Yes, you can do that. There is no "user" mailing list because MLT is for
developers. You should use a GUI video editor that uses MLT to explore the
feasibility and mock it up. From there, one way forward is save or export
the MLT XML from one of these tools, figure a way to generate it, and use
melt to process the XML Another way is to learn how to generate the
equivalent command line.
On Tue, Jan 10, 2017 at 11:59 AM Alex Speller <a...@alexspeller.com> wrote:
> Apologies if this is the wrong mailing list, I only saw a devel list not
> a user list.
>
> I have a question about video compositing. I originally asked in the
> ffmpeg-user mailinglist and it was suggested that MLT/melt would be a
> better tool. So my question becomes, for the below outcome will it be
> feasible to achieve this and is it a good fit for my use case? I'm happy to
> dive into the docs but I don't want to go on a wild goose chase if I'm
> looking at the wrong tool for the job.
>
> I’ve included the text of the question below but I’ve also put it in a
> gist for easier to read formatting here:
> https://gist.github.com/alexspeller/aefdd5a6d7100d28d0bbc4838527f797
>
> I have multiple mp4 video files and I want to composite them into a single
> video on the command line. Each stream is an mp4 video. They are of different
> lengths, and each file also has audio.
>
> The tricky thing is, I want the layout to change depending on how many
> streams are currently visible.
>
> As a concrete example, say I have 3 video files:
>
> | File | Duration | Start | End |
> |-------|----------|-------|-----|
> | a.mp4 | 30s | 0s | 30s |
> | b.mp4 | 10s | 10s | 20s |
> | c.mp4 | 15s | 15s | 30s |
>
>
> So at t=0 seconds, I want the video to look like this:
>
> ```
> +-------------------------+
> | |
> | |
> | |
> | |
> | a.mp4 |
> | |
> | |
> | |
> | |
> | |
> +-------------------------+
>
>
> ```
>
> At t=10s, I want the video to look like this:
>
> ```
> +------------------------------+--------+
> | | |
> | | |
> | | a.mp4 |
> | | |
> | +--------+
> | b.mp4 |
> | |
> | |
> | |
> | |
> | |
> +------------------------------+
> ```
>
> At t=15s, I want the video to look like this:
>
> ```
> +------------------------------+--------+
> | | |
> | | |
> | | a.mp4 |
> | | |
> | +--------+
> | b.mp4 | |
> | | |
> | | c.mp4 |
> | | |
> | +--------+
> | |
> +------------------------------+
> ```
>
> And at t=20s until the end, I want the video to look like this:
>
> ```
> +------------------------------+--------+
> | | |
> | | |
> | | a.mp4 |
> | | |
> | +--------+
> | c.mp4 |
> | |
> | |
> | |
> | |
> | |
> +------------------------------+
> ```
>
> Ideally there would be some animated transitions between the states, but
> that's not essential.
>
> I have found two possible approaches that might work, but I'm not sure what
> the best one is. The first is using
> [filters](https://trac.ffmpeg.org/wiki/Create%20a%20mosaic%20out%20of%20several%20input%20videos)
> to acheive the result, but I'm not sure if it will cope well with (a) the
> changing layouts and (b) keeping the audio without any artefacts when the
> layout changes.
>
> The other approach I thought of would be exporting all frames to images,
> building new frames with imagemagick, and then layering the new frames on top
> of the audio like in [this blog
> post](https://broadcasterproject.wordpress.com/2010/05/18/how-to-layerremix-videos-with-free-command-line-tools/).
>
> Any suggestions on if either of these approaches is better, or any
> alternatives? Thanks!
>
>
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