Quite a lengthly Q&A about BBC iPlayer. Some of the stats are crazy though -
http://news.cnet.com/8301-1035_3-10237793-94.html?part=rss&subj=news&tag=2547-1_3-0-20
During peak hours, BBC iPlayer pumps out 12GB of data every second, and 7 petabytes of data every month.
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We create about 14 different formats, ranging from about 160Kbps for some mobile, over-the-air streaming, through to 1,500Kbps for our highest iPlayer SD quality stream, in H.264 played out as Flash. We also create 3Mbps (for standard definition) on Virgin Media, and now for our HD content we create 3.2Mbps HD. So it's about 14 or 15 flavors.
http://news.cnet.com/8301-1035_3-10237793-94.html?part=rss&subj=news&tag=2547-1_3-0-20