Look, Dom... A local arranger dealer here in the US already figured out the solution to your problem. Didn't need no fancy video cards, high end audio cards, and certainly none of that techno-babble you just said...

He simply ran a Zoom pocket recorder at the same time as his camcorder, hooked up to the arranger's main outs (or a simple mixer so you can do VO), then replaced out the camcorder audio with the Zoom's audio tracks in a simple video editor.

Simple, effective (listen to Frankieve's Audya demos, which sound better than anything Lionstracs has ever released), oh, did I say simple? You know, when you design the world's most complex arranger (or should I call it something else, now? ), perhaps you tend to look for the most technical solution to a problem. When you PLAY arrangers, you tend to look for the simplest solution that WORKS...!

Perhaps something to remember about your potential customers..?
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An arranger is just a tool. What matters is what you build with it..!