MelodyBomber
VRChat crashes of an AVPro video player opening any
TopazChat live stream (rtspt protocol, host topaz.chat). Four crashes in one
evening, three different broadcasters' streams, so not specific to one stream.
Crash signature, byte-identical across all four crashes:
Faulting module: msmpeg2vdec.dll (Windows H.264 decoder), version 10.0.26100.8758
Exception: 0xc0000005, read of address 0x1348
Fault offset: 0x2f848
WinDbg on the minidump shows a NULL-pointer dereference on a decoder-owned
worker thread. All stack frames are inside msmpeg2vdec.dll, with no VRChat,
AVPro, or GPU driver frames. Timing suggests a race during stream startup.
Important: the launch option disable-hw-video-decoding does NOT help. Logs
confirm the playback path switched from MF-MediaEngine-Hardware to
MF-MediaEngine-Software and the crash still occurs at the same offset, since
msmpeg2vdec.dll is the CPU bitstream decoder used by both paths. GPU and
driver are ruled out.
Repro: join any world with a TopazChat player and play a live stream.
Crash will happen when trying to load that stream.
Environment: Windows 11 Pro for Workstations 26H2, build 26300.8758.
VRChat PC (Steam), Build 1865. Tested on Unity 6 Public Beta,crashes too.
Root cause is in Microsoft's code and I have filed a Feedback Hub report as
well, but VRChat may be able to work around it client-side, and your crash
telemetry should show this bucket for any user on current Windows builds.
Full WER minidumps (about 75 MB each, four crashes) available on request.