Convert slides/storyboards to video

[flanter21]

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Checklist

• [X] I'm requesting a feature unrelated to a specific site
• [X] I've looked through the README
• [X] I've verified that I have updated yt-dlp to nightly or master (update instructions)
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Provide a description that is worded well enough to be understood

Sometimes the slides may be higher quality than the video itself. Ideally, this could be combined with the audio from the video. However, the current mhtml implementation of slides does not allow this.

I envision that the slides could be shown sequentially, each running from the timestamp it appears until the next slide appears. Essentially this would be creating a video from the slides.

This would be useful for lectures as mediasite often saves video in very poor quality, but often takes high quality screenshots of the lecture and displays them instead of the video.

However, I do recognise that currently mediasite slide extraction is broken (per https://github.com/yt-dlp/yt-dlp/issues/10320) so instead YouTube could be used as a place to start as the current mhtml "storyboards" calculate the start and end time of each storyboard and the duration of each, so these values could be used to stitch them together.

Provide verbose output that clearly demonstrates the problem

• [ ] Run your yt-dlp command with -vU flag added (yt-dlp -vU <your command line>)
• [ ] If using API, add 'verbose': True to YoutubeDL params instead
• [ ] Copy the WHOLE output (starting with [debug] Command-line config) and insert it below

Complete Verbose Output

No response

[bashonly]

There was some discussion of this here: https://github.com/yt-dlp/yt-dlp/pull/343#issuecomment-860205931

but it was ultimately deemed too much of a hassle to do at the time, and mhtml was what was settled upon. Mediasite seems like a better candidate for video slides than Youtube, since they use a DASH/DASH-like manifest for them (or least they used to before the extractor broke).