There is a site Bountysource where you can contribute to a "bounty" towards resolving a bug/feature request. It's supported by the FFmpeg team and integrated with their issue tracker, so pages on Bountysource are already available for each issue.
Here's their entry for the AC-4 issue:
https://www.bountysource.com/issues/831 ... -4-support
Another open issue that affects ATSC 3.0 is the lack of support for interlaced HEVC that some stations are using, so these stations currently appear as 1920x540p instead of 1920x1080i in VLC:
https://www.bountysource.com/issues/655 ... -1920x540p