[FFmpeg-user] hstack with one video offset in time?

[Paul B Mahol]

On Fri, Mar 5, 2021 at 10:54 PM Peter White <peter.white at posteo.net> wrote:

> On Fri, Mar 05, 2021 at 11:33:10AM -0800, Steven Kan wrote:
> >
> > >>>
> > >>> I’d like to assemble these videos, side-by-side, but synced in time,
> which
> > >>> means the TrailDown video needs to start 50 seconds after the TrailUp
> > >>> video. The TrailDown side can be black/blank, or it can be stuck on
> the
> > >>> first frame of its video while the right side plays for the first 50
> > >>> seconds; it doesn’t matter to me.
> > >>>
> > >>> I’ve tried all of the following:
> > >>>
> > >>> -itsoffset 50 -i TrailDown.mp4 -i TrailUp.mp4
> > >>> -itsoffset 50 -i TrailDown.mp4 -itsoffset 0 -i TrailUp.mp4
> > >>> -i TrailDown.mp4 -itsoffset -50 -i TrailUp.mp4
> > >>>
> > >>
> > >> see tpad filter, need recent version.
> > >
> > > Thanks! I have figured out the syntax to pad a single video with tpad,
> e.g.:
> > >
> > > ffmpeg -i
> /Users/steven/Downloads/Record/DownLoad/TrailDown_ch1_20210304010952_20210304011838.mp4
> -filter_complex "tpad=start_duration=50" tPadOut.mp4
> > >
> > > but I’m having trouble with the syntax to delay only one of two videos
> in an hstack filter:
> > >
> > > ffmpeg -i
> /Users/steven/Downloads/Record/DownLoad/TrailDown_ch1_20210304010952_20210304011838.mp4
> -i
> /Users/steven/Downloads/Record/DownLoad/TrailUp_ch1_20210304010838_20210304011506.mp4
> -filter_complex "tpad=start_duration=50[v0];hstack=inputs=2” Coyote2Up.mp4
> >
> >
> > I brute-forced it by using tpad to pad the first video by itself, and
> then I used hstack to glue them together. Not the most efficient way of
> doing things, and I think that induces 2 generations of transcoding, so
> ideally I’d like to know how to do it properly in the future. But here’s
> the end result:
>
> You need to map your input files to the appropriate filter pads in a
> complex graph. Since I use this kind of filter graph very rarely, I
> cannot tell you offhand how to do this properly. The manual section on
> this should be a good start though.
>
> Of course, you can always try the approach I suggested in the other
> subthread. No transcoding of the original there until you get to the
> last stage.
>

Your approach is very very bad.

>
>
> Peter
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