Handbrake uses FFmpeg under the hood, so if you like a GUI that's probably the best option. For using FFmpeg directly, any LLM should be able to do a good job of devising the correct command line to do whatever you want. For Nostr I use h264 for the video codec for widest compatibility.
Discussion
Thanks, anything else I should know about nitrate resolution, etc?
I usually drop the resolution for social media posting personally, 480 or 720 is fine. For the bitrate look into the crf (Constant Rate Factor) option. The higher you set this the lower the bitrate. Depending on the video it can save a lot of space without losing too much quality.
`-c:v libx264 -crf 22 -preset slow` is a good baseline and adjust from there.
A pretty in depth article covering FFmpeg.