ATV2 audio? Confirm or correct me!

[chille]

I have searched and trying to get the audio support för ATV/iTunes/iOS straight. I have gathered this much, so I would be grateful if some expert could confirm or correct my conclusion...

ATV2: Plays AAC 2 ch no matter what. Plays AAC 5.1 but outputs this as 2ch through HDMI, but throughputs 5.1 through optical (but in general, most hifi receivers cannot process AAC 5.1?). Throughputs AC3 5.1 _only_ if optical cable is present (and ATV settings allow?), but cannot play files with only AC3 5.1 if no optical cable is plugged in.

iOS: Plays AAC 2ch and 5.1 but outputs only 2 ch. Cannot play files with only AC3 5.1

The reason I am trying to get this straight, is how to convert my iTunes video library with maximum device-support and minimum hassle/converting.

I have read that most hifi receivers don't know how to process AAC 5.1, but if that is NOT the case I guess it would be the best solution to have only an AAC 5.1 audio track since ATV2 can play it whether or not optical connection is present or not, and iOS devices seems to handle AAC 5.1 as well.

But if it what I had read is correct, that most receivers can't handle AAC 5.1, then I guess I have to include AC3 5.1 _and_ AAC 2ch for maximum usability?

 

[KevinC867]

I can't answer all your questions, but I can say that all my encodes are done as m4v's with both 2-channel AAC and 5.1 channel AC3 tracks and the 5.1 AC3 plays fine through HDMI with no optical cable connected. I'm not sure you can have a valid m4v file without the 2-channel AAC track.

I'm curious where your 5.1 AAC tracks are coming from. Transcoded from AC3/DTS tracks on movies?

 

[chille]

I'm not sure you can have a valid m4v file without the 2-channel AAC track.

You can. I have several movies/tv-episodes with just one AC3 5.1 or AAC 5.1 audio track. With just AAC 5.1 track my ATV2 can play the files without optical cable present, but with just a AC3 5.1 track and no optical cable plugged in I get an error message that it can't be played. With just one AC3 5.1 track in the file and plugged in to my receiver with optical cable it plays just fine.

If both AC3 5.1 and AAC 2 ch tracks is in the mp4/m4v-file everything works on ATV2 with/without optical, as well as iOS devices.

However, the reason why I'm exploring this is because I would like to be able to use ffmpeg.exe on my HP NAS (running Win Home Server) to convert my movies. I have found out that it is possible to convert MKV files (h264+AC3 or AAC) and just copy the audio and video file into a mp4 container using ffmpeg.exe. It takes just 10-15 seconds for a 1 gb tv episode on my NAS even though it has just a atom processor, because no conversion is needed -- only reading/writing. But since most movies in MKV tends to be AC3 5.1 audio, if I use this fast method I can't play the converted files on my ATV2 without optical cable present, or my iOS devices, because ATV2 and iOS devices cannot process AC3 on it's own. Converting audio tracks on my NAS takes forever since it has a crappy Atom processor.

I'm curious where your 5.1 AAC tracks are coming from. Transcoded from AC3/DTS tracks on movies?

Yup, I just found a couple of TV-shows I had converted some time ago where I had converted the AC3/DTS to AAC 5.1 for some reason. I most often have a AC3 5.1 and a AAC 2ch track so I can play the files on all devices.