The players. Most players have difficulty understanding and adjusting to the 16:9 flag in your file, so they display as 4:3. Manually set them to 16:9 and it should be OK. Burn to a DVD-RW and test it on your settop box and TV.
But Youtube specifically states it is configured for 16:9
And I should add that I was incorrect about my youtube videos, they do have black pillars on either side of the content AND the vertical aspect is stretched about 25%. I am uploading the original avi output files from Premiere Pro.
My flash videos and videos played back in Windows Media Player do not have the pillars, but they are stretched vertically. I have not attempted to playback on a TV or other device, as that it not my primary target.
What were you export settings? In detail, please. The problem is we can't see what you did, we can only read about it here. Screenshots would be helpful.
Are there details about my export settings that I neglected to mention above? I am not using the built in Adobe Media Encoder to output, I am simply choosing the "Movie" option under Export since .avi format works fine for me. Is that the problem?