On OS X 10.9 with gst-plugins-bad built from cerbero from 967982a0b5362d500081d3353667e089b996641b , if I try to run the following pipeline, I observe a segfault:

gst-launch-1.0 mix. ! queue ! glimagesink \
    gltestsrc pattern=black ! video/x-raw,width=1280,height=800 ! queue name=background \
    avfvideosrc device-index=0 ! video/x-raw,width=1280,height=720 ! glcolorscale ! video/x-raw,width=640,height=720 ! queue name=left \
    avfvideosrc device-index=0 ! video/x-raw,width=1280,height=720 ! glcolorscale ! video/x-raw,width=640,height=720 ! queue name=right \
    background. ! mix.sink_0 \
    left. ! mix.sink_1 \
    right. ! mix.sink_2 glvideomixer name=mix sink_2::xpos=640


Output and backtrace:

Current executable set to 'gst-launch-1.0' (x86_64).
(lldb) r
Process 90503 launched: '/path/to/bin/gst-launch-1.0' (x86_64)
Setting pipeline to PAUSED ...
Pipeline is live and does not need PREROLL ...
Got context from element 'glimagesink0': gst.gl.GLDisplay=context, gst.gl.GLDisplay=(GstGLDisplay)NULL;
Setting pipeline to PLAYING ...
New clock: GstSystemClock

(gst-launch-1.0:90503): GStreamer-CRITICAL **: guint64 _gst_util_uint64_scale_int(guint64, gint, gint, gint): assertion 'denom > 0' failed

(gst-launch-1.0:90503): GStreamer-CRITICAL **: guint64 _gst_util_uint64_scale_int(guint64, gint, gint, gint): assertion 'denom > 0' failed
Process 90503 stopped
* thread #17: tid = 0x10e53b, 0x0000000101812e93 libgstopengl.so`gst_gl_video_mixer_callback(stuff=<unavailable>) + 1091 at gstglvideomixer.c:243, stop reason = EXC_BAD_ACCESS (code=1, address=0x220)
    frame #0: 0x0000000101812e93 libgstopengl.so`gst_gl_video_mixer_callback(stuff=<unavailable>) + 1091 at gstglvideomixer.c:243
   240 	      count++;
   241 	      continue;
   242 	    }
-> 243 	    in_width = GST_VIDEO_INFO_WIDTH (&frame->pad->in_info);
   244 	    in_height = GST_VIDEO_INFO_HEIGHT (&frame->pad->in_info);
   245 	
   246 	    if (!frame->texture || in_width <= 0 || in_height <= 0) {


(lldb) bt
* thread #17: tid = 0x10e53b, 0x0000000101812e93 libgstopengl.so`gst_gl_video_mixer_callback(stuff=<unavailable>) + 1091 at gstglvideomixer.c:243, stop reason = EXC_BAD_ACCESS (code=1, address=0x220)
  * frame #0: 0x0000000101812e93 libgstopengl.so`gst_gl_video_mixer_callback(stuff=<unavailable>) + 1091 at gstglvideomixer.c:243
    frame #1: 0x000000010185fadf libgstgl-1.0.0.dylib`gst_gl_framebuffer_use_v2(frame=<unavailable>, texture_fbo_width=1280, texture_fbo_height=800, fbo=8, depth_buffer=<unavailable>, texture_fbo=19, cb=<unavailable>, stuff=<unavailable>) + 287 at gstglframebuffer.c:307
    frame #2: 0x000000010185e816 libgstgl-1.0.0.dylib`_use_fbo_v2(context=<unavailable>, data=<unavailable>) + 54 at gstglutils.c:419
    frame #3: 0x000000010185d12d libgstgl-1.0.0.dylib`_run_message_sync(message=0x0000000103f44568) + 29 at gstglwindow.c:341
    frame #4: 0x00007fff9164613e Foundation`__NSThreadPerformPerform + 229
    frame #5: 0x00007fff86dfa661 CoreFoundation`__CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 17
    frame #6: 0x00007fff86debd12 CoreFoundation`__CFRunLoopDoSources0 + 242
    frame #7: 0x00007fff86deb49f CoreFoundation`__CFRunLoopRun + 831
    frame #8: 0x00007fff86deaf25 CoreFoundation`CFRunLoopRunSpecific + 309
    frame #9: 0x00007fff9164badc Foundation`-[NSRunLoop(NSRunLoop) runMode:beforeDate:] + 253
    frame #10: 0x0000000101861190 libgstgl-1.0.0.dylib`gst_gl_window_cocoa_run(window=<unavailable>) + 240 at gstglwindow_cocoa.m:283
    frame #11: 0x0000000101845df4 libgstgl-1.0.0.dylib`gst_gl_context_create_thread(context=0x0000000103009be0) + 2580 at gstglcontext.c:843
    frame #12: 0x0000000100235e8a libglib-2.0.0.dylib`g_thread_proxy(data=0x000000010200b050) + 90 at gthread.c:798
    frame #13: 0x00007fff8cf46899 libsystem_pthread.dylib`_pthread_body + 138
    frame #14: 0x00007fff8cf4672a libsystem_pthread.dylib`_pthread_start + 137