Widescreen SD is an "anamorphic" format. This means that the PAR (pixel aspect ratio) is different to give the appearance of widescreen, even though the frame dimensions are the same. NTSC DV uses 720x480 for both 4:3 and 16:9, with PARs of 0.9 and 1.2 respectively. The rectangular pixels of widescreen DV with 1.2 PAR provide the widescreen image look.
Some software players do not look at the PAR and assume a 1.0 PAR (square pixels) and that is why your video is displayed as 4:3.
If creating a video for online display, you may have to correct using pixels, which means export at 854x480 using a 1.0 PAR and then it will always look like 16:9 when viewed. For PAL, I believe 1024x576 is correct for 1.0 PAR, not certain though.
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