なるほど、Nightlyに0.70.0-12が来たのか。

https://forum.doom9.org/showthread.php?p=1851429#post1851429

> LAV Filters 0.72.0-12 and newer have experimental support for AV1 decoding using libaom - software only, of course.
>　　https://files.1f0.de/lavf/nightly/
>
> It is planned to replace the libaom decoder with a ffmpeg built-in decoder once that becomes available, hopefully later this year.