iPlayer uncovered: What powers the BBC's epic creation?

What kind of hardware powers the iPlayer?

"We've got about 60 encoding servers. And they're typically dual Quad Core Intel Xeon machines, and they run on a NAS backend architecture because the media that comes in is encoded at 50 or 100Mbps, and these files are many gigabytes in size. We make 400 hours or more a week.

"We will have a system where our schedulers log in and say which platforms each programme may be available on. Then our automated systems get the media file and encode it in all the ways that are allowed. After having been encoded, some files are set to download from BBC Web servers, sometimes they will be played out as Flash programmes and they'll be distributed to content delivery networks like Level3, Akamai or Limelight, and sometimes they'll go to special Real Helix servers which deliver content mostly to streaming mobile devices.

"Content is delivered broadly in one of the first two ways. When you download something directly from the iPlayer, those broadly come from the BBC's servers, which are operated by Siemens. There are two facilities in the UK, and they're set up in a failover way, so if one of them goes down or the power goes off, we can continue serving from the other.

"For streaming media we typically use the content delivery networks, and they've got edge servers located around the UK and in fact around the world. But typically we endeavour to make sure media is served from out of a UK location just because you get a better user experience.

"However, it may turn out that perhaps on a big night where everyone is watching The Apprentice, the content-delivery networks' local UK servers get maxed out, and they begin delivering from a server in France. These networks are set up to essentially load-balance, and it may turn out that there's no penalty to serving from France, than serving from London's Docklands.

"Where possible we try and have the content encoded before it's needed to be available in iPlayer. Our rights framework says that we're allowed to make programmes in iPlayer one minute after they finish on TV. So what we try to do is pre-encode the content so when it finishes, we can flip the switch and make it available.

"In reality, for those programmes it takes about 15 minutes to turn up in iPlayer because of the way pages are cached and so on. For programmes we can't have pre-delivered, which is stuff like news and sports and live things, as well as some programmes where the tapes are delivered only mintues before it goes on air, we do a live ingest.

"What happens there is it gets encoded off our 50i or 60i feed, and then it gets manually trimmed because when you press play in iPlayer it starts exactly on the frame where the programme starts. So we manually trim and then it goes to the encode, and that takes a few hours. So for some content it's available within minutes of it finishing on TV, and for some content it's typically one to two hours later.

"We know the audience wants content instantly after it finishes, and in fact we're doing a lot of work to make those times faster."

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