There is not much, unless you're working with AV1. rav1d is the alternative there but you've got to trade off some performance for security gains.

ffmpeg is a monopoly in the space which means that you either take the exact set of tradeoffs they offer, or... well, you have no alternatives, so take it.

Of course the alternatives are never going to be as good as the originals until they've had more effort put into them. It took _years_ until the Rust gzip/zip libraries surpassed the C ones while being more secure overall.