Android平台Stagefright中增加flv/f4v支援及相關原理介紹

Android平台Stagefright架構的文檔非常少，以下兩篇文章比較好，可以參考一下：

http://blogold.chinaunix.net/u1/57901/showart_2423206.html

http://blogold.chinaunix.net/u2/61880/showart_2339481.html

筆者最近在NV Tegra2的Android平台完成了stagefright中增加flv支援，基本能正常播所有本地和線上flv（h264+aac）檔案。細節還是非常多的，一不留神就可能在一個小細節上卡上好幾天。

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整個視頻播放的過程（我就懶得畫圖了）：
MediaPlayerService調用StagefrightPlayer
StagefrightPlayer調用AwesomePlayer
AwesomePlayer調用OMXCodec
OMXCodec調用Extractor中相關方法
OMXCodec調用Android標準的IOMX介面（即Stagefright中的OMX實現），OMX實現調用OMXMaster，OMXMaster調用OMXPluginBase外掛程式介面獲得外部codec的外掛程式
OMXCodec調用render模組實現渲染

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Google大牛教我們如何在Stagefright中增加FLAC的支援，其他音視頻格式同理（不過視頻比純音頻要難得多）：

There is no documentation on Stagefright. I haven't tried implementing a new stream type yet, but it does look pretty straightforward:

1. Create a FLAC stream extractor. See MP3Extractor.cpp or AMRExtractor.cpp for examples of audio stream extractors. It needs to be able to handle things like sniff a file to recognize FLAC content, seek in the stream, resync, etc. Add the new extractor to the list of stream extractors registered in DataSource.cpp.

2. Create a FLAC decoder node. See MP3Decoder.cpp or AMRNBDecoder.cpp for examples. Add the new codec to various places in OMXCodec.cpp so that the player engine can find it. Add the new mime type to the list of supported formats.

3. Add the FLAC container format to the MediaScanner (3 place if I remember correctly). This may already in Kenny's original FLAC submission.

4. Add FLAC to the unit tests in the media test framework.

This took all of about 5 minutes of spelunking in the code. The trick is just to use the existing audio formats as a guide.

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先在此打個樁，容我日後完善此篇部落格。