Recorded videos and I can't hear any audio. Is the audio there and I cant hear it, or didn't get picked up at all?

The other night I went to a concert and tried to record some videos on my iPhone 4. When I came home and watched them, there was no sound! So I tried everything from making sure it wasn't on silent, bluetooth was off, restarted it, tried opening it in a media player, and nothing. I even uploaded them to a computer and no sound. Then I tried to record a test video and when I did that, my audio was fine. Did I do something wrong when recording at the concert? And was the audio not picked up and I have nothing or is it there and I just can't hear it? Theres no buzzing noise or slight nosie, just completely silent.