If you want to start a video further into the clip due to, for example, the events start further into the video than the broadcasting starts, you can do it in two ways depending on whether you do it on the play channel or if you have it embedded in a website.
The first way to do it is to enter the editing mode on your video, go down to the "Advanced" tab and select "Player" and at the bottom of it there is a box where you can fill in how many hours, minutes and seconds into the video you want to start. You can either enter the value "1m30s" or "90s".
The second way is when you enter the value in your embed code. Then you go to the bottom of the page and fill in the field where it says "Start time" in the same way. Either "1m30s" or "90s".