Ogg/vorbis streaming in 4 channels
One of the challenges for Radio Esperanzah 2007 was broadcasting in live the Monday special event with Manu Chao Radio Bemba.
On the stage, outputs were the same than for the other lives : stereo lines with the frontstage, two lines from the ambiant microphones.
No way for us to mix these 4 signals before sending them to our studio. Firstly, no space in the loaded sound setup : two huge Midas mixers are installed for the evening. Our small setup (PC tower, 1U compressor/limiter/cables) have just a place under one of mixers. Secondly, .. we don’t have the required mixer. A small Behringher UB isn’t the right device for the job.
So the main part of the problem was sending to our studio the 4 captured lines.
To make a stream cross through an abbey, you need a cable. With Bastien, the crazy guy which deploies the whole festival network, we link the frontstage to the festival network with something like two 50 meters cables and a 15€ switch. 9MB/s and less than 1ms, the network link is about perfect. We could test an UDP transpor. But the time is missing.
On the frontstage, the capture system is a simple (old) PC, a PCI M-Audio Delta 44 and a Behringher 4 channels compressor/limiter. Like always, the software system is on Debian. The streaming system is as simple as possible : icecast2 and ices2. The studio simply comes and retrieves the stream on the icecast2.
But the stream content is a bit special for this evening : ices2 creates a 4 channels ogg stream from the all Delta 44 inputs. 48000 Hz, a variable bit rate quality 8, with such settings, the bitrate makes peaks at 700 kBs 
At the studio side, we have to retrieve and play this nice stream. A first test with alsaplayer removes it from the candidates list : alsaplayer plays a strange mix of the 4 channel stream. No solution to play this stream to our jack server … After a small stress, we choose the most basic solution : use the second capture satellite and its Delta 44 to play the stream. The 4 outputs enter into our mixer. The player choice is as simple : ogg123. Indeed ogg123 plays fine the 4 stream channels and output them to the m-audio 4 outputs (via the alsa driver).
Bingo ! At 3 AM, Monday, we have our link system : 2 old PCs, 2 Delta 44, icecast2, ices2 and ogg123
Small bugdet for a good result. A thousand of listeners followed the live on the net, far more in Belgium via the various FM partners.
Tags: esperanzah, icecast2, ices2, m-audio, ogg vorbis, streaming
September 4th, 2007 at 7:49 pm
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