When using jack server, musescore follow the jack master bpm even if jack transport is disabled

• Aug 6, 2019 - 14:31
Reported version
S4 - Minor


I'm using Musescore with the following revision (stretch-sloppy-backports):
OS: Debian GNU/Linux 9 (stretch), Arch.: x86_64, MuseScore version (64-bit): 3.2.3+dfsg1-1~bpo9+1 (Debian stretch/amd64), MuseScore build number not set, revision: d2d863f

When using the jack server, musecore follow the jack master bpm instead it's internal tempo, even if is the jack transport is disabled.

Step to reproduce :

  • Start a jack server (i hopeyou know how to do it)
  • run musecore, go to edit>Preferences...
  • in the I/O tab:
    • check JACK Audio Server
    • uncheck "Use JACK Transport" and "Timebase Master"
  • load a score in musescore
  • display the play panel
  • Run hydrogen
  • In Hydrogen enable "J.TRANS" and "J.MASTER" (see red circle on my capture)
  • set a bpm, different from the scare loaded in musescore
  • press the play button of hydrogen
  • go back to musescore ans see the play panel.
    The played tempo is set to the hydrogen bpm and you can't change it. The expected behaviour is to ignore the hydrogen tempo. Musescore should follow jack master tempo only if "Use Jack transport" is check and "Timebase Master" is uncheck.
Attachment Size
Capture du 2019-08-06 15-12-44.png 83.75 KB


Reported version 3.2 3.4

Same problem with Ardour 5 and Musescore 3.4.2, jackd2 1.9.12, Debian 10:
In Ardour: if checkbox Session/Properties/Timecode/JACK Transport: Ardour is JACK master
is checked and "Use jack transport" is unchecked in Musescore.
This bug can confuse users if any JACK client broadcasts timecodes by default (like Ardour), so whenever Musescore and Ardour happen to be run on the same JACK server Musescore's tempo gets locked, until users disable being master in Ardour (or enable master in Musescore).

Reported version 3.2 3.5

Running both 3.2.3 from Ubuntu 20.04 and 3.5.2-Development compiled locally. Both have same behavior. My timecode source is Carla. Notably, the Play panel slider for tempo is locked at a single tempo and cannot be moved with the mouse. If the last tempo was expressed by a Tempo text, it will be locked to that value. If the last tempo was set by JACK transport, it will be locked to that value.

I would expect the tempo slider to be freely movable if there is no Tempo text and the "Use jack transport" preference is disabled.

I can try building the master branch since my build system works and report back.

Reported version 3.5 3.2

That means the first version it was reported in was 3.2. This may help someone find where the code was written wrong.

In reply to by lazzarello

Built the 3.6alpha branch but not master because the complexity with QT 5.15 installation. The problem persists. To make it extra frustrating, the Tempo text BPM value in MuseScore will be overridden by jack transport but only when the transport is in play mode but that will not play the score. To play the score, the user must also click play in MuseScore. Stopping the jack transport also does not stop MuseScore from playing but the tempo setting persists.