[Libav-user] Slow down video

bsenftner at earthlink.net bsenftner at earthlink.net
Sat Oct 15 17:36:34 EEST 2022

I have an ffmpeg video player that has the same AVFilter Graph text string inputs as the command line ffmpeg. You could try looking at how I setup the code and compare with what you’re doing.


The key bits are in this file:



There’s a frame manager class implementing frame filters starting around line 110. 


Note, this does not do audio, but I’ve been told by a dev with a similar playback library the audio handling is very similar. 


From: Libav-user <libav-user-bounces at ffmpeg.org> On Behalf Of Sushma
Sent: Saturday, October 15, 2022 7:36 AM
To: This list is about using libavcodec, libavformat, libavutil, libavdevice and libavfilter. <libav-user at ffmpeg.org>
Subject: Re: [Libav-user] Slow down video


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.





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


  Nicolas George
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