Allow AC3 audio when transcoding to applehttp

[Dan]

Currently, the only audio choice for applehttp transcoding is aac. While aac support multi-channel audio, due to licensing issues all Roku media streamers convert multi-channel aac to two channel PCM. Since applehttp is the preferred method of transcoding for Roku players (allows fast forward and rewind capability), it is desirable to be able to retain multi-channel audio whenever possible.

Remember that it is possible that the audio codec being transcoded to have more than 5.1 audio. It is common for Dolby TrueHD or DTS Master Audio to contain 7.1 channels, and with Dolby Atmos/DTS:X encoding even more channels could exist. So support for a channel count higher than 5.1 is necessary.

[Petr Nejedly]

Looks like many audio codecs are supported: https://en.wikipedia.org/wiki/HTTP_Live_Streaming https://developer.apple.com/library/archive/documentation/NetworkingInternet/Conceptual/StreamingMediaGuide/FrequentlyAskedQuestions/FrequentlyAskedQuestions.html

Apple also allows h265 now: https://www.streamingmedia.com/Articles/Editorial/Featured-Articles/HEVC-in-HLS-10-Key-Questions-for-Streaming-Video-Developers-122637.aspx?CategoryID=429

[Dan]

This would be great to add H.265 and AC3 support. Roku still has the restriction of converting multi-channel AAC to two channel PCM, with the exception of the Roku Ultra 4640, which has a Dolby Digital encoder. So it will output the multi-channel AAC as Dolby Digital Plus.