SOLVED: Server crash when transcoding high resolution

[TheDreadPirate]

I'm also getting this same behavior.

Was on 10.10.5: twice my friend tried streaming a 4K file via the browser that triggered transcoding, and my proxmox server crashed / shutoff immediately after.

Haven't been able to see anything in logs that would indicate a crash/error of some sort.

How much free space do you have on the disk that Jellyfin runs off of?  Transcodes/remuxes are written to disk and transcodes of 4K files can consume as much, and often more, than the original file.  So, for example, an 80GB 4K HDR file will consume 100+GB of disk space for the transcode.

You can try enabling "Delete segments" and "Throttle transcodes" in Dashboard > Playback > Transcoding to reduce the disk space usage from transcodes/remuxes. Assuming that is the problem you are having.