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Live audio video broadcasting

This page describes the basic conditions how a set up should be build for an application similar to xmeeting or skype. This mainly concerns how to synchronize audio to video, and a way to prevent audio feedback.

Audio synchronize

Because the videocamera produces a stream of images with a slight delay (iSight with about 170 ms), the only possibility for audio to be in sync with the video is to delay it. This can be done completely with software, not requiring additional hardware.
Following software should be installed:

  • Xcode tools (This brings AU Lab, which incorporates a delay function)

Follow these steps

  • Start JackPilot
  • Start AU lab (/Developer/Applications/Audio/), leave the 'Create New Document…' window as it is. This will come later.
  • Build an aggregate device
    • JackPilot→Menu: “Open Audio MIDI Setup…”
    • Audio→Menu→Open Aggregate Audio Device Editor→Merge Built-in Output and Built-in Onput into one device, Set clock to “Built-in Output”
  • Configure the audio input source. (Macbook Pro's line-in)
    • On the main Audio Tab→System settings, Default Input: JackRouter (This is where your audio source should refer to)
    • On the main Audio Tab→System settings, Default output: JackRouter (You can ignore this, the use of this is now not important)
  • In the small JackPilot window which shows the number of JackConnections and the CPU Load, click on Start. Then click on Routing
  • In Au Lab, set preferences, to output sound to the virtual Jack Audio rail
    • Preferences…→Devices→Device: JackRouter
  • In Au Lab, create a new Document. For the delay-effect, you will only need to create one channel
    • Audio Device: JackRouter
    • Inputs→Add input→1
    • Output→1
  • in the Jack Connections Manager, create a stereo connection from line-in to Jack in
    • select in column 'Send Ports:' system, capture_1 and in column 'Receive Ports:' AU Lab, in1. Doubleclick on one of them, to establish a connection.
    • Repeat previous procedure for the other (Right) channel.
  • Audio Engine running?
  • JackPilot actively Routing?
  • Start the application which should receive the delayed audio (e.g. Skype or Quicktime)
  • Now route the Au Lab output to the application input

Bluetooth audio output

  • Route the audio output of your Mac to your BT device
projects/audiovideo/broadcasting/index.txt · Last modified: 2008/05/14 17:54 by