When trying to open MPEG-2 files without an audio track, they can't be opened with Avidemux. I get an error window: "Cannot find a demuxer for file"
I've uploaded a test file without an audio track, so you can test it yourself:
mpeg2withoutaudio.mpg (http://www.file-upload.net/download-12068259/mpeg2withoutaudio.mpg.html)
It is mpeg ES, unsupported