How to set V4l2 control values while a Gstreamer pipeline is active in C

I am developing an application in Qt which is using gstreamer to stream image from a webcamera.I am unable to change the default v4l2 controls of the camera.Whenever i am trying to set controls while gstreamer pipeline is run my program is crashing.

Dump o开发者_Go百科f assembler code for function __kernel_vsyscall: 0x0012d420 <+0>: int $0x80 0x0012d422 <+2>: ret End of assembler dump.

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Before change any property of any element, you have to set your pipeline state to paused state, or stopped state, and resume the streaming (by setting the pipeline to playing state) after the properties have been changed successfully.

Here is a link about dynamically changing a pipeline.

best regards