Using .mka in mkvtoolnix

[Binome]

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.

[ProWo]

Use clever FFmpeg-GUI.
Load your mkv, click main page, click encode audiostream, select your audiostream, click encoder.
Select your encoder, select the channels, set the bitrate and click encode.
If finished, click on multiplex, you will find all streams from your source mkv and the new encoded audiostream in green.
On the left, select all streams you want in your final video, set the output container and click multiplex. Done.

[Binome]

The name says it's a GUI but I see only commands in the "bin" folder.
How to use it?

[ProWo]

The name says it's a GUI but I see only commands in the "bin" folder.
How to use it?

ffmpeg is a video framework and clever FFmpeg-GUI is a graphical user interface (GUI) for it.
You need both.

[Binome]

Ridht, I was in thye wrong folder. Don't have time now but I'll try next week.

[jagabo]

In mkvtoolnix GUI load the original MKV file, disable the audio track. Add the new MKA file. Save.