Created attachment 360070 [details]
modified iOS tutorial 4 that shows the issue

On iOS a pipeline such this one:

souphttpsrc ! matroskademux ! queue ! vtdec ! glupload ! glcolorconvert ! glimagesink

works fine and the video is showed in the supplied CAEAGLLayer but if you set the pipeline to NULL and you create it again using the same CAEAGLLayer the pipeline run, you can hear audio but video is not refreshed, glimagesink logs shows that the video is sent to the CAEAGLLayer.

If you replace vtdec with avdec_h264 then all is fine and the CAEAGLLayer is reusable as expected. 

Seems something like a cleanup issue.

I can reproduce the issue using iOS tutorial 4 with small modifications. 

Please note that in the provided example you need to change this line 

g_object_set(self->pipeline, "uri", "http://192.168.1.50/test6.mkv", NULL);

to point to a reachable H.264 media