FFMPEG下如何从input buffer中读取bitstream？

There is an example in FFMPEG source code. bm_ffmpeg/doc/examples/avio_reading.c
This case makes libavformat demuxer access media content through a custom AVIOContext read callback instread of file, rtsp, etc protocols defined in FFMPEG.
This is an example in middleware-soc about using avio + jpeg_bm to decode still jpeg picture. (bm_ffmpeg/doc/examples/avio_decode_jpeg.c)