support for AV1 codec?

[Selur]

Since you did not care to share details and only wrote:

Any preview not working.

I spend an hour testing different av1 files with in different containers and so far from the looks of it only Avisynth ffmpegsource has problems with av1 when it's inside an mp4 container.
Could not reproduce any other problem.
-> When using Avisynth: Use LibavVideoSource instead of FFmpegSource.

Cu Selur