To be frank i think your tool has a better user interface than the MKVMergeGUI header editor.
Suffice to say it looks like i get an error message on the output tab once i try to process your suggestion (go to the right track number and edit the 'default' flag).
For some silly reason the command line seems to automatically adjust to my windows language but translated it says something like:
"Warning: The properties 'track:s4' and 'track:s4' lead to the same track with UID ######".
After that it still states "Changes are being written to file. Done."
But after that when i check the mkv file, nothing has changed.
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The MKVMergeGUI header editor has a few major turn-offs... opening as well as writing to a file make the window 'not responding' there's no progress bar or anything.
Editing the subtitle track properties is bothersome to say the least since you have to collapse the right headers and scroll up and down the window while that seems to work rather limited.
[Edit]:
Looks like your tool is working regardless of the output message!
The track properties are being changed...i just had to un-default the other ones for the changes to become visible (must have slipped me somehow).
