videorate: Should be able to duplicate frames in a live stream

Submitted by Frédéric Sallé

Link to original bug (#720104)

Description

Currently the videorate component insert a set of duplicated frames only at the reception of a new buffer with timestamps in the past for that new frames.

If you requested a framerate of 20fps and that your input stream is let say 1 fps, each time videorate receive 1 frame, it send a burst 19 duplication of the previous frame with proper timestamps over the last second.

If this behaviour is quite ok with non live streams, for live streams this create a lag in your pipeline.
For live streams, you expect that a new frame is inserted every 50 ms (for a target of 20fps).