Problem resizing videos

I’m having a problem resizing videos. I have a video that is 1280 x 720 and I want it to appear on the web page as 800 x 450. The largest dimension that I can get the player to resize to (even if I set it and the default video dimensions setting to 1280 x 720) is 720 x 412. At this size, the splash screen is 651 x 405, and the video itself is 591 x 366 (far from the 800 x 450 size that I want).

Rather than appearing with perhaps a small black letterbox or pillarbox margin at most, the video is also appearing with both of these which makes it unsightly. It was produced with a 16:9 aspect ratio (1280 x 720) and I want it to display in a 16:9 aspect ratio (800 x 450), so I don’t understand why it is being embedded with a different aspect ratio and these ugly margins.

I am using the FV Flowplayer plugin. I have deactivated all the plugins except Flowplayer and the problem still occurs. AND, this problem DID NOT occur when I embedded two other animations with Flowplayer that are also 1280 x 720, but do appear on the web page as 800 x 450 with only a slight letter OR pillar box margins, as I want them to. The only difference is that the video is much longer so I had to upload it to my host’s server via FTP, however I did transfer it to the WordPress media library where the dimensions are correctly indicated as 1280 x 720.

Any ideas how to fix this problem?

http://ww.wp.xz.cn/plugins/fv-wordpress-flowplayer/