gst-rtsp-server: Decrease RTSP setup time
Problem:
Setting suspend mode RESET on an RTSP media brings the live pipeline to NULL state on suspend.
When a PLAY request arrives, the pipeline is unsuspended and set to the PLAYING state. The source element has to release and reopen stream
resources and this operation, on our case, is time consuming due to device resource limits.
Solution:
Introduce a new suspend mode, that doesn't change the state of the media on suspend, meaning that the media is still PLAYING but remains blocked. When the media is unsuspended, the GstForceKeyUnit event is sent to the pipeline and the pipeline is flushed. The new generated key frame will unblock the media.
The patch will be provided.