Latency time too high on video play when DV cam is used

[NicoInattendu]

When acquiring from a DV cam , the time to have the video back on screen after each snapshot.
This latency time goes increasing after each snapshot, until no more dv cam display.

[NicoInattendu (nico-inattendu)]

Problem is confirmed, and due to a wrong usage of gstreamer.
When a snapshot action is done , the video stream is stopped , i.e. Gststate goes to STATE_NULL, and then the restart of video is incorrect, a WARN is raised : "pipeline gstpipeline.c:491:gst_pipeline_change_state:<pipeline0> failed to query pipeline latency "

This phenoma doest not appears when onion skin is activated, the reason is in that case the gst pipeline is reseted before going in play state.

2 solutions possible ( workarounds ?) :
- reset the pipeline after each snapshot.
- go in pause mode , instead of "STOP", with that solution, the time for making ths snapshot is shorter.

[NicoInattendu (nico-inattendu)]

The solution chosen is to go in pause mode. This solution is experimental.
Some robustness effort is also needed module myrtille_acquisition and myrtille_class , to avoid unexpected crash of gstreamer or IOerror.

[NicoInattendu (nico-inattendu)]

Solution to be checked , now acquisition is quicker , check robustness effort