[Libav-user] MPEG4 decoding - in reverse order

amol mahamuni ajm2707 at yahoo.com
Mon Sep 12 08:12:10 CEST 2011

Hello Experts!

I have MPEG4 stream from rtsp server. I could decode it and play it using ffmepg library.

I stored the stream as binary files for later playing using ffmpeg library. 
I can play the stream in forward direction - just I want to feed the ffmpeg decoder with stored frames.

A)Now, my requirement is to play the stream in reverse direction. Can you ppl suggest me a way to accomplish this?
I tried to feed the stored packets/data in reverse way but of course it's giving  bad stream (distorted and ill-motion video display).
Is there any trick through which decoder can understand about reverse playing? Is reverse playing possible with ffmpeg decode?

B)Also, what is key frame in MPEG4 video stream? How can I understand key frame?
If I could understand key frame, does decoder give a good decoded frame when I fed it with key frame?

My understanding is that when I feed MPEG4 key frame, ffmepg will output good decoded frame
- meaning key frame does not depend on other frames to produce good decoded frame output. Is it correct?

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