Question: I am looking for a solution to control my computer mouse just with my hands and a webcam. The goal is to combine it with voice input to let me move more freely in front of my desk.

It should support the usual mouse actions:

* position mouse pointer, left click, right click, middle click, scroll up, scroll down
* optionally: scroll left, scroll right

Answer: 
You can try Kdenlive. From their site:

> 
> Multi-track video editing  
>  Kdenlive allows you to use and arrange several audio and video tracks, each one can be locked or muted to your convenience.
> 
> 
> 

[Kdenlive | Libre Video Editor](https://kdenlive.org/en/download)

[Wikipedia link](https://tr.wikipedia.org/wiki/Kdenlive)

[![Kdenlive screenshot](https://i.stack.imgur.com/xlDOP.png)](https://i.stack.imgur.com/xlDOP.png)

I couldn't understand what you mean by "simple merge" but you can use command line tools like FFMpeg.
[avidemux](https://en.wikipedia.org/wiki/Avidemux) can add .mkv files at the end of each other.

Usage: Open the avidemux GUI, drag-and-drop the first .mkv file, then the second, then press "save" and enter the filename you want for the output file.

The input files must have the same size and encoding.

Available for Linux, Mac, Windows.

It is free and open source. It uses ffmpeg's libavcodec library under the hood.