[Bug 740671] aspectratiocrop: crop needs to be reset when video size changes

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=740671
  GStreamer | gst-plugins-good | git

--- Comment #21 from Andrei Sarakeev <sarakusha at gmail.com> 2014-11-27 05:56:31 UTC ---
example continuous playback:
first video - 1280x720
second video - 320x240
aspect ratio - 4:3
pipeline:
source/playbin -> aspectratio (videocrop) -> xvimagesink

1. first video, source send caps-event1(width=1280,height=720)
2. aspectratio receive caps-event1
3. -- aspectratio send caps-event1 downstream
4. -- videocrop (crop t=0,b=0,l=0,r=0) send caps-event1 downstream
5. -- xvimagesink receive caps-event1, set output window size *1280x720*!!!
6. aspectratio set new crop (t=0,b=0,l=160,r=160)
7. videocrop (t=0,b=0,l=160,r=160)
8. playing...

9.  second video, source send caps-event2 (width=320, height=240)
10. aspectratio receive caps-event2
11. -- aspectratio send caps-event2 downstream
12. -- videocrop (crop t=0,b=0,l=160,r=160) changed caps-event2 to caps-event3
(width=320 - l - r, height=240 - t - b)=>(width:0, height:240)
13. -- xvimagesink receive caps-event3 (width=0,height=240) and throw
error-message
14. aspectratio set new crop (t=0, b=0, r=0, l=0) too late

if we switch the step 3 and 6, 11<->14 then videocrop get the freshest
information on time, then:
8. xvimagesink receive caps-event (width=960,height=720)
and
13. xvimagesink receive caps-event (width=320, height=240)

I have bad speaking skills, change the commit message itself

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