Use ffmpeg.exe based on command line from Jay_UK's.
Merge remote-tracking branch 'remotes/origin/master' into BUG-3920_mtn.exe_does_not_generate_thumbs_for_all_video_files
Merge remote-tracking branch 'remotes/origin/master' into BUG-3920_mtn.exe_does_not_generate_thumbs_for_all_video_files

Conflicts:
	mediaportal/Core/Util/Util.cs
Kill ffmpeg process for installer.
Merge branch 'BUG-3920_mtn.exe_does_not_generate_thumbs_for_all_video_files'