Are these audio tracks identical?

[ACoffee12]

Hello,

I have noticed that several of my Blu-Rays with Dolby Atmos tracks have a Dolby Digital 5.1 track nested under the Atmos track as well as an additional DD 5.1 track. My usual rule of thumb is the save the best quality 5.1 track available, but I can't tell what the difference is between these. Anyone know if there is a difference or which one would be better quality?

Screenshot from 2020-12-07 20-09-24.png (136.43 KiB) Viewed 10297 times

Thanks

[preserve]

The nested tracks are the lossy core of the lossless audio.

The additional tracks will vary, and you should check what the packaging states or the specs/review on a site such as Blu-ray.com. They could be an additional mix as lossless (5.1 as opposed to 7.1), although on this disc that additional track is lossy, but they could also be a Descriptive Audio track. They could also be a commentary, although I find it’s rarer for commentaries to be 5.1 or lossless, they are usually DD Stereo.

[preserve]

Assuming that's the US release of Wonder Woman, that second non-nested 5.1 track is indeed Descriptive Audio, as per the back of the case.

So if you want 5.1 instead of 7.1, the nested track would be the one you want.

[ArArdin]

BD specs state that it's mandatory for TrueHD audio to have an embedded AC3 track.
Often this track is encoded @ 640 kbps, the maximum value allowed for legacy AC-3 on blu-ray.

[ACoffee12]

Thanks for the clarification! I was initially confused because of the checkbox hierarchy; I thought I would have to include the 7.1 track in order to get the nested 5.1 track. But I guess they just structure it this way so you can tell which track is which...

Thanks again.

[ArArdin]

Note that this is for TrueHD only. The TrueHD track itself is independent (as is the embedded AC-3 track). The mkv container can only mux this "standalone" TrueHDtrack as one audio track. So without the embedded AC3 track. Should you want this track too, you're bound to mux it as an additional track.

A well known "complaint" you'll read on the internet is "not having sound with TrueHD from mkv, whereas with TrueHD from a full disc rip everything works".
Often the issue in these cases actually is that the embedded AC-3 track (which is mandatory in TrueHD blu-ray) is being played back and that's what people hear. And hearing nothing from the mkv because the legacy AC3 track simply wasn't muxed into the mkv.

DTS-HD Master Audio is different in build-up. Such a track has a lossy dts core. Next to that core there is additional, dependent data. This core plus the additional data together make up for the DTS-MA. Contrary to TrueHD and its embedded track, such a track can be muxed as one track in a mkv-container.
Lot of people find this handy: playing back your mkv without having to worry about having chosen the right audio-track. Thereby, a lot of mediaplayers (I think the most, if not all) that are not HDMI-connected but via SPDIF, will bitstream the dts core through the optical or coaxial connection.