Old version ffmpeg read stream detection format from memory and decode

New and old version ffmpeg different ways to decode the video stream from memory for unknown format.

The new version (using Avcodec_decode_video2, etc. ) will not be said first, relatively simple.

For older versions, it is more cumbersome. Refer to the following:

Http://www.acnenomor.com/3857007p1/process-video-stream-from-memory-buffer

Http://fossies.org/linux/mythtv/mythplugins/mytharchive/mytharchive/remoteavformatcontext.h

https://cdry.wordpress.com/2009/09/09/using-custom-io-callbacks-with-ffmpeg/

Old version ffmpeg read stream detection format from memory and decode