Video
Non-square Pixels - 4
Images
Any image you import into your video will use square pixels. If it is mapped or scaled into the video frame based purely on pixel numbers, it will end up distorted when viewed on a TV. You have to compensate by effectively distorting the image's aspect to match that of the video frame. Exactly how you do this depends on the editor you use, but provided you understand what is going on it's not too difficult to work out.
Essentially, when using 576 line frames you must make the image narrower by 11/12 or taller by 12/11; when working with 480 line frames make the image wider by 11/10 or shorter by 10/11.
Some editors will re-scale an image to fit the video frame if no special positioning is required, regardless of the image's original proportions. If you make sure you start with images that have a 4:3 aspect ratio then this technique saves you having to work out any adjustments. If you want to compensate exactly for DV's extra pixels your images actually need to have an aspect ratio of 15:11, but you may choose to ignore this minor error for the sake of simplicity.
Circles and squares
If you apply an effect that involves a circle - a contracting-circle transition for example - the editor will calculate the circle on the assumption that the pixels are square. On a TV the circle will be slightly oval. This may not be a problem, and you may not even be able to adjust the transition to compensate, but you should be aware of the result. It's worth viewing a test of the effect on a TV to see if it's acceptable, if not you might prefer to choose to use a different effect.
The same argument applies to squares, but human vision can detect small deviations from an exact circle much more easily than it can detect deviations from an exact square.
Frame rotation
If you use an effect involving a rotating frame, such as a moving image-in-picture, you can get a similar problem. You may start with your moving image positioned horizontally, with the height and width adjusted to compensate for the video frame's pixel aspect. If you then set it to rotate, the editor will keep the pixel size constant, but once it has turned 90 degrees your original compensation is completely wrong. At this point it should be compensated the opposite way.
If you can add check points to your moving path control, you should put one at each point where the inserted image is aligned horizontally and vertically. You should then adjust the aspect ratio of the inserted image according to its orientation.
You could alternatively not apply any compensation on the basis that on average the aspect ratio is right and the changes as it rotates won't be noticed, which is the more pragmatic solution!
If you put a rotating video-in-picture the process is slightly different. When horizontal no correction is needed because the inserted image has the same pixel aspect ratio as the main image. But when turned 90 degrees it needs double the correction factor applying if the proportions are to remain correct. You may again decide its not noticeable, or even decide you like the effect! Nevertheless it helps to understand what's going on.
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