.MKV Audio can only be split into 2 channels once extracted (I want 6)

[54321blastoff]

I am trying to extract the audio from a .mkv file and split the audio into 6 channels (more specifically get the Center channel) but the last 4 files I tried it on, I keep only getting 2 audio channels and I can't understand why.

I download a 720p HDTV .x264-Dimension .mkv file.
I use MKVExtractGUI to extract the Audio (A_AC3) track
I now have the .ac3 audio file on my computer
I open AC3Tools Pro and click Demux AC3 and easily split the Audio BUT where it says Step 2: Select Demuxed Channels, only the Right and Left Front Channels have boxes I can check, the other channels including the Center channel which is what I am really after is faded and can not be extracted because the Audio file is only made up of 2 channels.

Why is this happening? I know I am doing the steps correctly so why is the audio track being extracted with MKVExtractGUI from the .mkv file only have the potential to be split into 2 channels? I did it last week once and it worked fine with all the channels as an option in AC3 Tools Pro so I could easily get the Center channel but since then every time I extract the .ac3 audio track from a different .mkv file and open it in AC3Tools, only 2 channels can be extracted. I have also tried using eac3to and again, it can only be split into Left and Right channels, not the 6 I want (or really the center). Huh?

[poisondeathray]

are you sure it's 5.1 audio? what does mediainfo say ?

what commandline did you use for eac3to ?

if you open in audacity (or any audio editor), can you see 6 channels ? if so , delete all the channels except the center and export it

[54321blastoff]

I tried opening the .ac3 file in Audacity and still just 2 channels. I tried putting in the .ac3 file from last week that I was able to then split into 6 in AC3Tools Pro and yup, Audacity split it into 6 channels too so I guess the file I'm trying to get the center channel from is only 2 channels to start with.

I don't know much about this stuff (learned the process in my OP from research) but I thought the audio file in .mkv was automatically 6 channel audio and not 2. Hmm...yet 5 of the last 6 .mkv files I downloaded, the .ac3 audio tracks I extracted were just 2 channels & could not be split further.

[johns0]

720p HDTV .x264-Dimension .mkv are current running tv shows where the audio can be 2.0 or 5.1 ac3 so most likely the audio you extracted is 2.0 ac3.

My store bought supernatural season 1 dvds have 192kbs 2.0 ac3 for audio.