According to MPEG-LA, MPEG-2 is patent free in the United States now.

This task first needs to answer, in which file format it wants to support the codec. Codec detection happens in the file format parsing, so for each file format you want the codec to be supported in, you will have to take separate technical steps on that level (and thus likely separate tickets).

Question: should other profiles of AAC be enabled or just AAC-LC?

Current state of this:

• AAC-LC is "probably ok" but we'd need to run through legal first
• avoid touching any other variants for now :D
  • therefore if accepting *input* we must check what things actually use? or do we care? or check legal?
• upload input with AAC is not uncommon in MPEG-2 and *very* common in MP4/ISO-BMFF flavor formats (.mp4, .m4a, .mov, .3gp)
  • the upstream getid3 library we use for metadata has a bunch of bugs in the MPEG parser and doesn't grok AAC or AC3 tracks, needs fixing
  • not sure if we can detect AAC-LC vs AAC-HC with that on MP4s, need to double-check the spec
• transcode output of AAC-LC in fragmented MP4 for HLS-style streaming would be trivial to add, and would integrate nicely for HLS playback that I'm presently soft-launching for iOS but we will use on other OSs later via video.js+MSE.
• note that our other audio output formats for HLS tracks are currently limited to stereo (MP3 only does stereo, and Opus supports more channels but Apple's implementation is hardcoded to support stereo only!) so AAC output may be a requirement for multichannel surround sound output

Part of the reason why I waited was to aim for something like HE-AAC.