AV1 codec support (dav1d, aom, svt-av1) in VLC and FFMpeg

[nagmat84]

I am wondering what use flags I need to enable to get support for AV1 decoding.

This a list of packages, AV1-related use flags and their default setting:

• media-video/vlc
  • aom (disabled)
    
  • dav1d (disabled)
• media-video/ffmpeg
  • dav1d (enabled)
    
  • libaom (disabled)
    
  • svt-av1 (disabled)

Moreover, media-video/vlc supports the use flag ffmpeg, which is enabled by default.

Does this mean that VLC is able to decode AV1 video indirectly via ffmpeg?

What would change, if dav1d is also enabled for media-video/vlc directly? Are there any advantages or disadvantages in terms of efficiency, quality or stability?

What are the advantages/disadvantages of the other AV1-libraries? What library is used if support for more than one is enabled?