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Qtractor Qt5 vs Qt4 plugins

Qtractor git now builds against Qt5 by default. The outcome of this is that Qtractor segfaults when it scans for plugins if you have any Qt4 plugins installed.

In my case I had to uninstall Carla before I could insert any plugins into Qt5 Qtractor. I have not yet checked if I can re-build Carla against Qt5 now but I'd imagine falkTX will be working on Qt5 support if it doesn't support Qt5 already.

Here is crappy shell script that might help others find out what plugins they have installed that Qtr Qt5 won't like. Run it as-is first then run it again substituting /usr/lib/lv2 for /usr/lib/vst and so on for any other dirs you have that contain Linux audio plugins:

for p in $(find /usr/lib/lv2 -name "*.so");
 echo "Checking $p for Qt4 dependency"
 ldd "$p" | grep

Might there be a better way than using my excuse for a script Rui?

rncbc's picture

thanks for the fish, erm.... the script!

you still have to poke falktx to hurry and migrate to qt5 asap; most distros are already posed to qt5 and leave qt4 behind.
also as stated on this late "meson dope" announcement, the next qtractor release will default to qt5--no excuses!
however, ppl will still have the --enable-qt4 configure option available, nevertheless.


I've just consulted Mr TX and apparently Carla VST only works with Qt4 ATM although regular Carla does support Qt5.

rncbc's picture

to avoid the crash during VST scan you can revert to the infamous dummy-VST scan... that way it won't actually load any VST(.so) plugins during scan but it will crash if you insist to select and open any that is based on qt4 though;

one side-effect of the so called "dummy-VST scan" is that it won't show any VST-shell sub-plugins for selection thereafter; however you can still work with any previously saved sessions that include any of those.

also note that eventually, if you still run older qtractor-qt4 in presence of newer qt5-plugins, the same crash-issue applies as in a vice-versa scenario.


Sorry for beating this dead (or at least old) horse some more. But I'm also bitten by this segfault, *in spite* of having the dummy VST scan enabled in the Qtractor preferences. As the Carla LV2 plugins just work fine in Qtractor, it's a nuisance having to manually get rid of the Carla VSTs in some way just so that Qtractor doesn't fall apart at their scary Qt4ish looks. ;-)

No seriously, Rui, it would be nice to have a way to blacklist plugins in some way, so that Qtractor completely ignores them. Might even be a text file hidden away in some very dark corner of ~/.config. ;-)

rncbc's picture

following falktx call and if it's only carla.vst that is in the way, it will suffice to remove the "styles" symlink under "/usr[/local]/lib/vst/carla.vst/"

after that move you're back in the game with qtractor-qt5 !

a blacklist won't do any good, unless you know the exact primary to each blacklist entry in advance, just because the qt4 vs qt5 crash happens upon dlopen() and not due to some dynamic call afterwards, for which one could detect whether being linked to "" (qt4) or "" (qt5), and never ever have both loaded on same process address-space.


Thought you might appreciate some stinky script RNCBC!

Looks like F is in trouble!


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