Determining Aspect Ratios and Resolutions

[Wilbert]

Let's see ...

It may be useful if you tell how many black borders your dvd has.

Assuming non-ITU (and anamorphic): 480*16/9 = 853.

Which means you should resize to 853x480 (or 640x360) for 1:1 playback.

The real aspect ratio is 2.35, which means 853.333/2.35 = 363, and thus 480-363 = 117 black borders on top and bottom (before any resizing). You should check this.

Thus resize to 480x360 and add borders to get 480x480.

[absinthecarolinas]

WAIT A MINUTE !!!

There are black borders in the MPEG itself of 2.35:1 DVDs.

(Let me repeat that so I can be sure to get it through my thick skull)

"There are black borders in the MPEG itself of 2.35:1 DVDs."

You see, DJRumpy ... I told you it was probably a mistake on my part. :P

I can't believe I've just spent hours encoding empty black bars for nuttin'!

Ah well, at least it all makes sense now

Thanks guys,

-abs

[DJRumpy]

If you aren't cropping off any existing letterboxing before your lanzosresize command, or with your lanczosresize command, you'll get a picture that is one aspect off like you describe (i.e. 1.33 look like 1.78, or 1.78 looks like 2.35).

Good catch Willard.

[Wilbert]

If you aren't cropping off any existing letterboxing before your lanzosresize command

? He shouldn't crop anything.

His svcd is squeezed because he squeezed his video too much during processing (480x272 instead of 480x360).

[absinthecarolinas]

With 480 x 480 SVCD as an example, it seems like the result would be the same whether you don't crop and resize to 344 vs. you do crop and resize to 272.

But wouldn't it be preferable to crop first? I dunno ... seems like either way you're encoding black bars.

-abs

[Wilbert]

With 480 x 480 SVCD as an example, it seems like the result would be the same whether you don't crop and resize to 344 vs. you do crop and resize to 272.

True, so DJRumpy was also right. Sorry about that.

But wouldn't it be preferable to crop first? I dunno ... seems like either way you're encoding black bars.

Some people do that because that prefer to run filters on the image without the black borders (you might see "artefacts" if you don't crop them away). So

Crop(...)
LanczosResize(...)
Filters ...
AddBorders(...)

But if you don't run any additional filters, it doesn't matter.

[DJRumpy]

Wilbert, your thinking of a 16:9 DAR for a 2.35 aspect video. SVCD uses a 4:3 display aspect ratio (DAR), so the height must be adjusted to compensate. The true width of a 4:3 MPEG is 640 (480 * 1.333 = 640), not 852.

640 / 2.35 = 272

absinthecarolinas, I always crop with my video using the extended syntax for the LanzosResize command. I prefer to know that my letterboxing is exactly where I want it.

For example, using the extended syntax:

LanczosResize(480,272,0,60,720,360)

The above will basically grab only the dvd image area of a 2.35 DVD video, and resize it into a 4:3 DAR, using a new resolution of 480x272.

[absinthecarolinas]

absinthecarolinas, I always crop with my video using the extended syntax for the LanzosResize command. I prefer to know that my letterboxing is exactly where I want it.

Very cool. Thanks for the tip. Say goodbye to the Crop command

I'm loving this new AVSEdit tool. A bit buggy but looooooooonng overdue. It's worth getting just for the help file included.

-abs

[DJRumpy]

I just downloaded the web sites manual via Internet Explorer. Makes a handly little local reference manual for those little used commands.

You'll find a sligt increase in speed by using the long syntax of the resize command. That syntax works for all three resizers (Bilinear, Bicubic, and LanczosResize).

[ericy5150]

DJ,

I have a 640X352 25fps xvid which I am going to convert to NTSC widescreen DVD for myself using your great guide! My question is, I have a friend who only has a regular 4:3 television and even though you get to see the whole image with widescreen, they have a small television and the black bars at the top and bottom make it even smaller. I know how to use virtualdub to determine letterbox top and bottom cropping for avisynth, but how do I determine the side cropping? I tried to just crop top and bottom and resize to 720X480, but on the beginning credits, half of the words are cut off on the side of the screen...anything I can do to resize this and keep the credits and such from cuttingoff..should I use 480X480? Thanks!!!!

[DJRumpy]

You can do a dirty side crop to convert a widescreen to a fullscreen, but when you do so, you take the risk of chopping off something from the sides, just as you found. The end resolution doesn't matter as long as it's a valid DVD resolution (480x480 isn't a valid dvd resolution by the way).

The only way to convert a widescreen to fullscreen without doing a true pan & scan is to simply crop the left and right sides off. To do this, you resize it to it's fully expanded width. Determine the aspect ratio (1.85 should be close enough for your avi). Then resize it to 852x480. You would then crop enough off of the sides to have the output = 640x480 (852-640 = 212). You then divide 212 / 2 = 106. You would crop 106 pixels from the left and right side to output 640x480 avi.

The last step is to resize your avi to a standard pal 4:3 DVD resolution, and then encode to mpeg.

A Pan & Scan converison would scroll around the widescreen to ensure all of the important elements remained onscreen after the size is reduced (imagine recording a widescreen movie with a cam that captures only in 4:3..you would move your camera around to capture any action that was happening on the widescreen). You would typically need video equipment to accomplish a pan & scan conversion.

[ericy5150]

Thank you so much! You always take time to give clear answers to our questions! What would I do if I wanted to get it to an NTSC resolution..in the last step before CCE encoding just use lanczos to resize to 720,480 in the avisynth script.. correct? I assume I'm using virtualdub to resize my avi using direct stream copy? THANKS!!!!

[DJRumpy]

You can use virtualdub, but when you crop it, you cannot use direct stream copy. Use Full processing mode. I was actually assuming you were using AVISynth, but either method will work fine. For NTSC, just resize it to 720x480 after you crop the left and right sides of the video. Also make sure you don't forget to slow down the frame rate from 25 fps to 23.976 fps.

[EddyH]

Actually I would still prefer to crop - if you crop it to get a nice hard edge (i.e. the picture goes right to the edge of the frame - you might lose a half pixel or so of the original) then resize it to a multiple of 16, then your black border will start sharply on the boundary between two blocks. It will also be purest black all the way through - both of these things adding up to both a (possibly considerable..) bitrate saving, and losing a lot of "dirty black" and soft / mid-block edge artifacts.

(yes, i've seen a few DVDs where the borders weren't actually pure black, had soft or mid-block edges, and seemed to be the original ones from the film... (?!))

Just a thought, yall.

[DJRumpy]

Your making it harder than need be. DVD has plenty of bitrate to spare. In regards to cropping, it's not needed. Just black out the edges if your concerned about dirty edges, rather than cropping (just lay the color black over the existing image area). Much easier and faster

[carbon21]

Hi i am trying to create a dvd for a film club showing movie trailers which are in mov format some are 16:9 and some 4:3 and some don't seem to be either! checked & scaled up using avi resize. i want to show the first trailer then cut to a still using mem on tv pan & scan then onto the next trailer. how can i use all the trailers whilst keeping the aspect ratios? i have memories on tv to create the show, tmpeg xpress to encode. I also have dvdlabpro.

i hope you can help as this is driving me crazy

carbon21

[EddyH]

may as well make it as good as you can, dude. it's not a great deal of extra time to do the maths and set the filter up (and basically zero, or even negative - once encoding is considered - extra CPU time) to claw back a few - or perhaps a surprising many - bytes per frame that might be useful elsewhere.

plus it means extra bits available in every frame for the actual picture information and less chance of the motion estimator acting up and sucking bandwidth

oh and i realised the easy way to figure out your vertical height... someone may already have said, but im tired and its late late late

NTSC material..... 4:3......
vertical height is nearest multiple of 8, after dividing 640 by the aspect ratio (1.33 for full screen, 1.56 for 14:9, 1.78 for 16:9, or 1.85, 2.11, 2.35 widescreens)

16:9.... multiply that height by 1.33.... if over 480, divide it by 480 and instead reduce the width (whatever it is for your chosen output - 320, 352, 384, 432, 480, 512, 528, 544, 576 640, 704, 720, etc) by that number, leaving the height at 480 itself

PAL.... same idea, but use 768 as your starting number, and when it comes to widescreen, you're looking at 576 not 480.

obviously these are halved for VCD, and you can tweak them up/down for divx by suitable amounts. best to take ntsc 640x480 as your basis even if the source is pal, as divx is rarely wider/taller than this.

[DJRumpy]

I really need to find out why I'm not getting notices on these...

carbon21: What your asking for is really simple when taken in small parts. The first thing you must do is determine what each video clip's aspect ratio is. Essentially you'll treat each clip seperately, processing it until it is the same resolution as all the others. Adding or removing letterboxing as necessary to retain the aspect ratio while resizing the clips to a standard dvd resolution. Since your source files are MOV, your clips should already be in the correct aspect ratio. Just divide the width by the height to get the aspect ratio. Your clips should not have any letterboxing. If they do have letterboxing, you must subtract the letterboxing pixels from your math to get an accurate aspect ratio. From there you would resize each video to a standard resolution (without letterboxing) and then add letterboxing to make the final output resolution dvd standard. A few samples of resolutions without letterboxing:

720x360 = 2.35:1 (anamorphic widescreen)
720x460 = 1.85:1 (anamorphic widescreen)
720x480 = 1.77:1 (widescreen)

640x480 = 1.33 (Fullscreen within a widescreen 1.77 aspect ratio. You would add letterboxing on the left and right sides rather than top and bottom)

Of course the 1.33 doesn't have any letterboxing, and neither does the 1.77 widescreen. Both fill the screen completely.

So if, for example, one of your clips turned out to be 1.85:1 video, you would resize it to 720x460, and then add 10 pixels of letterboxing on top, and ten pixels of letterboxing on bottom, which would fill out your resolution to 720x480.

[carbon21]

DJRumpy:
thanks for the reply Is there a program i should use to determine the size or does tmpenc3xp report the size accurately? i have gspot but it doesn't work on mov files, also how do you measure a file without including any letterboxing? Adding letterboxing afterwards i assume this can also be done in tmpeg3? havn't really had to use that part b4. you also mention resizing to a standard resolution is there an easy way to find out what these are or do you resize to 720 x something keeping the aspect ratio the same and then add the bars? Sorry to be a pain but quite new to this part of encoding & dvd compliant structure. thanks a lot hope you can help with these futher points
Carbon21

[DJRumpy]

Hmm.. I don't mess with MOV files. I'm guessing TMPGenc reports the proper size if it's reporting anything. If you use TMPGenc, try using the Center - Keep Aspect Ratio setting. It should automatically letterbox where needed without you doing anything at all. I already posted the resolutions you can resize to depending on what aspect your source is. You can use the crop tool to remove any letterboxing (if any) to see what the remaining image are is. For example, if your MOV is 640x480, and you remove 104 pixels of letterboxing from teh top and 104 from the bottom, you would have a video that is 480 - 104 - 104 = 272 or 640x272. You would then divide the width by the height to figure out the aspect ( 640 / 272 = 2.35 ). You could then resize to 720x360 per the 3 options below.

720x360 = 2.35:1 (anamorphic widescreen)
720x460 = 1.85:1 (anamorphic widescreen)
720x480 = 1.77:1 (widescreen)

[carbon21]

DJRumpy:

Ok i think i've got it now I will check it all out. Thanks for the quick reply much appreciated

Carbon21

[hashaam83]

DJRumpy,

first of all u did a gr8 job in creating such an excellent guide. i alwayz had a problem understand ARs. now, after reading yer guide, i can say proudly tht i have some knowledge of ARs.

ive gone through yer entire guide and could not (or, i must have missed it) find any information on video sources that do not have standard ARs.

let me continue with an example.

i have a AVI Source @ NTSC (23.976 FPS) which has following settings:
FPS: 23.976
Resolution: 576 x 304 (w x h)
Aspect Ration (Video): 1.895 (576 / 304 or 36 / 19)
Original DVD's AR: 1.85 (Widescreen, googled websties for this movie)
Letterboxed: NO

now, im converting this to NTSC DVD. ive checked in yer guide (another guide for converting AVI to DVD) tht i should stick to 1.85 AR and Resize my Video to LanczosResize(720, 460) and add borders AddBorders(0,10,0,10) in AVS script. but, after doing this, when i play the AVS file in Media Player Classic, i see the Video is stretched Vertically.
this is problem no 1. how can i solve this problem ?

after reading yer guide and understanding ARs i decided to do a simple math myself:

576 x 304 (Source AVI Resolution)
720 x YYY (Final NTSC DVD Resolution required, YYY being the height to find).

so will be having this way:

(576 / 304) = (720 / x)

after cross-multiplying:

x = (720 * 304) / 576
x = 380 (rounding to nearest 4) = YYY (required height)

now, NTSC DVD has a resolution of 720 x 480 so now i need to find out letterboxing for my newly calculated height. this will be

480 - 380 = 100
100 / 2 = 50 on top and 50 on below

so finally i need to use :
LanczosResize(720,380)
AddBorders(0,50,0,50)

if i choose the 2nd option, i have no video stretching. but i wud like to know is this method correct and will comply to DVD Player setting.
also it will be of gr8 help if u let me know a solution for Problem 1.

thanx in advance.
hope, ive made myself clear in asking 2 questions.

hashaam83

[manono]

Hi-

after reading yer guide, i can say proudly tht i have some knowledge of ARs.

Maybe less than you had thought.

i wud like to know is this method correct

No, just do it as he said. Your .avs is being resized 1:1 and looks OK now, but when encoded as 16:9 and resized by the player, will then look "squashed", or stretched horizontally. His script, on the other hand, looks stretched vertically now, but after encoding as 16:9 and being resized by the player will then look "normal". Maybe this will help to explain it better:

http://www.doom9.org/aspectratios.htm

[hashaam83]

now im totally lost. i thought i had reached somewhere.

can sum1 plz help me out here.

hashaam83

[DJRumpy]

Media Player Classic doesn't understand display aspect ratio. Because your video is anamorphic, it's actually wider than 720x480. When you encode it to dvd, you encode a 1.85 aspect ratio and squeeze it into a 1.77 aspect ratio by scaling the true full width back to 720 pixels wide (you've basically resized your 852x480 video into a 720x480 video. This is what makes it look tall. When the mpeg is played back in a player that understands DARS (Display Aspect Ratios), like WinDVD or PowerDVD, it is stretched back out to it's full width/aspect. If a player doesn't understand DARS though, it will look "tall" on playback.

Your mpeg is probably fine. Just burn it to dvd, and it should play fine on playback.

Your original sizes were the correct ones. Resize your output to 720x460 and add 10 pixels of letterboxing to the top and 10 to the bottom to increase the vertical size to 480. You shouldn't play MPEG with Windows Media Player. It's not designed for it, and tends to be glitch at best, and misreport all sorts of info at worst. Get a proper player like WinDVD, PowerDVD, Zoom Player, etc.

[CartManiak]

How would you handle an aspect ratio greater than 2.35? I've come across a few xvids with a 2.5 AR.

640 x 256 for example

I tried using the 2.35 avisynth script when converting to dvd with CCE. Everything looks fine aspect ratio wise, but black bars are actually encoded to fill out the space. Is there a way to just encode the actual video area of 640 x 256?

[manono]

No, because your video is wider than 1.78:1. If you want to keep aspect ratio, the only way to do it is by adding the black bars. Encoding to 16:9 will add smaller black bars than will encoding to 4:3, but there will still be a lot of them.

If you want to fill the screen with active video and still keep the AR, the only alternative is to crop the heck out of the sides of your 2.5:1 AVI. Personally, I wouldn't recommend doing that.

[DJRumpy]

Agreed. I would rather see letterboxing than chop a video up. Even when I had a 4:3 TV, I much preferred the letterboxed editions. To find out what ot resize it to, just divide the true width by the aspect, or multiply 480 by the aspect.

Since the true width is much wider than what normally goes into anamorphic dvd, i'd probably try dividing 852 / 2.50 to get the image width.

852 / 2.50 = 340

Round that to the nearest 8, which is 348.

Resize your video to 720 x 348 and add letterboxing to fill the 348 out ot the full 480 height. Encode it as 16:9.

[bluedevlx]

one post is enough, https://www.videohelp.com/forum/viewtopic.php?t=276110&highlight=

/Baldrick

[Matryx]

I'm trying to convert my avi to dvd format using mainconcept encoder. I don't fully understand this since I'm pretty new to the encoding scene so bear with me.

Here is info I get with AVIcodec for the avi I want to convert to DVD format.

1360 Kbps, 25.0 fps, 640*272 (2.21:1), XVID = XVID Mpeg-4, Supported
448 Kbps, 48000 Hz, 5 channels, 0x2000 = AC-3 ACM Decompressor, Supported

So the resolution is 640/272=2.35 Aspect Ratio. I would have to convert this to 4:3 Aspect Ratio.
the avi is in Pal format so I use 576*1.78 the aspect ratio that I want and it result to 1025 then I divide it with the avi's AR. 1025/2.35= 436

so 436 should be the height I used to put in Mainconcept Encoder in the Crop and Scale section right or am I getting it all wrong?