Your primary concern is almost certainly power draw, so you're using a hardware encoder. The weight of a few more megabytes ROM would be inconsequential.
I mean the Ingenuity helicopter runs Linux, which seems to suggest that a few megabytes here and there isn't such a big deal; whatever the constraints of mars are, they seem to have a fair amount of onboard storage. I can't imagine that the improved video compression of AV1 compared to Theora or H.264 wouldn't outweigh the cost of that 4MB extra storage space.
That hardware selection was locked-in years ago, I think that's the major hold up with ginny in particular. I don't think even the next helicopter they're building now will be able to get hardware AV1 encoding. Would be moderately funny if they could eek better performance out of ffmpeg with remote updates.
