Due to the possibility to connect to two or more streams simultaneously with different clocks synchronization It's necessary to improve the timestamps calculation to detect this.
Prior to this commit, we saved the first timestamp that arrive and use it to calculate the running time of the stream for the rest of frames (pts field in gstreamer buffer) in all of the streams. This lead to problems when connecting to multiple streams in multiple computers and the clocks were not correctly synchronized.
To fix this, now we save a different initial timestamp for each stream.
We could also go via the glib::Type but that requires more steps unless
we also add a getter from the registered type to the audio/video source
modules.
