How do I start to create an online Video Converter?

Basically, I can create a video converter with ffmpeg and Delphi programming using Delphi XE2 or higher. I have been wondering for many weeks how can create an online video converter where visitors to the website can upload their files and convert them to say, AVI, format.

1. How do perform video conversion on a web?
2. Is is possible to run executable file on a website? (VIA INTERFACES, perhaps)

As I am familiar with Windows video converting system only, what do I need to connect an start running executable file to a web system.

I need a guidance to kick off.

Thanks!