I'm a designer and fx artist in the entertainment industry. I've been putting together a business plan and designs for a site. It's a rather large venture so I'm breaking it into pieces to see if I can make it happen.
It should load the sequence from a folder and cache them for realtime playback. it should be easy to point to different sequences so in the future it can be a pushed from php/mysql.
It needs to be able to run at standard frame rates ie.. 24 frames per second, 23.98fps, 29.97 fps, 25fps, 59.94 fps, etc.
It should sync with audio so there would be a mp3/wav/aac/ whatever, audio file in the folder that it would load as well and they would play in sync.
it should play forwards and backwards. And report what frame its on and how many are in the sequence.
you should be able to scrub in real-time, so as you drag the video updates, not like youtube or anything else where you have to let go of the mouse before it updates.
These are the very basic features that the player would require, if you think you're up to the task lets talk.