Weird extra audio track on Source Code [2011]

[Chetwood]

This BD comes with a weird commentary track: there's some explanations given by Caltec professor Sergei Gukov on scientific aspects of the movie. These are sprinkled throughout the movie on a separate audio track that DOES NOT have any other audio. Usually, if you watch the movie with director's comments enabled, you hear the regular track softly in the background which is getting turned up any time there's no comments given. But on this BD the entire track is silence except for when the professor is commenting. How does this work? Are these comments superimposed over the regular track by Java commands or something?

MakeMKV lists

Title 1:
Name: Source Code (English)
Source file name: 00000.mpls
Duration: 1:33:12
Chapters count: 12
Size: 24.6 GB
Segment count: 1
Segment map: 0
File name: Source Code_t00_s00000.mkv.

with these tracks

DTS-HD MA Surround 5.1 German
DTS-HD MA Surround 5.1 English
LPCM Stereo English

and

Title 3:
Name: Source Code (English)
Source file name: 00000.m2ts
Duration: 1:33:12
Size: 24.6 GB
Segment count: 1
Segment map: 0
File name: Source Code_t02_s00000.mkv

with these tracks:

DTS-HD MA Surround 5.1 German
DTS-HD MA Surround 5.1 English
LPCM Stereo English
DTS Express Stereo English.

[dcoke22]

This is the first I've ever heard of DTS Express. I did find this: https://github.com/HandBrake/HandBrake/issues/2501 and more specifically this comment:

You caught me as I was just looking over the sparse documentation for MakeMKV, to determine whether there was special handling available for the track. I can find none there, though leads in other forums seem to indicate that the DTS track is related to picture-within-the-picture entities and that it can be teased out with mkstoolnix followed by mkvmerge.

BTW, my rip of Source Code (2011) doesn't seem to have that track… or the rip was made with a too old version of MakeMKV to get that data off the disc.

edit: Also, this: https://www.synopsys.com/dw/ipdir.php?d ... _dts_hdlbr

… DTS® HD LBR (Low Bit Rate) Decoder, also known as DTS Express, is a mandatory codec in Blu-ray Disc™ applications for the secondary audio channel to provide stereo (2 channels) output. …

[thetoad]

google blu-ray secondary audio. the bluray spec has the ability to mix in a secondary audio track.

[Chetwood]

Yeah, found it, thanks. And of course, the BDA screwed up cause you just had to expect the lazy manufacturers would implement it like this.

[thetoad]

honestly, that makes perfect sense. I don't see how the bluray player could mix it it and bitstream. "at best" it could mix 2 pcm tracks together, but that's not really bitstreaming anymore. it also shouldn't make a difference if the player is able to decode the dts-hd or truehd track and play it as pcm. On the flip side, I doubt you would ever see it with atmos for the same exact reason.

[Chetwood]

Right, but it wouldn't be a problem to simply record the extra commentar in HD as well, you wouldn't need to use more than stereo and you'd still probably save space.