[FFmpeg-user] Decoding frames as fast as possible

[Roger Pack]

Does ffprobe take 20s?

On Tue, Jul 3, 2018 at 2:23 AM, Evan <cerebro.alexiel at gmail.com> wrote:
> Hi everyone,
>
> I'm developping a media player featuring advanced video/frame processing.
> To be able to seek to any particular frame, I need to know, for each frame,
> its presentation time and if available, if it's a key frame or not. The
> latter is optional, really.
>
> To do that I build an "index" once the media is valid and opened.
> It's a basically a loop, fetching a packet, checking if it's the video
> stream I'm interested in, feeding the codec until he can produces a frame
> or reaching the end of the file.
>
> This is perfectly working but it's way too long for me, like 20 seconds for
> a ~800MB mp4/h264 file.
> I'm considering the following options:
> - building the index in the background while playing the media: I guess
> I'll have to copy the decoder context to not mix both processes but I
> expect having playback (stuttering) issues.
> - use multiple threads: from what I read, I can only use one thread for a
> stream. I may eventually use two threads, one for video and one for audio
> but I want to speed up video decoding fisrt.
> - use the GPU to decode frames faster: while it sounds like a good idea, I
> have to add two constraints: I'm on Windows 7 (and soon, Windows 10) and I
> want a generic approach so not H.264-only.
> - decode only packets: it's tempting but I think I will either loose
> timestamp information or precision (because of I, P, B frames.
> - use an option (av_dict_set) to do a dummy frame decoding: is there
> anything like that?
> - use reference counting to avoid costly frame allocations: I already tried
> that but didn't see any difference.
>
> For now, I will measure time elapsed in each piece of code in order to
> pinpoint lengthy operations.
> If you guys have any hint, I'd be glad to hear them.
>
> Thanks.
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