Cache transcoded live photo videos

[pulsejet]

HEVC live photos get transcoded every time they're opened. This is slow especially on CPU.

#234

[bnw]

First of all, thanks a lot for your awesome project ❤

Sharing some thoughts on this ticket:

Adding caching for the transcoded live features would mean a big improvement for my setup: A raspi4 with lots of storage but slow CPU, which needs around 10s to transcode the live video.

A potential alternative could be to directly stream the video data that is contained in the image file to the browser, if the browser supports it, and skip the transcoding. For >90% of devices, this could work, avoiding the downsides & complexities of caching.
I'm not sure how difficult it is to extract the video data & wrap it in some container format without transcoding it.