AAC renders as 3 channel from a DTS 5.1 MKV source, why?

[eug7]

I have an MKV avc and 6 channel DTS. When setting video source to copy and audio to AAC as a mux to mp4 the result file is not 6 channel or 5.1. I find that converting to mp4 allows the file to import to the Sony Vegas timeline. Media info confirms 6 channel and if I use eac3to to convert the DTS to ac3 and use tsmuxer to mux to m2ts I see the result in Vegas as 6 channel but Vegas is finicky about m2 ts. Vegas likes avc AAC mp4 the best. What am I doing wrong?

[Jan Gruuthuse]

If you are using avidemux 2.6? Check settings in Main Menu -> Audio -> Select Track.
And see what tracks are available and options for these track(s)? Could be problematic: as DTS is a proprietary audio codec?

Provisional Warning: DTS Inc. claims that use of libdca software, to decode DTS compressed sound data on a DVD could violate DTS's patent rights. If you are unsure about the legality of using and distributing this code in your country, in particular in the USA, please consult your lawyer before downloading it.

[eug7]

Using tmpgenc mastering works 5 I can encode the audio to AAC 5.1. Using avidemux 2.5 I can keep the video quality (copy) use the tmpgenc audio and mux both to mp4. If I use 2.5 or 2.6 to convert the audio I get dud results as stated in my original post. Also, I didn't notice when I wrote my first post but the file I was trying to mux to mp4 in 2.6 was out of audio sync. Avidemux has problems.

[Jan Gruuthuse]

Going with video from avidemux 2.5 to avidemux 2.6 could cause issues. The 1st is frame based, the second is time based.
transcoding 5.1 from 1 audio codec to another causes another problem to. The audio matrix is not the same (FR,C,FL,SR,SL & LFE) so channels are switched of position.