[Libav-user] rewind file

[Slash]

Thanks. I have tried it just now but unfortunately it won't enter the
second while loop (so it doesn't seem to decode anything for the 2nd time..)

Now I have also tried avformat_seek_file(pFormatCtx, -1, 0, 0, 0,
AVSEEK_FLAG_BACKWARD); (correct usage?) and it makes no difference.

Is it maybe the case that once the whole file is decoded, you cannot go
back?


On 18 June 2014 15:04, Info || Non-Lethal Applications <
info at non-lethal-applications.com> wrote:

> I’d say av_seek_frame (or avformat_seek_file) is what you’re after.
>
> av_seek_frame(pFormatContext, -1, 0, AVSEEK_FLAG_BACKWARD);
>
> Best,
>
> Flo
>
> On 18 Jun 2014, at 14:54, Slash <slashpm at gmail.com> wrote:
>
> Hello,
>
> I'm developing a crypto-related application using h264 streams (only
> video). I'd like to decode the frames multiple times after changing some
> info in them (dct, mv, whatever), so the decoded result is always different
> a little bit but I always want to deal with same input file.
>
> I followed the tutorial here (tutorial01.c):
> https://github.com/chelyaev/ffmpeg-tutorial
>
> so the decoding code in question looks like this:
>
> while (av_read_frame(pFormatCtx, &packet) >= 0) {
> // Is this a packet from the video stream?
>  if (packet.stream_index == videoStream) {
> // Decode video frame
> avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet);
>  }
> }
> // Free the packet that was allocated by av_read_frame
>  av_free_packet(&packet);
> }
>
> After this while loop, all the frames are decoded. What I want is to
> change something and then redo the previous while loop to decode the frames
> again. How can I start it all over again?
>
> I have tried using av_seek_frame(pFormatCtx, videoStream, 0,
> AVSEEK_FLAG_ANY) to jump back to the beginning but apparently I didn't get
> any new decoded data so it is not doing what I need.
>
> Thanks for help.
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>
>
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