[primaeval]

Try with a simple video link like big buck bunny to see if it's your stream that has problems.
http://clips.vorwaerts-gmbh.de/big_buck_bunny.mp4

Make sure the ffmpeg path is the full path.
The environment variables don't make it through kodi to the addon.

If you're trying to record on an external or smb path you need a version of ffmpeg that has been built with that support.
You also need to use the "ffmpeg Recordings Folder" with the command line version of the path to the recording folder.
Kodi passwords  for network file systems probably won't make it through to ffmpeg either.

Make sure the tvg-id value matches the channel id exactly in the xmltv file.