[Soli]

While it's possible to have an interleaved TrueHD and AC3 track, I thought the vast majority of BD's had separate TrueHD and AC3 tracks, since interleaving them is not a requirement in the same way there is a DTS core plus extensions which then give DTS-HD.

It's a requirement. But usually left out when downconverting to mkv as it takes up unneccesary space. With Kodi transcoding to AC3 makes this problem more of an academic art.

Note that the core of THD is not really a core, just interleaved with THD, but fully independent. Not like DTS where the DTSMA/DTSHD part is an extension of the core (even though it's possible to encode DTSMA without the core altogether).