Is there a good application in linux for attaching mkv videos. mkvmerge corrupts the videos with unusable output. Openshot has predefined output size while I have videos with non-standard dimensions.
You can use FFmpeg:
With a text file called mergelist.txt (or whatever you want to call it), i.e.:
file './file1.mkv' file './file2.mkv' file './file3.mkv'
you can use that as the input:
ffmpeg -f concat -i mergelist.txt -c copy merged.mkv