MKVToolNix can't join LOTR UHD parts

[ContinuousPalace]

The Lord of the Rings Extended Edition discs split each movie into two parts. With the Blu-ray edition, I used MKVToolNix GUI to merge the two parts. But when I try with the UHD edition, I'm getting a "Appending tracks of this type is not supported." error.

Here's what I'm doing, just in case I'm somehow doing it wrong for UHD. (It has been a few years since I merged my Blu-ray parts and I can't find my Bly-ray movies, so maybe I'm just remember how to use MKVToolNix wrong...)

1. From the Multiplexer icon under the Input tab, drag part 1 of the movie to the source files box
2. Right-click part 1 in the Input box and choose "Append files"
3. Choose part 2 from the File Explorer.
4. Click Start multiplexing

After about a second, I get an error in my logs: "Appending tracks of this type is not supported." (I've also attached the "Normal output" as a file here.)

As far as I can tell, MKVToolNix does support UHD. At least, there don't seem to be any sites claiming that it doesn't. And I doubt that LOTR has something crazy going on.

Any idea what I'm doing wrong or where to look next?

[dcoke22]

https://www.makemkv.com/forum/viewtopic ... 45#p100573

Folks in that thread claimed to be able to merge the extended editions of LotR UHDs.

[ChisumMP]

MKVToolNix cannot join files containing flac streams, therefore "Appending tracks of this type is not supported". Your log shows at least one flac stream.

[Chetwood]

So let me get this straight, the LOTR extended editions are even too large for one UHD disk?

[ChisumMP]

Yes, same with "Lawrence of Arabia" and "Gandhi" 4k's.

[necrosis]

Has LOTR ever been on one disk?

[liechsowagan]

Has LOTR ever been on one disk?

The Theatrical Editions, yes. The Extended Editions, not to my knowledge.

I own the DVD "bound book" and UHD editions of LOTR, and the UHD editions of The Hobbit. The UHD Editions include Theatrical and Extended Editions separately.

For the LOTR trilogy, there are 3 UHD discs for each title; 1 for Theatrical, 2 for Extended.

The Hobbit UHD Extended Editions fit on a single disc, so there are only two discs per title.