Compression and ratio's

[Maxpower76]

Now I've heard and this may be very wrong. When you compress video footage in ratio's like 25%, 50% and 75% of the original, the quality is better than if you compress to say 67% of 44%. So if my HD footage at a width of 1920, it would look better at half the size at 960, then if it was say 730.

I hope that makes sense, and like I said, I may be wrong. But even in final cut the footage is better quality at 50% or 75% in the viewer...

 

[William_Robinette]

I would assume that halving or quartering the footage is similar math for the encoder to do and therefore offering a better result.

 

[milksac]

From my understanding the frame dimensions should be divisible by 16, 8 or 4. This has to do with the way video is compressed - blocks of 8 x 8 pixels. In your ratio examples using percentages the 50% size (960 x 540) would be fine, however the 25% (480 x 270) and the 75% size (1440 x 810) don't evenly divide into 16, 8 or 4.

That's as far as I'll go because that's about as much as I understand. At this point someone with a firm understanding of compression algorithms can chime in and give the details of the math.