This question comes up periodically. You're shooting a band playing live somewhere. How do you handle the audio?
The only way to get even half decent audio is to record a board mix and use your camera mic for fill in ambience (provided the camera is anywhere near the right place). In a perfect world you'd get a multitrack master from the sound board with every instrument and vocal on a separate track. You would then remix. The reason? The live mixer (and audience) are also hearing what sounds are happening that the mics and direct boxes are not hearing; bleed from guitar amps, drums, etc. Without all of that, your mix will sound like it's missing something...because it is.
The Q&D way to do it is to try to get a split mix from the house guy to a separate recorder; instruments to one track, vocals to the oher and then combine that with some of your camera mic. The problem is he doesn't have time to do two really good mixes at the same time.
If you got to my online archive, there are two mp4 clips from a recent Karyn Oliver shoot. The shorter St. Mary's clip is just the camerra mic. The Rain is a postproduction mix of two channels from the board plus the camera mic.