Harry Potter site HP4U has posted a short set report from a young extra who participated in the Quidditch World Cup scene: "I don't remember seeing ANY of the Malfoy's and I didn't see an empty seat for Winky?"
While the report may not give us a lot of details, it does give us a little insight into what an extra may actually do on the set:
What really amazed me during filming was the use of only one camera?! Or so it seemed. I learnt there were many more but to make sure all of us 'extra's didn't look at them during filming they are hidden while we cheered on our teams. I had to follow a very small light darting around on a blue screen in front of me, which represented one of my Quidditch team players. It's weird but great to act knowing all the really cool backgrounds will be added in and it will look so different on film.
The stand itself we filmed on was 2 stories and about 30ft high. It was around 50ft wide. At the back of the 2 rows (one above another) there was a ladder type thing, which you will be able to see. We were all on the top level and there were other 'fans' coming up and down the steps during filming. I don't know what will be added to the front of the rows as it was all blue screen too.
Thanks to Sirius for letting us know about the report.