Crash on launch on Linux starting with 26.6

[gavgav11]

• Operating System: Linux
• Shotcut Version: 26.6.25, 26.8.1

Describe the bug
Shotcut crashes on launch. The window appears for a split second then disappears. This happens twice per launch as if the app reattempts to start.
App was compiled from source, tried compiling with make and ninja with same result.
cmake -DCMAKE_INSTALL_PREFIX=/opt/shotcut -DCMAKE_BUILD_TYPE=Release -GNinja ..

Is there a log file that can be checked for more info? Output is

No appenders associated with category qt.qpa.services
[Warning] <> Failed to register with host portal QDBusError("org.freedesktop.DBus.Error.ServiceUnknown", "The name org.freedesktop.portal.Desktop was not provided by any .service files")
libDeckLinkAPI.so: cannot open shared object file: No such file or directory
---
formats:
***long list***
...
---
audio_codecs:
***long list***
...
---
video_codecs:
***long list***

[Info   ] <> Using Qt multimedia with FFmpeg version 7.1.5 nonfree and unredistributable
libva info: VA-API version 1.23.0
libva info: Trying to open /usr/X11/lib/dri/radeonsi_drv_video.so
libva info: Found init function __vaDriverInit_1_23
libva info: va_openDriver() returns 0

Steps To Reproduce

1. Start Shotcut
2. Crash

[ddennedy]

Forget about making your own build first; I do not help people with that. Which Linux distro and how did you install it? Try with a build we provide, and say which app formats you tried.

[gavgav11]

I'm using LFS. Not asking for build help, just need to know where to look for the error because the console output does not help in troubleshooting.

[ddennedy]

When a binary crashes, it does not show anything on the console; it exits immediately. You need to use a debugger (e.g. gdb) to see where it crashed. There are hundreds of indirect dependencies and could crash anywhere in them as well as Shotcut. You should verify your MLT install using the melt command line utility to play some video file.

[gavgav11]

I tried that, it seems to be exiting. No backtrace.
[Thread 0x7fffe3afd6c0 (LWP 1844) exited]
[Thread 0x7fffe42fe6c0 (LWP 1842) exited]
[Inferior 1 (process 1839) exited normally]

Melt works with audio/video.

[ddennedy]

Oh, sorry forgot to mention. Shotcut now runs a parent watchdog process to restart in a safe mode (no external plugins) if there is a crash on startup. Disable that with the environment variable SHOTCUT_WATCHDOG=1 and then use gdb.

[gavgav11]

Ok, now I got the backtrace. Qt version is 6.11. Not sure what it wants, any guess would be appreciated.

Thread 1 "shotcut" received signal SIGSEGV, Segmentation fault.
0x00007ffff5c209d4 in QRhiGles2::setGraphicsPipeline(QRhiCommandBuffer*, QRhiGraphicsPipeline*) () from /opt/qt6/lib/libQt6Gui.so.6
(gdb) backtrace 
#0  0x00007ffff5c209d4 in QRhiGles2::setGraphicsPipeline(QRhiCommandBuffer*, QRhiGraphicsPipeline*) () at /opt/qt6/lib/libQt6Gui.so.6
#1  0x00007ffff58859b4 in QBackingStoreDefaultCompositor::flush(QPlatformBackingStore*, QRhi*, QRhiSwapChain*, QWindow*, double, QRegion const&, QPoint const&, QPlatformTextureList*, bool, double) () at /opt/qt6/lib/libQt6Gui.so.6
#2  0x00007ffff5a30bc4 in QPlatformBackingStore::rhiFlush(QWindow*, double, QRegion const&, QPoint const&, QPlatformTextureList*, bool, double) ()
    at /opt/qt6/lib/libQt6Gui.so.6
#3  0x00007fffe436e38a in QXcbBackingStore::rhiFlush(QWindow*, double, QRegion const&, QPoint const&, QPlatformTextureList*, bool, double) ()
    at /opt/qt6/lib/libQt6XcbQpa.so.6
#4  0x00007ffff73fe8fd in QWidgetRepaintManager::flush(QWidget*, QRegion const&, QPlatformTextureList*) () at /opt/qt6/lib/libQt6Widgets.so.6
#5  0x00007ffff73ffeb4 in QWidgetRepaintManager::flush() () at /opt/qt6/lib/libQt6Widgets.so.6
#6  0x00007ffff7402043 in QWidgetRepaintManager::paintAndFlush() () at /opt/qt6/lib/libQt6Widgets.so.6
#7  0x00007ffff740300a in QWidgetRepaintManager::sync(QWidget*, QRegion const&) () at /opt/qt6/lib/libQt6Widgets.so.6
#8  0x00007ffff740d090 in QWidgetWindow::event(QEvent*) () at /opt/qt6/lib/libQt6Widgets.so.6
#9  0x00007ffff738ca78 in QApplicationPrivate::notify_helper(QObject*, QEvent*) () at /opt/qt6/lib/libQt6Widgets.so.6
#10 0x00007ffff43a72f8 in QCoreApplication::notifyInternal2(QObject*, QEvent*) () at /opt/qt6/lib/libQt6Core.so.6
#11 0x00007ffff57f990f in QGuiApplicationPrivate::processExposeEvent(QWindowSystemInterfacePrivate::ExposeEvent*) () at /opt/qt6/lib/libQt6Gui.so.6
#12 0x00007ffff586484b in QWindowSystemInterface::sendWindowSystemEvents(QFlags<QEventLoop::ProcessEventsFlag>) () at /opt/qt6/lib/libQt6Gui.so.6
#13 0x00007fffe439987e in xcbSourceDispatch(_GSource*, int (*)(void*), void*) () at /opt/qt6/lib/libQt6XcbQpa.so.6
#14 0x00007ffff41017c4 in g_main_dispatch () at /usr/lib/libglib-2.0.so.0
#15 0x00007ffff4104ab8 in g_main_context_iterate_unlocked.isra () at /usr/lib/libglib-2.0.so.0
#16 0x00007ffff410528c in g_main_context_iteration () at /usr/lib/libglib-2.0.so.0
#17 0x00007ffff46e4258 in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () at /opt/qt6/lib/libQt6Core.so.6

[ddennedy]

If you have vulkan on your system, you can try running with environment variable QSG_RHI_BACKEND=vulkan.

[gavgav11]

Massive thanks! That worked!

[ddennedy]

Great! Now, change Settings > Display Method to Vulkan and you can try starting without any extra environment variables.

[gavgav11]

I see, thanks again!

[ddennedy]

For readers who get here and do not want to use an environment variable, you can edit ~/.config/Meltytech/Shotcut.conf and change or set the line opengl=5 under the [General] section.