Re: getting gstreamer and jack to play ball

theo <theo_linuxaudio@xxxxxxxx> · Wed, 03 Feb 2016 01:02:45 +0100



    On 02/01/2016 05:12 PM, Paul Davis
      wrote:

    
          On Fri, Jan 29, 2016 at 6:29 PM, Neil
            C Smith <neilcsmith.net@xxxxxxxxxxxxxx>
            wrote:

            
              On 29 Jan 2016 22:47, "theo" <theo_linuxaudio@xxxxxxxx>
                wrote:.

                > - What is the point of this (re-)connection
                behaviour of gstreamer? - gstreamer doesn't suddenly
                become a "new device" when it starts playing a new song.
              Well, in some ways it does, depending on how
                you're using GStreamer. I've been having fun with this
                issue recently too.
              This is all down to the default behaviour of
                the GStreamer JACK sink. There are two properties that
                can be set on it that may be useful. The first, connect,
                controls whether GStreamer auto-connects to the outputs
                - I think using connect=0 will stop it auto-connecting.
                More recent versions of GStreamer also allow you to set
                a port pattern for auto-connection, which would allow
                you to control the behaviour you want without the
                patchbay.
            
            
            Slightly more than this: almost all gstreamer-enabled
              applications consider various user operations like "Stop"
              (and sometimes even "Pause" and sometimes even "Next
              Song") to be a point at which they disconnect from
              whatever audio backend gstreamer has been told to use.
              Specifically, they "close" the "device".

              
            The gstreamer backend was written to disconnect from
              JACK when told to "close". This behaviour makes sense if
              the "device" was an actual physical device, but it doesn't
              make any sense in the context of a server like JACK. 

              
            I did try to patch the gstreamer JACK code to not do
              this, and remain connected to JACK across time and space
              (so to speak) but it was harder than I was willing to deal
              with.

            
    Hi,

    
    Sorry for the late reply. Got a lot of work dumped on my desk.

    
    Well, come to think of it, maybe it is just easier coding to
    close/reopen. I don't know what would happen if a program would
    leave an audio device open only to find the next file to play
    inaccessible or something like that. I guess that would require
    extra checks. AFAIK, the close/reopen also does not result in
    audible issues.

    
    Thanks a lot for the excellent hints. I had a look at the GStreamer
    properties and control=0 indeed does the job.

    
    for posterity:

    
    I edited properties using gconf-editor. By setting the following
    keys:

    system->gstreamer->0.10->default->audiosink

    system->gstreamer->0.10->default->musicaudiosink

    both to

    jackaudiosink buffer-time=2000000 connect=0

    (or jackaudiosink buffer-time=2000000 connect=none)

    I got playback through jack from gstreamer without the default
    connection to channels 1 and 2 of my multi-output sound card. By
    making the required connections (in my case to channels 3 and 4) in
    the qjackctl patch bay everything just works (tm).

    
    I also had a look at the gstreamer code, and got completely bogged
    down trying to set up a working gnome build environment. I'll have
    to leave that for now. (It also should be noted that this is for
    gstreamer 0.10 - I have no idea how this ties into gstreamer 1.0)

    
    thanks again.

    
    cheers, Theo

    
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