"parent" and "child" audio streams?

[eddified]

Many times ripping blu-rays, I see what appears to be "parent" and "child" audio streams. See:



In this case, the questions are:

1. Are the child audio streams are generated by MakeMKV using the parent stream as source material, or do the child streams actually exist on the disc?
2. If the child streams are actually on-disc, what about it makes it a child stream? Does the metadata on the disc designate the 'child' audio stream as representing the same audio that the parent stream does, but at a lower quality?
3. Why might there be two DTS master audio streams in English (see above image?) I understand that there could be a descriptive audio service for the blind, but usually that won't come encoded as DTS-HD 5.1 Master Audio, right? What is a reasonable explanation for there being no less than three (3) 5.1 English streams in the above case?

[Woodstock]

As I've read here, the DTS "core" streams are within the DTS-HD, but the MKV standard doesn't allow selecting the core if it isn't its own stream. So it's one stream on the disk, but, if you want both to be available at playback, you have to select both.

Often there are commentary tracks. But, in this case, you have a 7.1 and a 5.1 audio stream, which are distinct entities. What is REALLY interesting is getting disks where there is a 2.0 channel main audio stream, and a 5.1 HD commentary... which sometimes gets selected as the primary audio stream, because it is "higher quality"!

[eddified]

Does selecting both the child and parent streams cause the title to take more space on the HDD than it took on the BD?

[Romansh]

Does selecting both the child and parent streams cause the title to take more space on the HDD than it took on the BD?

Yes in the case of DTS-HD. No in the case of Dolby TrueHD.