Auto postprocess videos and thumbnail

[ahuang11]

The script:

• trims the video by 1 second
• converts webm to mp4
• moves the videos into the assets directory
• move the thumbnails to the assets directory

[codecov-commenter]

Codecov Report

All modified lines are covered by tests :white_check_mark:

Comparison is base (ebaf4b1) 98.41% compared to head (b3e0e62) 98.41%. Report is 4 commits behind head on main.

:exclamation: Current head b3e0e62 differs from pull request most recent head b9271f9. Consider uploading reports for the commit b9271f9 to get more accurate results

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #64 +/- ## ======================================= Coverage 98.41% 98.41% ======================================= Files 2 2 Lines 63 63 ======================================= Hits 62 62 Misses 1 1 ```

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[MarcSkovMadsen]

Really Nice script

Something to think about is whether the .mp4 files should be a part of this repository, be hosted on an external CDN or be autogenerated when the docs build?

[ahuang11]

I think the mp4 can stay in this repo; this repo is just for examples anyways.

Autogenerated when the docs build may take too long I suspect.