[Ffmpeg-devel] Trouble with av_seek_frame() and av_read_frame()

[Devin Lane]

ffmpeg-devel:

I'm having some trouble using av_seek_frame(). I want to use it to  
seek both forwards and backwards, both by frame and keyframe.

Right now, my strategy is to seek to a position ahead of my current  
one, flush the codec buffers, then read the next frame using  
av_read_frame(). I can't say I'm having much luck in getting that to  
work.

Here's where my confusion lies:

1. I'm getting the current timestamp from the last displayed packet's  
pts value. I figure if I add, say, 10 to that and seek to that  
position I should get to the next keyframe, but it appears to go to  
just the next frame. I'm using the following call:
	av_seek_frame(formatContext, -1, (cur_pts+10), 0);

What am I doing wrong? I suspect it has a lot to do with the  
timestamp units -- I can't seem to figure out which units they should  
be in. I don't understand what units the packet's pts value is in, so  
I don't know how to convert it to something acceptable for  
av_seek_frame()

2. I can't seem to seek backward in the video at all. Even when I  
seek to a timestamp of 0, I end up going forward.

3. I can't find a way to get the total number of frames in the movie.  
I call formatContext->streams[videoStream]->nb_frames; but get a  
value of 0.

Thank you very much,
Devin Lane