Combining 4:3 ratio with 16:9 ratio footage

rubyeye · Post by **rubyeye** » Sun Feb 15, 2004 3:13 pm

I havn't done this before so I'm wondering if there is anything "special" I have to take into account when combining to use footage from a TV/OVA series with one that is letterboxed or "widescreen".

What dimensions would I be working with in Premiere?
And wouldn't one source or the other be distorted to some degree?

Basically, how would I work with them?

BigDude · Post by **BigDude** » Sun Feb 15, 2004 3:50 pm

I had always thought you would leave the OVA as letterbox or widescreen, then take the TV and crop it so that it is letterbox or widescreen as well. (?)
Then edit as you would anyway.

I dont think there would be any distortion that way. I havent tried it myself, so Im not too sure.

godix · Post by **godix** » Sun Feb 15, 2004 5:19 pm

You have two choices if you don't want to distrot anything. Either clip off the top and bottom of the 4:3 source to match the wide screen or trim the edges of the wide screen to make it 4:3. Trimming the edges of the wide screen would probably cause less problems in the long run.

If you don't want to lose any of the picture then your other alternatives are to either stretch out the 4:3 or shrink the 16:9. Both with introduce distortions though, you'll just have to look at the footage and decide which looks better distorted

el jacko · Post by **el jacko** » Wed Feb 18, 2004 5:31 pm

Can't you just add black bars to the top and bottom of the widescreen video, making it 4:3? That makes the most sense to me.

godix · Post by **godix** » Wed Feb 18, 2004 5:49 pm

Yes you could. Plenty of videos have been made that do exactly this. However they end up with half the video being in letterbox and the other half being in 4:3 which tends to not look good. If you convert one to the other though then most people don't even realized that the source had different aspect ratios.

Corran · Post by **Corran** » Wed Feb 18, 2004 6:38 pm

godix wrote:However they end up with half the video being in letterbox and the other half being in 4:3 which tends to not look good.

If you edit it without switching between the two aspects every other scene then it can actually help a video.

I wouldn't add bars though. If you want to have one still look like it is widescreen and the other full screen then I suggest resizing your sources to a square pixel aspect ratio and setting your project setting's res to 640x480. Then in Premiere 6.x (If that is what you're using) select the widescreen clip and go to clip -> Video options and select Maintain Aspect Ratio or else it will stretch your footage to 640x480. You will also have to go into the transparency settings for the clip and select the Alpha Channel transparency otherwise Premiere will add black borders to the widescreen footage. I suggest editing with Huffyuv or AVS files while doing this as I ran into some problems with the MJPEG swapping method when I tried this before. Might of just been the res of my source when I did it though (The verticle res wasn't divisible by 16).

the Black Monarch · Post by **the Black Monarch** » Sat Feb 28, 2004 9:10 pm

I was pondering this about 12-18 hours ago, and I came to the conclusion that both sources should be warped or cropped to an intermediate aspect ratio using one of 3 methods.

The first method is Vertical Lock. This is the method that I used for my Aliens/Alien3 music video. It works by expressing both source aspect ratios as fractions with a common denominator, and finding the average numerator. In this case, you'd expresss 4:3 as 12:9, then average it with 16:9 to get a 14:9 blend. You can either crop or warp; however, if you warp, then the 4:3 source will feature slightly more distortion than the widescreen source, and if you crop, then you'll have to crop off more area from the 4:3 source than from the 16:9 source.

The second method is Horizontal Lock. It works by expressing both source aspect ratios as fractions with a common numerator, and finding the average denominator. In this case, you'd expresss 4:3 as 16:12, then average it with 16:9 to get a 16:10.5 blend. It features the opposite problem of the Vertical Lock method; namely, the wider source footage will have to be cropped or distorted slightly more than the 4:3 source.

There is a way to find an intermediate ratio that distorts or crops both sources equally, and I call it Area Lock. However, it involves much hairier math and rarely results in a useable aspect ratio. It works by multiplying the two aspect ratios, and finding the square root of the product. In the situation that we're dealing with, the answer would be the square root of 64:27. This equates to a 1.5396:1 aspect ratio, which is best approximated by 20:13 (better approximations exist, but cannot be reasonably converted into whole macroblock ratios without taking up ungodly resolutions).

Warping is VERY easy and isn't too noticeable; if a 16:9 source was resized to 14:9, an originally perfect square would still be 7/8 as wide as it is tall. If you choose to crop instead of warp, you will have to do more math, resize, crop, and resize again, for one or both sources depending on the method used. For example, if I want to crop a 4:3 source and a 16:9 source so that both are 20:13: I'd resize the 4:3 source to 640x480, then crop 32 pixels off the top and bottom. The 16:9 source would be resized to 832x468, then cropped by 56 pixels from the right and left, then resized again to 640x416.

madbunny · Post by **madbunny** » Sat Feb 28, 2004 11:29 pm

Just so happens that this guide deals with this very issue, and gives you avisynth numbers to use.

the Black Monarch · Post by **the Black Monarch** » Sun Feb 29, 2004 12:07 am

The problem with that guide is that it likes to pretend all widescreen footage is supposed to be 2:1.

A 57:37 aspect ratio, best implemented as 912x592, is ever so slightly closer to the square root of 64:27 than the 20:13 ratio that I gave earlier. However, the resolution may be too big for some computer screens to handle. 640x412 is still (IMO) the best intermediate between 4:3 and 16:9.

the Black Monarch · Post by **the Black Monarch** » Sun Feb 29, 2004 3:08 am

I just realized that if you're not obsessively stupid about keeping things in their original aspect ratios, like I am, you could resize the 16:9 source to 740x416 (which is so close to 16:9 that it doesn't matter) and then crop 50 pixels off the top and bottom, eliminating the need to resize from 720x468 down to 640x416.

I need better ways to spend my spare time.