i(TAG, "inputBufferIndex=, break");
break;
}
}
try {
Thread.sleep(10);
} catch (Exception e) {
}
}
}
private void releaseMediaCodec() {
if (mediaCodec != null) {
mediaCodec.stop();
mediaCodec.release();
mediaCodec = null;
}
if (mediaExtractor != null) {
mediaExtractor.release();
mediaExtractor = null;
}
}
}注意，这里的mp4文件放在了sdcard中，需要获取读取权限
public void requestPermission() {
if (Build.VERSION.SDK_INT >= 30) {
if (!Environment.isExternalStorageManager()) {
Intent intent = new Intent(Settings.ACTION_MANAGE_ALL_FILES_ACCESS_PERMISSION);
startActivity(intent);
return;
}
} else {
if (Build.VERSION.SDK_INT > Build.VERSION_CODES.M) {
if (PermissionChecker.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE) != PermissionChecker.PERMISSION_GRANTED) {
requestPermissions(requestPermission, requestPermissionCode);
}
}
}
}
activity_new.xml里定义一个SurfaceView
playVideo的处理需要在另外一个线程中执行，不能在主线程执行，不然只能显示停止的一个画面。
01-28 18:14:19.388 21442 21442 I testPlay: set isPlaying true
01-28 18:14:19.431 21442 21442 I testPlay: surfaceCreated
01-28 18:14:19.431 21442 21442 I testPlay: playVideo
01-28 18:14:19.479 21442 21442 I testPlay: mediaCodec.start
01-28 18:14:19.479 21442 21442 I testPlay: decodeFrames=, isPlaying=true
01-28 18:14:19.480 21442 21442 I testPlay: inputBufferIndex=2
01-28 18:14:19.483 21442 21442 I testPlay: mediaExtractor.advance()=85878
01-28 18:14:19.493 21442 21442 I testPlay: outputBufferIndex======-1
01-28 18:14:19.504 21442 21442 I testPlay: decodeFrames=, isPlaying=true
01-28 18:14:19.504 21442 21442 I testPlay: inputBufferIndex=3
01-28 18:14:19.507 21442 21442 I testPlay: mediaExtractor.advance()=3049在上述代码中，视频帧是通过 MediaCodec 解码后，使用 Surface 对象在 SurfaceView 上进行渲染的。
以下代码片段展示了视频帧的渲染过程：
MediaCodec.BufferInfo bufferInfo = new MediaCodec.BufferInfo();
int outputBufferIndex = mediaCodec.dequeueOutputBuffer(bufferInfo, TIMEOUT_US);
if (outputBufferIndex >= 0) {
mediaCodec.releaseOutputBuffer(outputBufferIndex, true);
if ((bufferInfo.flags & MediaCodec.BUFFER_FLAG_END_OF_STREAM) != 0) {
break;
}
}
在每次循环中，首先调用 dequeueOutputBuffer() 方法来获取可用的输出缓冲区的索引。如果返回的索引大于等于0，则说明有可用的输出缓冲区。
然后，通过调用 releaseOutputBuffer() 方法，将输出缓冲区的索引传递给 MediaCodec，通知它可以释放该缓冲区并将其渲染到指定的 Surface 上。
最后，检查 BufferInfo 的 flags 标志，如果标志中包含 BUFFER_FLAG_END_OF_STREAM，则说明已经解码并渲染完整个视频帧序列，可以退出循环。
在循环中不断解码和渲染视频帧，就可以在 SurfaceView 上实时显示视频内容。
参考资料
Android MediaCodec解析-CSDN博客