Does anyone know of any good websites that provide documentation on the mkvmerge commands? I have tried asking the developer of MKVToolNix about adding automation to the application but he tells everyone to script it yet he doesn’t understand that there are people who do not know how to code scripts. His definition of easy is not compatible with 99.99% of people and he provides no resources on what commands are available.
MKVToolNix documentation (click on mkvmerge, mkvinfo, mkvextract and mkvpropedit respectively to see the applicable documentation; same for `mkvtoolnix-gui´ if you’re interested in looking into some start options):
https://mkvtoolnix.download/docs.html
I just finished ripping and joining all 3 of my LOTR Extended version 2 disc set blurays the other day using theMKV Tool Nix GUI . worked great. a bit of a process for sure.
I can confirm there is a few seconds of gap/nothing in between the 2 parts but no big deal. I dont want to try and trim the video down to make it more seamless. it really is the 2nd half of the journey anyways so…good to have a pause there thematically 
I had to discover that it is kind of a deal if you want to transcode the audio or want to make subtitles fit. I’ve stumbled on this when I tried to make a stereo audio track (with dialog normalization applied), but it always went out of sync after the break from part 1 to part 2.
But there is a solution which again uses MKVtoolnix.
Use the “Split files” method from the companion post of this one here: [HowTo]: splitting multi-episode files with MKVtoolnix GUI
I used it to remove the over-long silence from the end of part 1.
Which then (after I’ve put the two parts together) allowed me to create my stereo audio track which stays in sync over the whole play time.
WARNING:
If you join files this way, and the audio is an Atmos track, if you play back on NVIDIA Shield, the audio and video will go out of sync during playback at the join point. You create a “seamless branching” … bug… which Shield doesn’t handle.
Unless there is an actual bug in MKVtoolnix, applying the method I described just above might be able to mitigate.
According to the developer of MKVtoolnix, it has no bugs.
And according to him he will never feel “motivated” enough to fix this.
But, yes, there is a “bug.” Try it yourself and see. It is very reproducible.
There are some of us who’ve been complaining about this for years, on deaf ears.
But @OttoKerner what you’re doing is essentially manual creating a seamless branch by joining in TrueHD in MKVToolnix. This problem is highly specific to Atmos, and it may be specific to Atmos+UHD, I’m not certain (I’ve never run across seamless branching problem in non-4K discs, and I have never tried to MKVToolnix merge two non-4K Atmos files.)
A good test: merge part 1 and part 2 of Zack Snyder’s Justice League 4K discs. The audio goes out of sync right as they’re exhuming superman, if playing the merged file back in bitsreamed Atmos on Shield. If you try any other player, and/or don’t bitstream the audio, the audio stays in sync. For Shield, and for audio/video sync, one must use pt1/pt2 naming and keep the files separate.
It (your method) works fine in every single instance. EXCEPT if you try to join tracks that have Dolby Atmos. Then seamless branching bug will appear.
