How to synch up audio to video on iMovie?

External audio recording, before you start, determine the audio bit & sample rate your flip is capturing and make sure your audio recorder can match it - bit rate & sampling rate,

8, 16, 32 bit
44.1, 48 khz sampling

if your recorder can't be "adjusted", yer outa luck, but chances are, you'll end up with the same issue, maybe a bit less, because the 2 units are "independently" measuring time.

Usually, the external audio starts out "in synch" then starts drifting. If you can deal with the aggro, shoot in very short clips - try 60 sec, see if it stays close, experiment. The shorter the recorded clips, the less "time" they have to drift apart.

As far as a better editor, that's not the core problem perse, although with the right hardware/software & enough coffe it can be dealt with

external audio has to be synched to the video recorder via "worldclock" - not the big thing in some bunker but a signal sent from the video recorder/camera to the audio recorder that says "we are in synch" - and that, well, money for hardware again. Basically, once machine measures "time" for both of them, so they both need the ability to manage worldclock

cheaper to buy a low-end HD cam that accepts an external mic, like the Kodak's, and a low-cost wireless lavaliere mic