[Libav-user] Slow down video

[Sushma]

Thanks for the reply.

If pix_fmt=0 does not work, what are the other pixel formats that I can use
to achieve my requirement?

>>atrim gets from [in1], i.e. buffer, while in the other version atrim is
connected to [0:a], i.e. a abuffer.

Do you think I need to use it in a similar way in the API as well? If
possible, can you share a sample filter string that I could use? I tried
all possible ways but with no luck.

Regards,
Madhukar

On Fri, Oct 14, 2022 at 6:43 PM Nicolas George <george at nsup.org> wrote:

> Sushma (12022-10-14):
> > Hello All,
> >
> > I'm trying to use FFMPEG to slow down part of video and audio using C++
> > FFMPEG API. I was able to achieve it from the command line but however,
> > argument parsing fails using api.
> >
> > Here is the command line input
> >
> > ffmpeg -i "inputvideo.mp4" -filter_complex
> >
> "[0:v]trim=0:2,setpts=PTS-STARTPTS[v1];[0:v]trim=2:10,setpts=2*(PTS-STARTPTS)[v2];[0:v]trim=10,setpts=PTS-STARTPTS[v3];[0:a]atrim=0:2,asetpts=PTS-STARTPTS[a1];[0:a]atrim=2:10,asetpts=PTS-STARTPTS,atempo=0.5[a2];[0:a]atrim=10,asetpts=PTS-STARTPTS[a3];[v1][a1][v2][a2][v3][a3]concat=n=3:v=1:a=1"
> > -preset superfast -profile:v baseline output.mp4
> >
> > Here is the filter string i used in avfilter_graph_parse()
> >
> >
> buffer=video_size=1920x1080:pix_fmt=0:time_base=1/30:pixel_aspect=0/1:frame_rate=30/1
> > [in_1]; [in_1] trim = 0:2, setpts = PTS - STARTPTS [in_2]; [in_2] trim =
> > 2:10, setpts = 2 * (PTS - STARTPTS)[in_3]; [in_3] trim = 10, setpts =
> PTS -
> > STARTPTS[in_4]; [in_1] atrim = 0:2, asetpts = PTS - STARTPTS[in_5];
> [in_5]
> > atrim = 2:10, asetpts = PTS - STARTPTS, atempo = 0.5[in_6]; [in_6] atrim
> =
> > 10, asetpts = PTS - STARTPTS[in_7]; [in_1] [in_2] [in_5] [in_3] [in_6]
> > [in_4] [in_7] concat = n = 3:v = 1 : a = 1 [result]; [result] buffersink
> >
> > Can anyone let me know where I'm wrong? What changes do I need to make in
> > the filter string? Kindly help
>
> I see several issues:
>
> pix_fmt=0 will probably not work.
>
> atrim gets from [in1], i.e. buffer, while in the other version atrim is
> connected to [0:a], i.e. a abuffer.
>
> You have several pads that are connected multiple times.
>
> Regards,
>
> --
>   Nicolas George
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