www.makemkv.com

Hello everybody,
I have some .mkv files I want to make smaller by suppressing some tracks. I'd like to recompress the audio tracks so I extract them as .mka file. And then I use online compressing to get others .mka files.
Now I want to use mkvtoolnix to make another .mkv file from the original one. The problem is when inserting a .mka file mkvtoolnix finds a video track with no audio one so I can't import them.
Do you know a simple way to compress audio tracks of a .mkv file?
Thank you.

I'm trying to understand your situation. You have .mkv files with both video and audio in them? And you're tying to save some space by leaving the video alone but making the audio smaller?

As a percentage, the video in the .mkv files is very likely the largest thing. Consequently, changing the audio is unlikely to save a lot of space.

In any case, ffmpeg is probably the tool you should use. You can copy the video and transcode the audio with a single command line. For example: https://opensource.com/article/17/6/ffmpeg-convert-media-file-formats