Stagefright框架中視頻播放流程

 

[整理]Stagefright框架中視頻播放流程

分類： android多媒體2011-10-27 14:42 3925人閱讀 評論(4) 收藏 舉報

框架codecaudiocallbackvideooutput

Stagefright框架中視頻播放流程


1.創建playerengine
// 設置數據源，以及 audio sink
MediaPlayer::SetDataSource(PATH_TO_FILE)-> 
MediaPlayerService::create->
MediaPlayerService::Client::setDataSource->
GetPlayerType->
MediaPlayerService:: Client::CreatePlayer->
StagefrightPlayer:: setAudioSink->
StagefrightPlayer:: setDataSource->
Create MediaPlayerImpl（AwesomePlayer）->
MediaPlayerImpl:: MediaPlayerImpl 
PlayerType:
PV_PLAYER--------------------(OpenCore中的PVPlayer，2.2之前的默認多媒體框架，從2.3開始android源碼中已經不存在了，變更爲Stagefright，但芯片廠商會添加進來。位於external/opencore目錄。)
SONIVOX_PLAYER----------- MidiFile()(MIDI 格式)
STAGEFRIGHT_PLAYER----- StagefrightPlayer
NU_PLAYER---------------------NuPlayer(流媒體播放器)
TEST_PLAYER------------------- TestPlayerStub (only for ‘test’ and ‘eng’build)
//以下爲與openMax插件的初始化連接。
AwesomePlayer:mClient.connect()->
OMXClient::connect->
MediaPlayerService::getOMX()->
OMXMaster::OMXMaster: addVendorPlugin ()->
addPlugin((*createOMXPlugin ())->
*createOMXPlugin (){
new TIOMXPlugin;
}


2.解析mUri指定的內容，根據header來確定對應的Extractor
AwesomePlayer:: prepare()
AwesomePlayer:: prepareAsync_l()->
在該函數中啓動mQueue,作爲EventHandler(stagefright使用event來進行驅動)
AwesomePlayer::finishSetDataSource_l()->
MediaExtractor::create(datasource)->


3.使用extractor對文件做A/V分離(mVideoTrack/mAudioTrack)
AwesomePlayer::setDataSource_l(extractor)->
AwesomePlayer::setVideoSource()->
AwesomePlayer::setAudioSource()->
mVideoTrack=source
mAudioTrack=source


4.根據mVideoTrace中編碼類型來選擇video_decoder(mVideoSource)
AwesomePlayer::initVideoDecoder()->
mVideoSource->start();(初始化解碼器)
OMXCodec::Create()->
根據編碼類型去匹配codecs,將softwareCodec優先放在matchCodecs前面，優先匹配，即優先建立softWareCodec
<MediaSource>softwareCodec=InstantiateSoftwareCodec(componentName, source)->
如果沒有匹配的softWareCodec則去調用hardware中實現的omx_codec
omx->allocateNode(componentName...)->
sp<OMXCodec> codec = new OMXCodec(~)->
observer->setCodec(codec)->
err = codec->configureCodec(meta, flags)->
return codec.


5.根據mAudioTrace中編碼類型來選擇audio_decoder(mAudioSource)
AwesomePlayer::initAudioDecoder()->
mAudioSource->start();(初始化解碼器)
OMXCodec::Create()->
根據編碼類型去匹配codecs,將softwareCodec優先放在matchCodecs前面，優先匹配，即優先建立softWareCodec
<MediaSource>softwareCodec=InstantiateSoftwareCodec(componentName, source)->
如果沒有匹配的softWareCodec則去調用Hardware中實現的omx_codec
omx->allocateNode(componentName...)->
sp<OMXCodec> codec = new OMXCodec(~)->
observer->setCodec(codec)->
err = codec->configureCodec(meta, flags)->
return codec.


6.創建AudioPlayer,解碼並開啓Audio output播放audio數據
AwesomePlayer::play_l->
mAudioPlayer = new AudioPlayer(mAudioSink, this);
mAudioPlayer->setSource(mAudioSource);
mAudioPlayer->start
mSource->read(&mFirstBuffer);(在audioplayer啓動過程中，會先讀取第一段需解碼後的資料。)
mAudioSink->open(..., &AudioPlayer::AudioSinkCallback, ...);
AudioSinkCallback{
me->fillBuffer(buffer, size)
}
開啓audio output，同時AudioPlayer將callback函數設給它，之後每次callback函數被調用，AudioPlayer便會去讀取Audio decoder解碼後的資料。)


7.根據Codec類型選擇Renderer
AwesomePlayer：:start->
postVideoEvent_l();
AwesomePlayer::onVideoEvent()->
mVideoSource->read()(&mVideoBuffer, &options)->
AwesomePlayer::initRenderer_l()->
判斷Codec類型，
HardWare Codec：
mVideoRenderer =new AwesomeNativeWindowRenderer(mSurface, rotationDegrees);
AwesomeNativeWindowRenderer::render()(hook Called by EGL)->
HardWare Codec不需要進行ColorConvert操作，直接push到NativeWindow
SoftWare Codec：
mVideoRenderer = new AwesomeLocalRenderer(mSurface, meta)->
mVideoRenderer = new SoftwareRenderer()->
SoftwareRenderer::render()->
AwesomePlayer::onVideoEvent()->
[Check Timestamp]
mVideoRenderer->render(mVideoBuffer);


8.Audio和Video同步
Stagefright中Audio由CallBack驅動數據流，Video則在OnVideoEvent中獲取Audio的timeStamp，進行同步。
Audio::fillBuffer()->     
mPositionTimeMediaUs爲資料中的timestamp,
mPositionTimeRealUs爲播放資料的實際時間。
 AwesomePlayer::onVideoEvent()->
mTimeSourceDeltaUs = realTimeUs- mediaTimeUs