I just found this page in the YouTube help section that details how to fix problems with your aspect ratio (if it looks stretched or squashed or there’s black area all around the video), just by adding some secret YouTube tags to your video:
- yt:crop=16:9 (zooms in on the 16:9 area, removes windowboxing)
- yt:stretch=16:9 (fixes anamorphic content by scaling to 16:9)
- yt:stretch=4:3 (fixes 720×480 content that is the wrong aspect ratio by scaling to 4:3)
- yt:quality=high (default to a high quality stream, depending on availability)
I rendered a video, and it seemed to have the wrong meta data encoded in it. It was 854×480 (480p widescreen), but for some reason Windows Media Player as well as YouTube both thought it was 864×480 (too wide). So I just added the “yt:stretch=16:9” tag to the video’s list of tags, and it displays perfectly.