Pushes a buffer to the peer of pad.
This function will call installed block probes before triggering any
installed data probes.
The function proceeds calling Pad.chain on the peer pad and returns
the value from that function. If pad has no peer, GST_FLOW_NOT_LINKED will
In all cases, success or failure, the caller loses its reference to buffer
after calling this function.
the gstreamer.Buffer to push returns GST_FLOW_ERROR
a GstFlowReturn from the peer pad.