Here's my situation. I have video that was shot in 16x9 SD on a Panasonic DVCPRO camera. However, the editing system at my station (an old version of Media 100 v8.2) can't edit 16x9 properly; at least in my opinion. When I capture it, it's noticeable that the video was shot widescreen because everything is squished. All of out external monitoring is done in 4x3. But when the Media 100 outputs the video, it doesn't output it in letterbox format so it's shown correctly on my 4x3 monitor. And when it's output to tape, again, it's not in letterbox format. I can do manual resizing of the clip in Boris to add the black bars at the top and bottom so it looks correct. But what I want to know is how big should those bars be and what percentage of the screen should they take up? And is there a setting in the Media 100 that I can change to do this automatically so that I see it in widescreen letterbox format on my monitor? Whether I use a 4x3 project or 16x9 project makes no difference, I've tried both with the same results.
What you are seeing and working with is 16:9 anamorphotic video, meaning that it is in the normal 720*576 (PAL) or 720*486 (NTSC) size, but the pixels should get displayed in a much more rectangular way than with 4:3 video. When you set Media 100 i to 16:9, you will see that your viewer windows are changed to 16:9 aspect ratio, and your video is displayed correctly on your computer screen (if your footage is not acquired as 16:9 you can change that via the "Change Media attributes" command, which only will change the "flagging" of the video to tell the system that it is widescreen footage.
You need to change the settings on your video monitor to 16:9 to view anamorphic footage correctly. And make sure to label your tapes correctly, so that the person receiving the tapes will know that it is 16:9.
What you are speaking about with the black bars is not 16:9, but is a 4:3 letterboxed version of your 16:9 footage, which will lose picture informations. Media 100 i cannot output a letterboxed version in realtime (Media 100 HD on the Kona3 board can). If you want to resize it in Boris to a 4:3 letterbox version you need to scale it to 75% on the Y axis.