[Tim Greentree]

Hi Zvonimir, it is possible that the left and right channels of the audio are out of phase. a tricky concept but bear with me. This is often hidden when listening in stereo, but is readily apparent when the audio is mixed down to mono (such as would happen when previewing on the camera only).

When you were recording the audio, were you using a professional 3-pin microphone, with an adapter lead possibly to a 3.5mm headphone jack type input?

Professional (shotgun) microphones have balanced audio outputs on XLR 3-pin connections. If you want to know what balanced audio is, google it, cos someone else’ll do a better job of explaining it. But the outcome is, if the cabling is wired incorrectly, you end up with the left and right channels having OPPOSITE versions of each other (like matter and anti-matter). This will sound fine when you are listening in stereo, because the two channels don’t mix, but when you listen through the camera speaker the two channels are mixed to mono, and the out of phase audio cancels out – and silence. So you may well hear the other sound effects but the main dialogue will be missing.

How to fix this? well, isolate which tracks are causing the problem, then try muting or deleting one side (left or right) of the track – so that only one of the channels is coming through (panned center).

Try that and let us know how it goes.
-Tim