重点研究libstagefright
AwesomePlayer.cpp
MediaExtractor.cpp
OpenMAX
Stagefright在Android中的位置
Stagefright所涵盖的模块
在Java播放视频，我们一般会这样写：
MediaPlayer mp = new MediaPlayer();
mp.setDataSource(PATH_TO_FILE); ...... (1)
mp.prepare(); ........................ (2)(3)
mp.start(); .......................... (4)
在Stagefright中有对应的处理：
** AwesomePlayer.cpp**中
- 指定文件路径给mUri
status_t AwesomePlayer::setDataSource(const char* uri, ...)
{
return setDataSource_l(uri, ...);
}
status_t AwesomePlayer::setDataSource_l(const char* uri, ...)
{
mUri = uri;
}
- prepare()启动mQueue作为event handler
status_t AwesomePlayer::prepare(){
return prepare_l();
}
status_t AwesomePlayer::prepare_l()
{
prepareAsync_l();
while (mFlags & PREPARING)
{
mPreparedCondition.wait(mLock);
}
}
status_t AwesomePlayer::prepareAsync_l()
{
mQueue.start(); mFlags |= PREPARING;
mAsyncPrepareEvent = new AwesomeEvent(this, &AwesomePlayer::onPrepareAsyncEvent);
mQueue.postEvent(mAsyncPrepareEvent);
}
- onPrepareAsyncEvent被触发
void AwesomePlayer::onPrepareAsyncEvent()
{
finishSetDataSource_l();
initVideoDecoder(); ......
initAudioDecoder();
}
status_t AwesomePlayer::finishSetDataSource_l()
{
dataSource = DataSource::CreateFromURI(mUri.string(), ...);
sp<MediaExtractor> extractor = MediaExtractor::Create(dataSource);
return setDataSource_l(extractor);
}
- 由数据源DataSource生成MediaExtractor（在MediaExtractor.cpp中）
解析mUri所指定的文件，并根据其header来选择对应的extractor
sp<MediaExtractor> MediaExtractor::Create(const sp<DataSource> &source, ...)
{
......
MediaExtractor *ret = NULL;
if (!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_MPEG4)
|| !strcasecmp(mime, "audio/mp4")) {
ret = new MPEG4Extractor(source);
} else if (!strcasecmp(mime, MEDIA_MIMETYPE_AUDIO_MPEG)) {
ret = new MP3Extractor(source, meta);
} else if (!strcasecmp(mime, MEDIA_MIMETYPE_AUDIO_AMR_NB)
|| !strcasecmp(mime, MEDIA_MIMETYPE_AUDIO_AMR_WB)) {
ret = new AMRExtractor(source);
} else if (!strcasecmp(mime, MEDIA_MIMETYPE_AUDIO_FLAC)) {
ret = new FLACExtractor(source);
} else if (!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_WAV)) {
ret = new WAVExtractor(source);
} else if (!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_OGG)) {
ret = new OggExtractor(source);
} else if (!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_MATROSKA)) {
ret = new MatroskaExtractor(source);
} else if (!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_MPEG2TS)) {
ret = new MPEG2TSExtractor(source);
} else if (!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_WVM)) {
// Return now. WVExtractor should not have the DrmFlag set in the block below.
return new WVMExtractor(source);
} else if (!strcasecmp(mime, MEDIA_MIMETYPE_AUDIO_AAC_ADTS)) {
ret = new AACExtractor(source, meta);
} else if (!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_MPEG2PS)) {
ret = new MPEG2PSExtractor(source);
}
}
- 使用extractor对文件做A/V的分离(mVideoTrack/mAudioTrack)
status_t AwesomePlayer::setDataSource_l(const sp<MediaExtractor> &extractor)
{
for (size_t i = 0; i < extractor->countTracks(); ++i)
{
sp<MetaData> meta = extractor->getTrackMetaData(i);
CHECK(meta->findCString(kKeyMIMEType, &mime));
if (!haveVideo && !strncasecmp(mime, "video/", 6))
{
setVideoSource(extractor->getTrack(i));
haveVideo = true;
}
else if (!haveAudio && !strncasecmp(mime, "audio/", 6))
{
setAudioSource(extractor->getTrack(i));
haveAudio = true;
}
}
}
void AwesomePlayer::setVideoSource(sp<MediaSource> source)
{
mVideoTrack = source;
}
- 根据mVideoTrack中的编码类型來选择video decoder (mVideoSource)
status_t AwesomePlayer::initVideoDecoder()
{
mVideoSource = OMXCodec::Create(mClient.interface(),
mVideoTrack->getFormat(), false, mVideoTrack);}
- 将mVideoEvent放入mQueue中，开始解码播放，并交由mVideoRenderer來画出
status_t AwesomePlayer::play()
{
return play_l();
}
status_t AwesomePlayer::play_l()
{
postVideoEvent_l();
}
void AwesomePlayer::postVideoEvent_l(int64_t delayUs)
{
mQueue.postEventWithDelay(mVideoEvent, delayUs);
}
void AwesomePlayer::onVideoEvent()
{
mVideoSource->read(&mVideoBuffer, &options);
[CheckTimestamp] mVideoRenderer->render(mVideoBuffer); postVideoEvent_l();
}
