Correct aspect ratio for a PAL letterboxed movie?

Jnzk · Post by **Jnzk** » Thu Oct 16, 2003 2:51 pm

I'm planning to make an AMV from a PAL DVD. The movie it contains is letterboxed widescreen. I'm planning on using Huffyuv clips when editing so I'd like to get the source to look "correct" right in the beginning.

When I crop all black away the resolution drops from 720x576 to 694x420. Now what confuses me is the TV/PC pixel aspect ratio thing. If I'm correct PAR is 0.9 in NTSC televisions, 1.076 in PAL and 1 in PC monitors. That's what I could decipher from Premiere. The video is mostly intended for online distribution, but I might send it to American cons too.

How should I deal with the PAR? If I want it look right on a PC my simple math tells me that I should resize it to e.g. 640x363 (rounded to a multiple of 16 of course). Is this correct? What about con submissions then?

SS5_Majin_Bebi · Post by **SS5_Majin_Bebi** » Thu Oct 16, 2003 11:11 pm

That sounds pretty OK to me. I use PAL source as well (part of being an Aussie I guess) and whenever I resize anamorphic source or cropped letteboxed source, I use something like 320x180, or 640x360, and it comes out looking fine.

the Black Monarch · Post by **the Black Monarch** » Sat Oct 18, 2003 3:47 am

I have stuff that was originally PAL but formatted for NTSC. To get the pulldown pattern right, I have to select 83 out of every 199 frames (after Doubleweave, of course). Joy.

When it comes to your problem, though, your footage seems to be a 1.6524:1 aspect ratio, which I've never heard of. If you squoosh the pixels to 1.076, then the ratio becomes pretty close to 16:9, which is a bit more reasonable and probably what the movie was originally filmed at. If you must keep the exact original aspect ratio at all costs, and the dimensions must be multiples of 16, then your aspect ratio options are as follows:

256x144
512x288
768x432
1024x576
and anything bigger is totally ridiculous

You'll probably have best luck with the second and third ones. I hope this helps.

Jnzk · Post by **Jnzk** » Mon Oct 20, 2003 3:58 pm

I found Gordian Knot to be very helpful in making these calculations with cropping and everything taken into account. I guess I'll go with 640x352...

the Black Monarch · Post by **the Black Monarch** » Wed Oct 22, 2003 2:26 am

But that results in a 1.82:1 aspect ratio, when what you need is 1.78:1

Seriously, use 512x288 or 768x432! They're PERFECT.

Corran · Post by **Corran** » Wed Oct 22, 2003 6:27 pm

Whoa, whoa, whoa, hold on I thought we were talking about american con submission ratios...

For online distro 640x360 is an absolutly fine resolution. It's the horizontal resolution that typically has to be in multiples of 16. Don't use 640x352 unless you want the video the video to have distortion of eight pixels.

Now, as for con submissions you need something with a pixel aspect ratio of .9

Region 1 dvd's, which are ntsc of course, use a resolution of 720x480 which when converted to a square pixel aspect ratio is 640x480. This can be found by multiplying the horizontal resolution by .9

Anyways If we're to convert 640x360 to an ntsc ratio you have a slight problem. You get 720x360. You need 720x480. But this is simple to fix.

In Avisynth (I hope you're learning to use this. If not go to E and AD's guide to all things video and audioand learn the basics right away!)

Anyways, in avisynth you can add black borders to the top and bottom of your video to correct this problem. In your avisynth script put the following commands. Note: replace the red text with the proper directory and filename of your file, but I'm sure if you used avisynth already you know that...

AviSource("Directory:\of\the\file\filename.avi")
LanczosResize(740,360)
AddBorders(0,60,0,60)

Next using the avisynth script in a program such as TMPEG convert the footage into MPEG2. (Assuming your trial period is still good or you purchased the right to use its MPEG2 compression capabilties.)

There, you now have a 720x480 MPEG2 file that you can submit to cons.

Jnzk · Post by **Jnzk** » Thu Oct 23, 2003 3:01 pm

Yeah, I know how to add borders etc. in AviSynth. I'm just a sort of perfectionist who wants to get everything exactly right. I got very confused when I really began to think about all the different pixel aspect ratios there are... Sigh. I still am.

Corran Productions wrote: For online distro 640x360 is an absolutly fine resolution. It's the horizontal resolution that typically has to be in multiples of 16. Don't use 640x352 unless you want the video the video to have distortion of eight pixels.

I thought that e.g. DivX worked in blocks of 16x16 pixels. Couldn't a vertical resolution of 360 cause some problems?

Corran · Post by **Corran** » Thu Oct 23, 2003 3:17 pm

I'm working on a project now that uses 640x360 res video. I just saved part of a clip with Divx 4 compression and it works fine for me.

I don't have Divx 5 readily availible to test it as well but I imagine that it should work.

As for the divisible by 16 stuff take the common monitor resolution of 800x600 for example. 600 is not evenly divisible by 16. For verticle stuff I imagine that it has to be in multiples of eight but don't quote me on that.

err... though I guess monitor resolution itself doesn't really pertain much to the divx codec.

AbsoluteDestiny · Post by **AbsoluteDestiny** » Thu Oct 23, 2003 6:35 pm

non mod 16 resolutions DO cause problems with divx and mpeg.

Sometimes they may not be noticable but it increases the chance of edge distortions (often leaking of green chroma and other nasties) and various other issues.

I've done videos that are fine but then I've done some that have visible problems. However, it will make things much easier on the encoder (and decoder) if you just keep everything a multiple of 16.

Corran · Post by **Corran** » Thu Oct 23, 2003 6:54 pm

Ahh clarity. Thanks AD.