91Èȱ¬

Coyopa, as any regular Radio Labs reader will know, is the new system for encoding 91Èȱ¬ national radio stations for the iPlayer and internet media devices - both simulcast and on-demand. It's been running well in production since November, and is now producing all listen-again and most simulcast streams across our services.

If you're deeply interested in the technology we use, here's a quick delve into rather more detail about Coyopa. This isn't for the faint-hearted, particularly if your tolerance for TLAs is low. (What's a TLA? A Three Letter Acronym. LOL. FTW!)

We have used broadcast-engineering principles to implement the new encoding system - such as resilient system design with backups, multiple power supplies, keeping digital audio linear all the way to the encoder.

For simulcast - live streaming - we take the audio directly from the broadcast chain which feeds DSat/DTT. This is passed through an audio router (for resilience) and then directly into an AES3 sound card. The sound card implements protection limiting in a DSP and carries out other functions such as detecting audio silence (failure alarms). Up to four radio station versions (eg "Radio 2 UK") are encoded on each machine.

For Listen Again, the process is divided into two functions. Linear audio is recorded from the broadcast chain for each radio station, non-stop, and kept for up to seven days. Producers can schedule their radio programmes to be available for Listen Again, by selecting the times/days and repeat patterns (rather like a professional version of a consumer ). The system will let you schedule "in the past" too, using its internal store of audio. Users can also select which regions will hear the audio (UK/International) and allow programmes to be automatically published after the show (some programmes have to be edited before being allowed through for compliance or rights reasons). There are different rights restrictions for download (podcast) files, which Coyopa will begin producing later this year, and for streaming files. Producers can also re-edit the programme, particularly the start and end times, at any time to tidy up the audio that listeners hear.

When a programme is ready for encoding, it is sent to a set of sixteen encoding machines, allocated according to the current workload: Radio 3's Through the Night (nearly 6 hours) takes longer to encode than a fifteen-minute news bulletin, after all. Up to four files can be sent for encoding for each radio programme (UK/International, Streamed/Download), and the encoding system knows which formats/bitrates to use for encoding each file. After encoding, the many different encoded files are passed, using , into a large store, which then clones the files to our content delivery partners.

The schedule of radio programmes compounds the encoding workload by having many programmes across the radio stations ending at about the same time; nevertheless, the whole process is designed to be automatic and fast.

The server hardware uses HP "Blade systems" - where each PC server is a plug-in module, with up to 16 in a, very heavy, chassis. Six power supplies share the load of the whole rack, fed from two different sources of mains power. These servers are used because as well as offering the performance, they are reliable, easy to maintain and allow a very high packing density. Each server has two 4-core processor chips which are needed to achieve the throughput for listen again encoding.

As you can see, Coyopa is rather more than a little machine with a sound-card!

I hope all that was interesting to some; and I'm indebted to my colleague David for working on this blog post with me.