Hi all-
I'm tired and fed up after hours getting nowhere, so I'll make this brief.
I have an avi (XivD) plus sync sound (mp3) which I transcoded from a ripped DVD using ffmpegx.
I also have the same film's director's commentary which I would like to mux into the avi so the file as a dual layer option.

The technique for doing this in ffmegx is (as I understand it) supposed to be extremely straightforward (Tools, mux, select Audio and Video to be muxed, select Avi + audio as output and click mux).
Yet when I follow this simply procedure, I am not prompted for a filename or save location. Instead the progress bar opens and spins away without creating a file or recording any activity whatsoever in the log.

So I tried muxing the two files in avidemux, and although the avi it spat out was larger (and by more or less the correct amount) than the input, suggesting a second stream had been added, when I imported the new avi into MPEGStreamclip and analysed the file data, it only showed one audio stream.
VLC seemed to recognise two streams, but I couldn't find any way to actually play the second stream (the audio track option in the dropdown menu was grayed out).

Why is ffmpegx not muxing the video and audio as it is meant to?
Is the second audio stream muxed into the avidemux output and if so, how on earth do I play it?
I've tried DivX player, VLC and Mplayer OSX and I can't find an offer to select one of the two tracks anywhere.
Any advice much appreciated.