麻黄附子细辛汤荨麻疹:stagefright框架(三)- 选择Video Decoder
来源:百度文库 编辑:九乡新闻网 时间:2024/04/28 07:19:20
在《Stagefright (1) – Video Playback的流程》中,我们并没有详述Stagefright是如何根据影片档的类型来选择适合的video decoder,现在就让我们來看一看。
(1) Video decoder是在onPrepareAsyncEvent中的initVideoDecoder被決定的OMXCodec::Create()会回传video decoder给mVideoSource。
status_t AwesomePlayer::initVideoDecoder()
{
mVideoSource = OMXCodec::Create(mClient.interface(),
mVideoTrack->getFormat(),
false,
mVideoTrack);
}
sp
{
meta->findCString(kKeyMIMEType, &mime);
findMatchingCodecs(mime, ..., &matchingCodecs); ........ (2)
for (size_t i = 0; i < matchingCodecs.size(); ++i)
{
componentName = matchingCodecs[i].string();
softwareCodec =
InstantiateSoftwareCodec(componentName, ...); ..... (3)
if (softwareCodec != NULL) return softwareCodec;
err = omx->allocateNode(componentName, ..., &node); ... (4)
if (err == OK)
{
codec = new OMXCodec(..., componentName, ...); ...... (5)
return codec;
}
}
}
(2) 根据mVideoTrack的MIME从kDecoderInfo挑出合适的components
void OMXCodec::findMatchingCodecs(mime, ..., matchingCodecs)
{
for (int index = 0;; ++index)
{
componentName = GetCodec(
kDecoderInfo,
sizeof(kDecoderInfo)/sizeof(kDecoderInfo[0]),
mime,
index);
matchingCodecs->push(String8(componentName));
}
}
static const CodecInfo kDecoderInfo[] =
{
...
{ MEDIA_MIMETYPE_VIDEO_MPEG4, "OMX.qcom.video.decoder.mpeg4" },
{ MEDIA_MIMETYPE_VIDEO_MPEG4, "OMX.TI.Video.Decoder" },
{ MEDIA_MIMETYPE_VIDEO_MPEG4, "M4vH263Decoder" },
...
}
(3) 根据matchingCodecs中component的顺序,我们会先去检查其是否为software decoder
static sp
{
FactoryInfo kFactoryInfo[] =
{
...
FACTORY_REF(M4vH263Decoder)
...
};
for (i = 0; i < sizeof(kFactoryInfo)/sizeof(kFactoryInfo[0]); ++i)
{
if (!strcmp(name, kFactoryInfo[i].name))
return (*kFactoryInfo[i].CreateFunc)(source);
}
}
所有的software decoder都会被列在kFactoryInfo中,我们由传进来的name来对应适合的decoder。
(4) 如果该component不是software decoder,则试着去配置对应的OMX component
status_t OMX::allocateNode(name, ..., node)
{
mMaster->makeComponentInstance(
name,
&OMXNodeInstance::kCallbacks,
instance,
handle);
}
OMX_ERRORTYPE OMXMaster::makeComponentInstance(name, ...)
{
plugin->makeComponentInstance(name, ...);
}
OMX_ERRORTYPE OMXPVCodecsPlugin::makeComponentInstance(name, ...)
{
return OMX_MasterGetHandle(..., name, ...);
}
OMX_ERRORTYPE OMX_MasterGetHandle(...)
{
return OMX_GetHandle(...);
}
(5) 若该component为OMX deocder,则回传;否则继续检查下一个component