Video thumbnails are now generated from the frame whose timepoint is 1/3 of the video's duration. This eliminates a problem where many video thumbnails would appear black because of fade-in effects. Closes #2568.
Video thumbnails are now generated from the frame whose timepoint is 1/3 of the video's duration. This eliminates a problem where many video thumbnails would appear black because of fade-in effects. Closes #2568.


jof/shotwell,Sanva/shotwell-gsoc,h4ck3rm1k3/shotwell,h4ck3rm1k3/shotwell,Sanva/shotwell-gsoc,jimbonator/shotwell,abrauchli/shotwell,damianmoore/shotwell,Sanva/shotwell-gsoc,abrauchli/shotwell,polymeris/shotwell,jof/shotwell,jimbonator/shotwell,damianmoore/shotwell,polymeris/shotwell,ritchiewilson/shotwell,polymeris/shotwell,damianmoore/shotwell,jof/shotwell,ritchiewilson/shotwell,jimbonator/shotwell,ritchiewilson/shotwell,h4ck3rm1k3/shotwell,abrauchli/shotwell