[mythtv-users] Solution: frontend crash on playback

Doug Larrick doug at ties.org
Thu Dec 30 11:40:38 UTC 2004

mikemurphy wrote:
> Hey all,
> My appollogies if this has already been covered, but I just worked 
> around a nasty hangup and I'm pretty excited about it, so I thought I'd 
> share in case anyone else is where I was for about the last 4 days.
> Exactly the output in the post.  Apparently the problem is with OpenGL 
> vsync and NVidia drivers.
> Elsewhere in the thread someone mentioned that you can disable OpenGL 
> VSYNC in Myth by commenting out the OpenGL VSYNC block in the 
> settings.pro file in the Myth source directory and recompiling from scratch
> My Uneducated Theory:
> Backtrace on the same crash shows that it's crashing inside the OpenGL 
> library provided by NVidia

Yes.  What nVidia version are you running?  Anything prior to 6111 is 
known to cause this problem.

> Program received signal SIGSEGV, Segmentation fault.
> [Switching to Thread 196616 (LWP 1055)]
> 0xb64ec226 in _nv000833gl () from /usr/lib/libGLcore.so.1
> (gdb) bt
> #0 0xb64ec226 in _nv000833gl () from /usr/lib/libGLcore.so.1
> #1 0xb73d4210 in _nv000030gl () from /usr/lib/libGL.so.1
> #2 0x00030008 in ?? ()
> #3 0x0000041f in ?? ()
> #4 0xb7f2dda8 in ?? () from /usr/lib/libmythtv-0.16.so.0
> (gdb) kill
> If it's crashing because it can't open /dev/dri/card0, thien it makes 
> sense, because there's no such file in my /dev filesystem. 

No, the nVidia driver is not looking for /dev/dri/card0.  That's for the 
"DRI" vsync method (which fails, because your hardware doesn't support 
it).  /dev/nvidia0 (another vsync method, the vblank ioctl method 
message) *is* there, but also fails because your nVidia driver version 
is too new.  OpenGL is the first one that succeeded.

If you can get it to work, OpenGL will give better video smoothness than 
RTC (which you are probably using), or usleep w/ busy-wait (which also 
consumes more CPU).  As an exercise, see if you can spot the --verbose 
playback output that tells you which you're using, and if it's not RTC, 
search the list archives to see what to do about it.

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