Aspect ratio

[Rich Rubasch]

Since flass video will be viewed on a compute monitor (most likely) it should be viewed with square pixel dimensions. 720 x 480 DV video is non-square pixels. The square pixel equivalent would be 720 x 534.

By choosing “Maintain Aspect” the encoder believes you want to maintain the non-square pixel dimensions and scales down accordingly.

Using 720 x 534 as the square pixel equivalent to your source clip, you can multiply the dimensions by .75 to get in the ballpark to what you want the Flash video to be.

720 x .75 = 540
534 x .75 = 400.5 (round to 400)

If you want your horizontal frame to be 540 pixels, I would set the vertical size to 400 pixels (with “Maintain Aspect” not checked) and you will have a non distorted image in the final Flash clip.

Did this help?

Rich Rubasch
Tilt Media

[Eric Murty]

Thanks Rich for this detailed response. The problem is the layout that was given to me has to stay at 540 x 360. The strange thing is I’m not seeing distortion. By scaling it to 540 x 360 isn’t this still keeping the scale at a fixed proportion at least in Photoshop it is?

Thanks for your help.

[Eric Murty]

Ok so I did a test I compressed one video at 540 x 400 and the other at 540 x 360 both from the same source DVD 720 x 480. To my eye there is no difference between the 2. I see know distortion. If all my files are going to be 720 x 480 to start with can I get away with using 540 x 360 or do I have to stick with 540 x 400

Thanks,

[Craig Seeman]

Try 512×384 (ideal), 528×396, 544×408 if you can go over a bit (and maybe crop).

Rich pointed at one way to do the math. Here’s another:
720×480 non square is also 640×480 square pixels.
You can think of moving up or down frame size by 32×24.

Because of the way most codecs work when they encode in blocks, keeping things divisible by 16 evenly is a good rule. At the very least the number should be divisible by 4 or 8.

Here’s an example:
4×3 (odd number not good)
8×6 (6 is not evenly divisible by 8 or 4)
16×12 (12 is divisible by 4 but not 8 or 16)
32×24 (it’s 4×3 ratio and both numbers are divisible by 8, that’s good). So this is a pretty good base unit of measure.
64×48 (this is ideal since both numbers are divisible by 16 evenly).

Keeping these ratios in mind, divisible by 16 best, 8 good, 4 ok, you’ll find that:
512×384 is divisible by 16.
544×408 is divisible by 8.
528×396 is divisible by 8.

540×400 is close to 544×408 so the distortion might be too small for your eye to notice. You could go with that and crop a few pixels so it doesn’t distort instead.

BTW, you might see some sites use
240×180 (divisible by 8) for their smallest frame size and others use 256×192 (divisible by 16). 320×240 is divisible by 16.

For those who want to look at this another way. With 720×480 non square which is 640×480 square, you can get target frame size by:
64 by 48 multiplied by n (best frame sizes)
32 by 24 multiplied by n (best and good frame sizes)
16 by 12 multiplied by n (best, good and “passable” frame sizes)

I hope I haven’t muddied the waters too much but I thought the above might explain some ways to figure out frame sizes that don’t distort and work well for encoders.

[Rich Rubasch]

More detail….see if I can get my typos under check…

The true 4 x 3 equivalent to 720 x 480 is in fact 720 x 540. However DV video has 6 less lines than D1 NTSC (720 x 486) so you just can’t stretch it up to 540 vertical lines…that’s where 534 comes in. But 720 x 534 is not in fact true 4 x 3, so it is not a true downscale to 640 x 480. I use cropping in Cleaner or other encoder to remove lines to create the 4 x 3, then do the scaling.

I also use the multiple of 16 if I can…usually I can get there, otherwise I use the multiple by 4 method.

The key is that if you know the encode is going to look a lot better if you stick to these basic rules, you have apretty good argument for your client why you are suggestng to tweak the frame size a bit. Usually a player frame can be adjusted in a small way to make it work.

Good luck,

Rich Rubasch
Tilt Media

[Craig Seeman]

[Rich Rubasch] “The true 4 x 3 equivalent to 720 x 480 is in fact 720 x 540.”

There’s much discussion as to what “true” is when it comes to aspect ratio. I’ll point to this well researched article for those who don’t mind video engineering math.

https://lipas.uwasa.fi/~f76998/video/conversion/
One might look at this chart and the “notes” section too.
https://lipas.uwasa.fi/~f76998/video/conversion/#conversion_table
also this
https://www.lurkertech.com/lg/pixelaspect.html

[Daniel Low]

ON2, the makers of the VP6 CODEC used in Flash recommend frame sizes divisible by 8.

[Eric Murty]

Thanks to all for you’re replies. This has become very technical not really the intent. I presumed it was a little easier than this but I guess not.

Danny2007 you mentioned ON2 says the frame sizes has to be dividable by 8 does this mean I could use something like
544 x 360 or am I getting the math completely wrong.
544/8=68
360/8=45

Thanks,

[Craig Seeman]

Please do reread my first post

32×24 (it’s 4×3 ratio and both numbers are divisible by 8, that’s good). So this is a pretty good base unit of measure.

32 by 24 multiplied by n (best and good frame sizes).

Both the height and width would be evenly divisble by 8. The relationship between the two is 4 to 3.

[Rich Rubasch]

…AND 3 divided by 4 = .75.

So if 544 will be your horizontal resolution, then you would use 408 for your vertical resolution. Both are divisible by 8 and 544 by 408 is an exact .75 ratio or 4 x 3.

Rich Rubasch
Tilt Media