I have a working program built on top of [libav](http://libav.org/) (alternatively [ffmpeg](http://ffmpeg.org/) - expertise is either is useful here).

It takes an mp4 video, encoded with h264 video / AAC audio, and remuxes it to MPEG TS and segments it into X second chunks. It is analogous to the following ffmpeg command:

```
ffmpeg -y -i video.mp4 -c:a copy -bsf:a aac_adtstoasc -c:v copy -bsf:v h264_mp4toannexb -flags -global_header -map 0 -f segment -segment_time 10 -segment_list playlist.m3u8 -segment_format mpegts chunk_%03d.ts

```

The reason I am not using the command-line, is that I wish to generate only a subset of the segments. So if a video results in 10 segments of between 8 and 12 seconds (the segments are never exactly the desired length due to keyframes), I might wish to generate segments 3-7 at a later time.

The complete code for my program can be found [here](http://pastebin.com/qj3hzDDn).

I use `av_read_frame` to read every frame from the source file, remux (including a bitfilter process) and write to output file. Once the duration since the last output becomes close/greater than the desired segment length, I flush the output file, close it, open the next segment and continue.

I have tried altering the code to do an `av_seek_frame` to the end of the first segment and start from there (I also attempted to start at the end of the 2nd and 3rd segment). The new segments are the same length (in seconds and pts), but have a different size than the comparable segments from the full runthrough (within a few kilobytes) - the starting segment (whether it's the 2nd, 3rd or other) also shows as having 2 packets LESS than the comparable segment from previously.

I assumed that `av_seek_frame` would give me an exact match as if I had manually done a loop with `av_read_frame` up to that frame, but it seems like it's not the case.

What I wish for:

* A way to "fast-forward" in the file to a specific (**not** approximate) point in the file.
* To write from that point forward and have the output be completely identical to the output a full run provides (same size, same length, same exact bytes).