On Friday we attempted our first live recording and streaming session at the café. To the soft sounds of acoustic flamenco guitar, we gave life to our little Frankenstein’s Monster with a jolt of electricity.
I had bought myself a small Beringer mixer for the occation, with two microphone preamps and some cables. Unfortunately, I forgot the microphones, silly me. That mean we had to come up with a MacGyver solution, pulling the longest mini-jack cable straight across the room from the on-stage mixer, duct-taping it to the ceiling. The cable was broken, of course, giving us sound in one channel only.
Amature sound tech problems aside, it was a great opportunity to start experimenting with the video compression and streaming. The DV camera delivers 25 Mbps over FireWire to the MacBook running Quicktime Broadcaster. QT Broadcaster then encodes and compressed the video to 640×480 resolution at 30 frames per second, with a key frame every 60th frame. For good measures I clamped the output bitrate clamped at 1300 kbps, not that it ever exceeded half the rate.
Darwin Streaming Server was running on my Ubuntu laptop. It read the live stream from QT Broadcaster, and sent it of to another computer on the local network, where it played back in a Quicktime web browser plugin. Neato:-)
H.264 is easily one of the best codecs around, giving supreme quality at lower bit rates. We confirmed this by comparing against an older MPEG-4 codec. To us the H.264 seemed to create crisper and higher contrast images even at half the bitrate.
I learnt one thing in particular from this first session: live video compression places higher demands on the hardware than offline compression.
The dual core Intel MacBook was pegged at 80% throughout the entire session. When the hardware resources are maxed out like this, the encoding algorithm has to trade quality for efficiency, resulting in sub-optimal compression. Unfortunately it shows:-( It turns out that Quicktime H.264 encoding and Intel-based Macs may not be such a good combination after all.
Several costly high-end hardware-based encoding products exist, of course, but the affordable 99$ Turbo.264 USB 2.0 H.264 hardware encoder from Elgato naturally caught my attention. Word has it that they’re working on a live encoding version for use in programs like QT Broadcaster. Somebody heard my prayers.
0 Responses to “It’s aLive!”