kenrivers :
Have you tried rendering the file again and uploading it to YouTube? If yes, did the video still have the black (letterboxing) bars? Upscaling SD video to HD video, even 720p, can be a bit tricky since SD video lacks the information of HD video.
I uploaded a second video last night only rendered with the Internet HD 720p settings. The black bars are still there. If it helps, I was using a custom template based off of the Internet HD 720p settings. I have sampling disabled and maintain aspect ratio disabled as well. When aspect ratio is checked, it leaves the black bars on the side of the video rather than on top. This is twice as annoying.
These are the settings I am currently using for my videos (click to expand):
Main video clip properties:
Main project properties:
Internet HD 720p Custom Template video settings:
Internet HD 720p Custom Template project settings:
The video quality is great, full HD. The video will maintain the proper size until you try to expand to full screen mode, that's when the black bars appear.
I appreciate the help and I hope my images can give you an idea of what my settings are configured for... please ask any questions if you have them.