Which client? Works fine here

Hmmm what do you mean the video kept crashing? Where is your server set up? What are you using for OS? Is it bare metal, is it running in a Windows, in a VM, in a container?

In my case it's running in a Proxmox LXC container (the container is running Ubuntu). I'm passing through the integrated GPU, as instructed in the Jellyfin docs. And then I enable Intel QSV transcoding on Jellyfin. The CPU consumption is close to negligible. Then again, you need an Intel CPU capable of x264 transcoding at decent rates. Anything after 8th gen should be able to do the trick (with this I mean, you can ALSO transcode whatever source to x265 on the fly, but that's not a feature I'm actively using at the moment, as the resulting file is usually larger anyway). I'm using an i5 9500T, and I benchmarked something like 8 transcodes simultaneously to almost no impact. I think it was starting to be noticeable past 12 transcodes simultaneously. But that's some heavy streaming there! That'd mean EVERYONE is connecting at once to your server using FF (I believe Chrome is x265 capable, and the apps also take x265 just fine if your phone/computer support it). So...in short, my i5 from a few generations ago is already overkill for x265