Record ouput from jack

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This is a simple howto that describes how to record the output from any app directly using jack.

Prerequisites

To capture the output from jack, there is a nice and simple commandline tool called jack_capture.

emerge -av jack_capture

It can record to WAV or to FLAC directly. In order to encode to flac, you'll need libsndfile with FLAC support

USE="flac" emerge -av libsndfile

And of course we need jackd running.

jack-aware apps

This is easy. Just connect your app to jack and start playing. If you want the to record just what you listen, type

jack_capture

For more details see

jack_capture --help

non-jack-aware apps

Here we first need to define a pseudo ALSA device. Therefore we need the ALSA jack plugin

USE="jack" emerge -av alsa-plugins

Then we have to create or edit ~/.asoundrc (per-user) or /etc/asound.conf (system-whide) with following lines:

pcm.jackplug {
    type plug
    slave { pcm "jack" }
}

pcm.jack {
        type jack
        playback_ports {
                0 alsa_pcm:playback_1
                1 alsa_pcm:playback_2
        }
        capture_ports {
                0 alsa_pcm:capture_1
                1 alsa_pcm:capture_2
        }
}

Now we can test this with

aplay -Djackplug some.wav

Works? Cool.

Now we set the alsa device in our app (e.g. realplayer 10) to jackplug, and start playing and capturing.

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