allow people to buy audio track from a video

one of the ideas I had was that people might play a video and want just the audio track. you might want to have a feature where someone can buy just the audio track at a reduced price, such as 25% of the price of the video.

A long long time ago it was standard to NOT have audio tracks on stock footage whatsoever. If you want to sell audio, render it out separately. The whole audio "radio button" thing is more of an annoyance. By default audio should not be included. But nowadays many do for what ever reason. A feature such as this would not be easy to implement nor would it be cost effective in the long run. For the few, and I would guess very few times it might be used, it wouldn't be worth it.

"A feature such as this would not be easy to implement"

I am a computer programmer, and have been since 1982. it would be easy to implement. it would take me 1 minute to write the code to strip the audio from a video.

and here is a basic example:

mplayer -dumpaudio -dumpfile clip_track.mp3 clip.avi

Good to hear you are a programmer and properly financially don't rely on footage sale. We do..

why separate them, they can just use it from the free preview ;)