Problem with DTS-HD Mater/5.1

[johnr283]

I have an MP4 with DTS-HD Mater/5.1 audio. However, Avidemux shows the audio track as Unknown codec, 6 chan. I need to edit the video using keyframes and save as Copy. When I try to save with Audio Output: copy, I get an error message. Unsupported Audio track 1 out of 1 is incompatible Only AAC, AC3, DTS, E-AC3, MP2, MP3 and Vorbis supported for audio. If I change the output to AAC, the video won't play correctly. If I change it to AC3, Avidemux freezes and won't respond.