How to identify dual mono?

[pissed]

Many old films, pre 1990s, we recorded/released on vhs with mono audiotracks, but now these are ported to DVD, the soundtracks are duplicated and presented as stereo. I'd like to know how to identify these dual mono tracks - ones which consist of two identical audio streams.

[Overdrive80]

I'm no expert but you could just try to export each channel audio track to a file and see if they have the same crc. Maybe so you know if both channels are equal, when used as pseudostereo

[mp3dom]

A quick method could be to invert-mix the left channel into the right channel (or viceversa). If both channels were the same, the resulting track should be completely mute (so it's even easy to see)

[pissed]

Thanks for the replies; I used that invert-mix method (never heard of it; googled), resulting in a horizontal flat line:
http://i31.tinypic.com/2zirf6f.png

I guess that indicates that there is no difference between the two streams, confirming it is dual mono?

[mp3dom]

Yes, it should be dual mono.

[pandy]

Same can be with stereo coded audio - dual mono is ALWAYS signaled in header

[Ghitulescu]

There is another "dual mono": analog stereo captures of mono material. Chances are that the channels were already normed so an invert-mix can point this as well.