MKVToolNix eats up Dolby Atmos sound?

[MalickT]

Hi. I have TRUE-HD 7.1 Dolby Atmos sound file about 4.1 GB and video file 15GB. When I mux video & sound together using MKVToolNix. The final file size will be 18GB. Later when I demux only audio from the file. Its only 3GB. Where did the 1.1GB go? I am afraid that Dolby Atmos is gone. I did not use any compression. I just want to mux video & audio together without losing any bit of data...

Im using v8.4.0

Is there any software that can confirm that video has Dolby Atmos sound?

[Neroldy]

Maybe this one?
https://github.com/mbunkus/mkvtoolnix/wiki/TrueHD-and-AC3

[MalickT]

Thank you for your reply but I´m still confused:

Original source audio file is 4.1GB.
When I drag the file into MkvMerge it shows two tracks: True-HD and AC3. When I demux them separately, the output will like this:
TrueHD.mka is 3.18GB
AC3.mka is 250MB

Where did the remaining 670MB go?

[foxyshadis]

The magic of padding bytes and stream overhead. There's a roughly 4% overhead for m2ts compared to matroska, the rest is most likely padding bytes, zero frames, or other inconsequential streams muxed in; you'd have to use an MPEG stream analyzer to really dig into the specifics of what and why. As long as they decode to the right length, there's nothing to worry about.

[MalickT]

So I do not need to worry that Dolby Atmos effect is gone? I have heared that Dolby Atmos 7.1 has some additional data steam in the audio that creates the object-oriented audio effect. How can I differ from regular True-HD 7.1 with True-HD 7.1 Atmos sound?

[foxyshadis]

It is possible that a private stream is being dropped, or considered junk data. You need a stream analyzer to dig into what's in the input vs the output. Even with a simple hex editor, you should be able to track and compare chunks of non-zero data and find out if any big ones are missing on the mux side.

[nevcairiel]

The Atmos data is part of the TrueHD audio itself, its not a separate stream as such, so its rather unlikely that a muxer would manage to get rid of it without having an option explicitly to do that.