no file extensions for audiobooks

[TomW1605]

despite having audio quality profiles there are no file extensions listed for audio files in MediaFileExtensions.cs

[ta264]

There's a lot of work to do to support audiobooks. I plan to sort regular books first so don't expect progress for a while

[TomW1605]

that's fine i just figured it might as well be documented

[madknave]

I know this is down the line and low priority at the moment, but is there a plan for audiobooks with multiple files (i.e. separated chapters)? I'm all about merging these type of abooks (and maybe standardizing to an m4b file type).

Just wanted to leave a floating thought for when you start working on developing this part.