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How do I route audio from Flash to JACK?

There are a couple of approaches here.

  1. systems that route audio from the web browser via ALSA: routing ALSA audio via JACK
  2. systems that route audio from the web browser via GStreamer: routing GStreamer via JACK
  3. systems that route audio from the web browser via PulseAudio: routing PulseAudio via JACK
  4. use the libflashsupport-jack library from Torben Hohn

The first three solutions that are described via the linked pages. The final one uses a little-known feature that Adobe provides in its browser Flash plugin: the plugin will (optionally) attempt to load a software library and use it for delivery audio data. There could be many different uses for this library, but in our case we only care about the one implemented by Torben Hohn which sends the audio onto JACK. Its probably the least-hassle, most reliable way to get audio out of Flash and into JACK.

Unfortunately, at this point in time (Fall 2010), most Linux distributions do not package this library, so if you want to use it you will need to build it yourself. This is not that hard if you've used the command line a few times:

git clone git://repo.or.cz/libflashsupport-jack.git
cd libflashsupport
sh bootstrap.sh
make
sudo make install
You need some tools installed for this build process to work:
  • ALSA development libraries
  • JACK development libraries
  • libsamplerate development libraries
  • libssl development libraries
  • basic software development package
  • git-core
  • autoconf
  • automake
  • libtool
If you are on a 64-bit distribution that uses /usr/lib64, you may also need to arrange a symbolic link:
sudo ln -s /usr/local/lib/flashsupport.so /usr/lib64

On some versions of Linux that use a web browser that looks for things in slightly different locations (Ubuntu Lucid is one example), you may also need a command somewhat like this:

sudo ln -s /usr/local/lib/libflashsupport.so /usr/lib/firefox-3.6.3/

After installation, quit any existing browser and then start a browser, visiting some Flash-using URL. Assuming that JACK is running, things should just work. Latency (the video/audio lag) is a little high - work might be done in the future to address this.