Fixing slightly wrong aspect ratios

I keep getting frustrated by the fact that many models and application platforms do not strictly respect 16:9 aspect ratios.

This is a problem because if you want to export your final cut in a true 16:9 and the source video in not exactly 16:9 you will get small but annoying black bars on two edges. At least this is the case in my film editor, Filmora.

It's even worse if you are joining several videos which have different aspect ratios, because then you get shifting bars which are terribly distracting and ugly.

Probably those of you who are experienced already know how to fix this. But for newbies who may be struggling, I decided to write up this simple guide.

The first rule is that you always want to EXPAND the 'too-short' direction rather than shrink the 'too-long' direction. This avoids problems with your post-processing software possibly getting confused.

The first step is to divide the number of horizontal pixels by the number of vertical pixels. This ratio should be 16/9=1.777777...

If the ratio is less than this, the frame is too narrow and it must be expanded horizontally.

To do this, multiply the number of vertical pixels by 1.77777 to get the required number of horizontal pixels.

Divide the just-computed required size by the current size and multiply by 100 to get the percent horizontal scaling to enter into your production software.

If the ratio exceeds 1.777777 the image is too short and must be expanded vertically using the same basic idea.

For example, suppose the image produced by the model is 2144 (horz) by 1216 (vert), The ratio is 2144/1216=1.763. It's too narrow.

The required number of horizontal pixels is 1216 * 1.77777 = 2162.

The horizontal expansion factor is 2162/2144*100 = 100.84 percent.

On the other hand, suppose the model's image is 1928 by 1072. The ratio is 1928/1072=1.7985. It's too short.

The required height is 1928/1.77777=1084.

The vertical expansion factor is 1084/1072=101.12.

If you want slightly greater accuracy in the calculations, use the exact ratio 16/9 instead of 1.77777, and carry out all calculations to the full calculator precision rather than rounding.

The increased precision is negligible in most cases.

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