Comment by Gormo

> I wonder why ffmpeg doesn't just auto detect this?

Hardware encoding is often less configurable and involves greater trade-offs than using sophisticated software codecs, and don't produce exactly equivalent results even with equivalent parameters. On top of that, systems often have multiple hardware APIs to choose from that often different features.

FFMpeg is a complex command-line tool intended for users who are willing to learn its intricacies, so I'm not sure it makes sense for it to set defaults based on assumptions.