I've been down the road of building an on-demand video product, from scratch and at great expense, prior to testing the market. Our company took the "if you build it, they will come" approach, which in hindsight, not surprisingly failed.

In my experience, building the technology and platform are the easier parts of the puzzle, especially today, when repurposing and integrating existing services is a very real possibility. Back when I was doing the VoD company, the technology to deliver online video was in its infancy, so we had to build the product by piecing together immature video delivery solutions, building the delivery platform from the ground-up.

I'd say choose your niche first, by defining the problem you are trying to solve, i.e. defining the gap in the current video conferencing market that you're trying to fill. Validate the niche by finding an initial set of just a few customers who have expressed a real need for your product. Talk to a few of them to find out what pain they are experiencing and define your project accordingly.

Once you've done that, start small and stitch together your MVP with existing solutions. Focus your efforts on the layer of value you're adding to solve the problem in your niche and defined by your customers, leaving the details of the underlying platform to the experts who are investing a lot of resources in building these platforms for third parties, like you, to use.

Hope that's helpful and good luck!

Always happy to discuss further on call as well...Chris