Further information - when I'd render an .avi video captured from a camcorder tape I always used the H.264/AVC when selecting under the Export window. As it rendered the video maintained it's Display Aspect Ratio of 4:3 (in a widescreen format...yes - black bars down either side) but when played back on ANY device the Display Aspect Ratio had changed to 3:2 when looking at the file using MediaInfo. So I'd re-render the video using the MPEG-4 Visual option from the Format option pull-down menu and lo & behold, the rendered video, when looked at using MediaInfo showed the Display Aspect Ratio as 16:9 Widescreen and all the proportions were accurately displayed - no longer narrow. BUT IT ISN'T USING THE H264 Codec - it's using the mp4v-20.
On the Pinnacle 21U pc, the same video renders out properly using the H.264/AVC from the drop down and the codec used is the H264 - which is the most common codec out there I believe in SmartTV's.