Add the audio afterwards in a video editing program like premiere or after effects. Flash is ill suited to the task of exporting any videos that are longer than 1 minute.
Thanks moccamaximim. I've tried that, but still it's poor quality. I've come across this page http://helpx.adobe.com/flash/kb/tips-reducing-dropped-frames-enhanced.html which is pretty helpful (I realized the problem is frames are being dropped), but I am not sure how to install the custom command the page has which might fix my probem. It looks like:
To install the custom command:
- Download videoPreferenceCommand.zip.
I am also going to try the trial for flash cs5 to see if that helps at all. Any tips specifically for reducing dropped frames would be great.