High CPU Usage

[TheDreadPirate]

Code:

-codec:v:0 libx264

You're trancoding. And on the CPU. Not that the Rpi5 has a hardware encoder.

Your choices are to turn off transcoding and deal with the breakage that will result when clients can't play videos or pre-transcode on another machine to a more compatible format.

H264 main 8-bit
AAC stereo
burned in subtitles or external SRT subtitles
MP4 container.