Best format for the web

[rebels_mascot]

Hey, I'm creating a website for a college project (programmed in c#) which will allow a user to upload videos and play them back.
I'm wondering what's the best format to play back in? i.e. if they upload an avi or mpeg I want to convert that file to a format thats fast to download/stream but has good quality when they play it back?

Bit of a programming question here, whats the best time to convert the file in your opinion? The site is actually going to be an online file manager so the video may never be play backed online. So should I convert when the user uploads the file or convert when they want to playback the file?

I know this is a video site but I plan on doing the same with audio and image files if ye have any advise on the best formats for them aswell.

Thanks in advance for any advise.

[Baldrick]

Convert to flash flv using for example ffmpeg. Decent quality and fast conversion.

Converting when they want to playback the file wont work that well cause it take some time to convert. Maybe the user has to select that just that uploaded video should be converted.

[rebels_mascot]

Hey thanks for the reply Baldrick, thats a good idea. Could give them the option to just convert a file whenever they log in aswell.

Ya I thought flv would be the best aswell, not an expert so I said I'd ask to be sure.