Please describe the problem:
When linked to videoscale, modifying the keep-aspect-ratio property of ximagesink have an effect only once.
If you start a pipeline with the keep-aspect-ratio set once for all, it will always work fine. However, if you modify this property when playing, it will not work anymore.


Steps to reproduce:
1. start a pipeline with videoscale linked to ximagesink, keep-aspect-ratio=true
2. when playing, set keep-aspect-ratio to false, the video is enlarged to the window size
3. set keep-aspect-ratio to true


Actual results:
The video cannot be resized, the ratio cannot be preserved anymore.

Expected results:
The video should be resized to keep the aspect ratio as requested

Does this happen every time?
Yes

Other information:
Looking to the code, its seems that after the size has been negociated with the videoscale element, the src size equals the dst size(keep-aspect-ratio=false). Hence gst_video_sink_center_rect always gives the same result whatever the keep-aspect-ratio value.