https://github.com/matrix-org/matrix-spec-proposals/pull/4034

For https://github.com/turt2live/matrix-media-repo/issues/413
For https://github.com/turt2live/matrix-media-repo/issues/412

For https://github.com/turt2live/matrix-media-repo/issues/407
For https://github.com/turt2live/matrix-media-repo/issues/408
For https://github.com/turt2live/matrix-media-repo/issues/409

Fixes https://github.com/turt2live/matrix-media-repo/issues/73

Fixes https://github.com/turt2live/matrix-media-repo/issues/349

This reverts commit 5e51abbd.

For https://github.com/turt2live/matrix-media-repo/issues/53

Fixes https://github.com/turt2live/matrix-media-repo/issues/323

See https://github.com/turt2live/matrix-media-repo/security/advisories/GHSA-j889-h476-hh9h

Fixes https://github.com/turt2live/matrix-media-repo/issues/312

This needs to be expanded to cover more of what ffmpeg covers. This does not support animation for a few reasons:
* Most clients which will be using a video thumbnail will be using it in such a way where even a GIF isn't supported.
* Clients rely on the thumbnail endpoint returning images, which can lead to resource inefficiencies if we return GIFs.
* Returning more optimized thumbnails is not feasible for compatibility with most clients.

This is a step towards video processing, maybe.

Fixes https://github.com/turt2live/matrix-media-repo/issues/100

Fixes https://github.com/turt2live/matrix-media-repo/issues/146

Fixes https://github.com/turt2live/matrix-media-repo/issues/49

For https://github.com/turt2live/matrix-media-repo/issues/15

Fixes https://github.com/turt2live/matrix-media-repo/issues/188