Letterboxes on side of video

[billyb14]

I believe these are called pillarboxes and I don't know why they are appearing: http://farm3.static.flickr.com/2712/4149683187_afafd47edc.jpg

This is the preview of my video in the JW player's setup wizard. Here are the steps I took:
1. Recorded the video in HD (1080) and exported it in iMovie 09' at 1280x720 in a .mov format
2. Encoded the video using ffmegx at 1280x720 using the .264 codec.
3. I will be using the video on the web, so I set the size in the setup wizard to 512x288 so it will fit.
4. I got the result you see in the picture with the pillarboxes.

It looks like my video is in standard format, but I encoded it in HD and even the ffmegx preview on my computer showed it in HD. Is there an option I missed? Even using standard definition dimensions on the wizard leaves narrow pillarboxes.

This is the my fist time posting a movie on the web so any help with this or feedback about my general approach would be greatly appreciated.

[Baldrick]

Have you tried change the jw player settings? Like try set the stretching=fill.

[billyb14]

That did it, thanks Baldrick!

While I have your attention, do you think I should be encoding from ffmegx at the size I will be using on the web, or do this in the JW player settings? Or does it matter?

[Case]

For sharp/crisp playback, the .flv video size should match the size of the player window: both should be specified as 512x288, if that's the size you want.
Not specifying the movie dimensions to the player might be the cause that it defaults to aspect ratio 4:3. Or maybe your file lacks meta-data. Like what flvtool2 adds to an .flv file.

[billyb14]

Yes that looks better when I export at 512x288. Plus it turns out the JW player can now play .264 .mov files so I don't even need to convert to flash. Thanks Case.