Config: Add option to stream videos over the specified CDN

[shivanshs9]

Describe what problem this solves and why this would be valuable to many users

Right now, the PHOTOPRISM_CDN_URL envvar only enables static assets, thumbnails and compressed library images to be delivered via CDN. Not for video files.

Describe the solution you'd like

CDN could be enabled for videos too.

[lastzero]

Videos are complicated in that these are streamed, the supported formats must be detected and the video must be transcoded on demand if the format is not supported or the bitrate is too high. We found this not to work well with (at least) our provider and that's why it's not supported. If you have a lot of practical experience and know how to build it so that it always works and is compatible with any CDN provider, please let us know! 👍

[lastzero]

@shivanshs9 This issue is related to what I've been working on this week:

• Config: Add advanced HTTP cache control options #3297

If I remember correctly, KeyCDN had problems with video streaming. I can't remember any details though. It will definitely cause a lot of extra traffic that you have to pay for. Not all users might want to do that!?

Cloudflare doesn't support video by default either, only for an additional fee (because of the traffic it causes).

Note that we had to switch our website and demo.photoprism.app from KeyCDN to Bunny CDN last weekend, which might work better for videos based on the settings I've seen in their admin UI.

I've also started working on a CDN setup guide (contributions and feedback welcome):

• https://docs.photoprism.app/getting-started/using-a-cdn/

[lastzero]

An updated preview build will be available for testing soon. As always, help with testing is much appreciated! Thank you ❤️