We've been providing teaching webinars using GoToMeeting service. However, we are now trying to automate this process by playing pre-recorded 90 min webinars as a flash video. Our GOAL is that the audience still feels it is a LIVE WEBINAR (otherwise the attendance goes down). Usual attendance is 200-400 viewers simultaneously.

We tried using a streaming server and starting it at the advertised time, ie 6pm PST, BUT that is cost prohibitive.

>> The solution we need to create is to play a flash video based on the time a viewer joined; ie if a person came to that webpage 5 min late, the video would start 5 min in the presentation; if they were 45 min late, the video would start at 45 min in the presentation. That would give an impression of a live event.

One way we think it could be done is - on the webpage where the "live" presentation will be happening, there's a screen where the webinar will be playing with a countdown clock (starting from a few days from the webinar, counting down to the last second before the start).
When a viewer logs into that page, he sees the clock counting down, and at 00:00 the webinar starts.
The webinar (flash movie) should probably download at the beginning and not be streamed - this way we lower the cost of not having a streaming server. However, we need to be able to support a few hundred people downloading it at the time (if that is only constraint we may limit the attendance to 50 or less in that case).

Now, there has to be a code written that will start playing the flash movie based on when the user got to that page. If an user got there at 6:01pm, the webinar will start 1min in the presentation. If an user got there at 7:01pm, the webinar will start at 61min in the presentation. That way, the users/viewers have the experience of a live webinar.