I think someone mentioned that it is preferable to place the audio (eg music), first. Seriously folks, its the ONLY way. Discontinuities or mis-matches in the video may be papered-over by a bit of judicious editing. Discontinuities or bad-matches in music are impossible to do anything about. Two examples:- There is a local Beach on Dunedin's coastline called 'Tunnel Beach'. Initially, in the days before I wrote my own, I tried the exquisite little Scriabin F-minor Piano Concerto's slow movement, as background. It proved disarmingly simple structurally but, although I love-it-to-bits, the music/video match didn't 'do-it' for me on any level. I trotted out that old Mendelssohn War-horse 'The Hebrides Overture'. I didn't like the particular recording, lack of bass, so using my music software I reconstituted the entire piece from the original score, courtesy of a 'Sibelius' trial which I never took them up on. It worked like a dream; why wouldn't it, it is all about the sea, anyway? With the music in place on the timeline, I cut from the best of my shots into the timeline, able to guarantee hairline accuracy of the visuals to the music. Shown at our club, it produced several seconds of silence, before more than one member rose to their feet applauding. With the music in-place it was a breeze to get it right. No manipulation of the music was necessary, except that I cut out some repetitious bits. Second example:- A nightmare, which is still a 'work-in-progress'. Shots taken recently of two New Zealand sealions playing (for want of a better word), in Hoopers Inlet, a local feature. The 'action' consisted of them flinging themselves skywards like dolphins, and I mean 'skywards' at least body length out of the water in some cases before 'arcing' back. These are big critters, and its not just ripples they were leaving on the surface. But, the action was intermittent and unpredictable and could not be depended upon. And, there is the problem, the regular beats and rhythms of conventional music don't lend themselves to a 'match'. I have made a start, in that I have marked, in-time, the peak of each leap out of the water, with a single short timpani beat on a bare 'score'. I am able to locate those visually and audibly as my sequencer allows 'visuals' to be run parallel to the developing music. But there, I am stuck, until I have a further burst of inspiration. The entire sequence runs for approximately 90 seconds on-screen and was about 70 metres distant from me at the time of filming. The images are OK. I tried croppings and blow-ups of action peaks in 'Virtualdub' but there is little variation and the shots have become too pixellated for my liking. If real shoe-horning of image/audio together is necessary. the audio too may be tweaked, just a little, by using a DAW and running at slightly above/below 'speed' without altering the pitch. I use 'Reaper' for that, (and for most of everything else, as well, incidentally, as it is very straightforward to use, which is more than I can say for brands 'X' and 'Y').