video/audio playback:prepare & start

最新推荐文章于 2024-03-05 18:39:41 发布

转载最新推荐文章于 2024-03-05 18:39:41 发布 · 875 阅读

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#playback #null #audio #video #buffer #callback

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本文详细解析了Android系统中音视频播放的过程，包括从准备阶段到解码播放的全过程。重点介绍了AwesomePlayer如何处理不同类型的URL，如HTTP、RTSP等，并针对mAudioTrack和mVideoTrack进行分离和解码。

prepare:启动mQueue，对http://，rtsp://gtalk/，fmradio://rx 之类的url进行mAudioTrack/mVideoTrack分离，并根据mAudioTrack/mVideoTrack编码类型选择相应的decode

1.framework/base/media/libmediaplayerservice/MediaPlayerService.cpp

status_t MediaPlayerService::Client::prepareAsync()

{….

sp<MediaPlayerBase> p = getPlayer(); …….. setDataSource时创建的stagefrightplayer

if (p == 0) return UNKNOWN_ERROR;

status_t ret = p->prepareAsync();

……

return ret;

}

2.framework/base/media/libmediaplayerservice/stagefrightplayer

status_t StagefrightPlayer::prepareAsync() {

return mPlayer->prepareAsync();…………mPlayer--->AwesomePlayer

}

3:framework/base/media/libstagefright/awesomePlayer

status_t AwesomePlayer::prepareAsync() {

…….

return prepareAsync_l();

}

启动mQueue，onPrepareAsyncEvent被触发

status_t AwesomePlayer::prepareAsync_l() {……

if (!mQueueStarted) {

mQueue.start();

mQueueStarted = true;

}

….

mAsyncPrepareEvent = new AwesomeEvent(

this, &AwesomePlayer::onPrepareAsyncEvent);

mQueue.postEvent(mAsyncPrepareEvent);

return OK;

}

void AwesomePlayer::onPrepareAsyncEvent() {

….

if (mUri.size() > 0) {

status_t err = finishSetDataSource_l();………….对http://之类的url进行mAudioTrack/mVideoTrack分离

if (mVideoTrack != NULL && mVideoSource == NULL) {

status_t err = initVideoDecoder();……………………decode video

}

if (mAudioTrack != NULL && mAudioSource == NULL) {

status_t err = initAudioDecoder();…………………….decode audio

return;

}

}

if (mCachedSource != NULL || mRTSPController != NULL) {

postBufferingEvent_l();………………..触发mBufferingEvent，对应的实现在void AwesomePlayer::onBufferingUpdate()

}

}

start：解码并播放

1,framework/base/media/libmedia/mediaPlayer.cpp

status_t MediaPlayer::start()

{……

if ( (mPlayer != 0) && ( mCurrentState & ( MEDIA_PLAYER_PREPARED |

MEDIA_PLAYER_PLAYBACK_COMPLETE | MEDIA_PLAYER_PAUSED ) ) ) {

mPlayer->setLooping(mLoop);

mPlayer->setVolume(mLeftVolume, mRightVolume);

mPlayer->setAuxEffectSendLevel(mSendLevel);

mCurrentState = MEDIA_PLAYER_STARTED;

status_t ret = mPlayer->start();

……….

}

2,framework/base/media/libmediaPlayerService /mediaPlayerService.cpp

status_t MediaPlayerService::Client::start()

{..

sp<MediaPlayerBase> p = getPlayer();

…

p->setLooping(mLoop);

return p->start();

}

3,framework/base/media/libmediaPlayerService/stagefrightplayer.cpp

status_t StagefrightPlayer::start() {

return mPlayer->play();

}

4,framework/base/media/libstagefright/awesomePlayer.cpp

tatus_t AwesomePlayer::play() {

………..

return play_l();

}

status_t AwesomePlayer::play_l() {

……

if (mVideoSource != NULL) {

// Kick off video playback

postVideoEvent_l();……..把videoEvent放入mQueue中

…

}

开始解码播放，并由mVideoRenderer输出，video playback 完成

void AwesomePlayer::onVideoEvent() {……………

status_t err = mVideoSource->read(&mVideoBuffer[mVideoQueueBack], &options);

……….

if (mVideoRenderer != NULL) {

mVideoRenderer->render(mVideoBuffer[mVideoQueueBack]);

}

…..

postVideoEvent_l();

}

audio playerback

1,framework/base/media/libstagefright/awesomePlayer.cpp

status_t AwesomePlayer::play_l() {

if (mAudioSource != NULL) {

if (mAudioPlayer == NULL) {

if (mAudioSink != NULL) {

mWatchForAudioSeekComplete = false;

mAudioPlayer = new AudioPlayer(mAudioSink, this);

mAudioPlayer->setSource(mAudioSource);

…………..

}

}

status_t err = mAudioPlayer->start(

true /* sourceAlreadyStarted */);

………………..

}

2,framework/base/media/libstagefright/audioplayer.cpp

读第一手解析的数据，并开启audio output

status_t AudioPlayer::start(bool sourceAlreadyStarted) {

if (mAudioSink.get() != NULL) {

status_t err = mAudioSink->open(

mSampleRate, numChannels, AudioSystem::PCM_16_BIT,

DEFAULT_AUDIOSINK_BUFFERCOUNT,

&AudioPlayer::AudioSinkCallback, this);

……

mAudioSink->start();

} else {

mAudioTrack = new AudioTrack(

AudioSystem::MUSIC, mSampleRate, AudioSystem::PCM_16_BIT,

(numChannels == 2)

? AudioSystem::CHANNEL_OUT_STEREO

: AudioSystem::CHANNEL_OUT_MONO,

0, 0, &AudioCallback, this, 0);

….

mAudioTrack->start();

}

mStarted = true;

return OK;

}

开启audio output 时后把AudioSinkCallback传给它，每当调用callback时，audioplayer都回去decode 获取解码后的数据

size_t AudioPlayer::AudioSinkCallback(

MediaPlayerBase::AudioSink *audioSink,

void *buffer, size_t size, void *cookie) {

AudioPlayer *me = (AudioPlayer *)cookie;

return me->fillBuffer(buffer, size);

}

size_t AudioPlayer::fillBuffer(void *data, size_t size) {

…..

err = mSource->read(&mInputBuffer, &options);

…..

memcpy((char *)data + size_done,

(const char *)mInputBuffer->data() + mInputBuffer->range_offset(),

copy);

…….

return size_done;

}