Blender VSE tip : Fixing aspect ratios for larger than stage images and footage.

Blender's VSE is really good considering its free but it fails at some basics. Like why does not an image with a different aspect ratio when imported to stage maintain its aspect ratio?

Yes you can check "Image offset" and correct it but only on images that are smaller in both width and/or height of the stage. On a larger image or video you either get a stretched image or a cropped one and no you can't get the cropped areas back by scaling it down.

So we are left with two options. One is to use another program to scale the image or footage to fit the stage resolution and the other is to correct it with the "Transform" effect strip. We are going to do the latter.

Side note: Use the Transform Effect strip to resize only when re-sampling quality is not that important and you just want something done fast. Read about it here.

An example problem is, you have a digital cam image which is of resolution 3200x2400 (4:3 aspect ratio) and you want to import it to your 1920x1080 (16:9 aspect ratio) stage. This causes it to stretch sideways. So you add a transform effect strip and scale along X axis till it looks right. But is it accurate? If you scaled X by 0.75 then yes, it is correct! So how do we get 0.75?

These formulae...

If image is stretched horizontally then scale along X axis by 

(Width of Image * Height of stage) / (Height of Image * Width of stage)

or if the image is stretched vertically then scale along Y axis by 

(Height of Image * Width of stage) / (Width of Image * Height of stage)

Our example problem is horizontal stretch, so we take the first formula and get...

(3200*1080)/(2400*1920) = 0.75

and enter 0.75 into the X scale of the transform effect strip's properties.

If you know the aspect ratios of the image and stage, 4:3 and 16:9 in this case, you could instead do...

(4*9)/(3*16) = 0.75

Which is essentially the same thing and you don't have to type in four digit numbers.

As a picture for reference

Now only if there was an addon for this.

All it needs is one single button to check the nature of stretch, add transform effect and do the math for all selected strips. I don't know much about coding but this one if feel shouldn't be too hard. Would be superb to have it. Would come real handy when making slideshows out of photos and such where a lot of strips need to get processed.