At least with AMD GPU, an easy way to do it is to check usage of VCN. Something like this (assuming your GPU index is 0): watch -n 1 sudo cat /sys/kernel/

At least with AMD GPU, an easy way to do it is to check usage of VCN. Something like this (assuming your GPU index is 0): watch -n 1 sudo cat /sys/kernel/debug/dri/0/amdgpu_pm_info You should see there: VCN: Enabled If GPU accelerated video is being played. I think you might need to set this flag to true in Firefox's about:config (or it might be not needed anymore): media.ffmpeg.vaapi.enabled