https://helpdeskgeek.com/how-to/open-command-prompt-folder-windows-explorer/
https://www.architectryan.com/2018/03/17/add-to-the-path-on-windows-10/
The Path environment variable can be edited in "User variables" (or created, if it doesn't exist) or in "System variables". After updating it, the existing Command Prompt window must be closed and reopened in order to to find a new console program.
After installing, add the folder that contains espeak.exe to the Path environment variable. In my case it's C:\Program Files (x86)\eSpeak\command_line.
To test it, open Command Prompt, for example, with Win > cmd, type espeak --version and press Enter.
On Windows it can installed by downloading ffmpeg-git-full.7z from https://www.gyan.dev/ffmpeg/builds/ and unpacking it somewhere using 7-Zip File Manager.
Add the folder that contains ffmpeg.exe to the Path environment variable. In my case, it's C:\Programs\ffmpeg\bin.
To test it, open cmd and type ffmpeg -version.
