Created attachment 132153 [details] Backtrace of the crash (all threads, very mildly redacted to protect the innocent) SUMMARY A custom business application I am working on sometimes crashes (segfaults) on exit with a backtrace that points at an issue within Phonon. While the application does not crash in a reproducible fashion, the backtraces appear quite similar to those reported in bug #321531 and friends where Digikam was crashing when it attemped to play back AVI media. The application in question runs on CentOS 7.7.1908 (x86-64) using Phonon 4.6.0, Phonon-GStreamer 4.6.3, and Qt 4.8.7. An all-threads backtrace, taken from a coredump, is attached. If you want further symbol information than what's provided, I can install more symbols and reinvestigate the coredump; if you want any other information, just ask here in a comment.
My investigation of the issue pointed me at a bad metaObject within the devnull NoDebugStream (derived from QIODevice). Following that trail to gstreamer/debug_p.h led me to notice that the Q_OBJECT macro in NoDebugStream's definition is commented out (in master, even!), which looks wrong since QIODevice is a QObject in the normal case (the only way it isn't is if QT_NO_QOBJECT is defined when qiodevice.h is #included). Is there a good reason for NoDebugStream to be defined the way it is, or am I onto something here? (NB: https://marcmutz.wordpress.com/effective-qt/subclassing/ seems to agree with what I am seeing that Q_OBJECT should have been there all along...)
A bit of a clarification on the investigation -- the bogus metaObject I mentioned stems from the QObject::d pointer within devnull being nullptr (zero-initialized, most likely).
Qt4 is long unmaintained.