"When I try and play this video, I see corruption on the edges of the video." Regressing determined that this was caused by http://trac.webkit.org/changeset/146531.
RenderVideo does not paint a background color if it has a poster attribute, breaking the assumptions of RenderLayer::backgroundIsKnownToBeOpaqueInRect().
But also RenderImage::backgroundIsKnown.... doesn't deal with aspect-ratio resize that RenderVideo does.
Created attachment 199872 [details] Patch
In a future patch, RenderImage should change it's implementation of foregroundIsKnownToBeOpaqueInRect() to take into account object-fit.
Comment on attachment 199872 [details] Patch Attachment 199872 [details] did not pass mac-wk2-ews (mac-wk2): Output: http://webkit-queues.appspot.com/results/58666 New failing tests: media/video-poster-background.html
Created attachment 199888 [details] Archive of layout-test-results from webkit-ews-16 for mac-mountainlion-wk2 The attached test failures were seen while running run-webkit-tests on the mac-wk2-ews. Bot: webkit-ews-16 Port: mac-mountainlion-wk2 Platform: Mac OS X 10.8.2
The new test is failing with a 0.01% image diff. The artifacts introduced by the .jpg version of the video frame are enough to trigger a image failure. I've updated the test to clip out the video frame, leaving only the video background visible. This eliminates the 0.01% image diff.
Committed r149232: <http://trac.webkit.org/changeset/149232>