Cropping by multiple of 16; help!!

[chipzoller]

Ok:

I got another question that I have been wondering about and just thought I would post it right in this thread.


first I apologize for my ignorance on this topic but I hope someone could help me out here.


first, I usually set my video resolutions to about 352X240 BEFORE cropping them. 352X240, as you all know, is VCD standard resolution. I make it that small because its pointless to making it bigger, or so I think but I could be wrong, because it would waste data encoding it larger. I just full screen it upon opening.


Now, I usually have DVDs that are in widescreen format (i.e. black bars at the top) so I will open them in Xmpeg 4.5 and AUTOCROP the black lines off the top so as not to waste space encoding black space. When I use the autocrop feature in Xmpeg it will crop off the black bars but if you are to look at the outline, which represents what will be contained in the crop, you will see that it doesn't perfectly crop the black bars out. Almost; very close to it; but not perfectly. Now, I know that people have said that you must make the dimensions AFTER the crop divisible by 4-8-16 or whatever everyone says. And AFTER the autocrop, I will make all the dimensions divisible by 4 and this allows me to start the encoding process.

My questions:

Why, when I'm using the same DivX codec, does Xmpeg from 4.2a to 4.5 either let you encode or not depending on whether you make the dimensions divisible by 4 (4.2a didn't care, maybe this was due to a perfect crop in those dimensions but later versions wouldn't let you start encoding until they were right).???????

and some people suggested to make it divisible by 16. This might help the playback or something along those lines. This is what I don't understand: You can't approximate your crop to be a multiple of 16 always because if you go too low or too high to reach that multiple of 16, you could either be chopping off some of your picture or leaving too much black bar in there. Maybe I'm wrong about this but I just don't understand how this is a valid solution. I guess what I mean is, how can I do this but still have 100% of my picture and no black bars?????



Ok, I think i've bothered you people enough about my problems.
Anyway, if anyone has any suggestions/solutions I would love to hear them.

thanks,




Chip

[Selur]

"first, I usually set my video resolutions to about 352X240 BEFORE cropping them. 352X240, as you all know, is VCD standard resolution."
If u don't encode VCDs use higher resolutions and you'll get more detailed results for the avi same size.

"I make it that small because its pointless to making it bigger"
Sorry, but all my experience tell me otherwise,...

"And AFTER the autocrop, I will make all the dimensions divisible by 4 and this allows me to start the encoding process."
go for div 16 or div32

"..let you start encoding until they were right).??????? "
If I'm not mistaken, earlier autocrop versions did automaticly watch so that output resolution was atleast div 4.

"I guess what I mean is, how can I do this but still have 100% of my picture and no black bars?????"
First u can't allways do it because some movies aren't div16 without black bars. But normally u can find a resolution which is div 16 when all the bars are off. Andeven if u can't find one, if u use a higher resolution e.g. 704*xy cropping of some pixel won't destroy so much of the movie. (if u stay with 320*xy you'll loose a lot more)

Cu Selur

[chipzoller]

Ok,

Well what resolution should I use before cropping??

I need something larger than what I have been using, according to your suggestion. so I'm using 352X256 I think, so what would you suggest to get better results???




chip

[chipzoller]

This is what I did before I posted that last message:


I made the resolution divisible by 16 BEFORE I started to crop. Now, when I hit AUTOCROP the individual values aren't divisible by 16 but it will still encode. So the only values that have to be divisible by 16 are the resolution values prior to cropping???



Also, do you suggest just leaving the resolution like the original??

740X480 or whatever it is




chip

[Selur]

My suggestion would be use 720*480 (640*xy) before cropping and crop manually so that you'll get a resolution that's div16 AFTER cropping.

Cu Selur

[chipzoller]

Ok,

Well can you tell me exactly what figures I should use?

720X480 sounds good. I am having Widescreen videos and wish to crop the black bars.

can i manually put in figures that are divisible by 16 then VIEW the effect the figures have on the resulting picture???

Every time I try to do that it always resets the figures to the values for the autocrop.




chip

[Nazgul]

Originally posted by chipzoller
Ok,

Well can you tell me exactly what figures I should use?

720X480 sounds good. I am having Widescreen videos and wish to crop the black bars.

can i manually put in figures that are divisible by 16 then VIEW the effect the figures have on the resulting picture???

Every time I try to do that it always resets the figures to the values for the autocrop.




chip

Any time I've ripped a hi-res source like that, I'll usually use 640x480 if it's non-anamorphic and 640x360 if it's anamorphic. Then I'll crop down to get rid of the letterbox bars. For a typical 1.85:1, try cropping down to 640x352 or 640x368, that should get you close. For CinemaScope movies that are 2:35:1, try 640x272 or 640x288.

If you want to keep the width at 720 like the original dvd, then you'd start with 720x540 or 720x405, and scale the cropping accordingly. It shouldn't matter what the original resized resolution is, it's the final output that should matter the most. However, depending on your program you might have to set them in a strange order to keep the program happy. Xmpeg, for example, can be real picky. If the un-cropped resolution I'm going to use isn't acceptable, then it won't let me switch to the cropping tab. So I set it bigger, then go set the cropping the way I want, then go back and set the un-cropped resolution. Kinda a pain, but it gets the job done and doesn't take -that- long if I know what settings I want to use. :)



Nazgul

[chipzoller]

OH man,

all this stuff is sooo confusing!!!





chip

[Nazgul]

Originally posted by chipzoller
OH man,

all this stuff is sooo confusing!!!



no kidding. that's why the best way to figure this stuff out is trial and error, because no matter what you want to do, you'll get 15 different answers on the best way to do it. :)


Nazgul

[Selur]

nazgul is right most of the people who 'know' what they are doing know it because they do this stuff a long time and tried a lot of settings ;)

So what u should keep in mind 320*xy sucks for avi's and most people prefer something from 572 - 720 after cropping.

Cu Selur

[Nazgul]

Originally posted by Selur
nazgul is right most of the people who 'know' what they are doing know it because they do this stuff a long time and tried a lot of settings ;)

So what u should keep in mind 320*xy sucks for avi's and most people prefer something from 572 - 720 after cropping.

Cu Selur

That's definitely true for hi-res sources, but when your source is a 352x240 VCD mpeg, I usually just go for 320x240, as I'm really not gonna get much more quality by upsizing it. Plus, filesize is a big priority for me, the small quality gain I -might- get isn't worth either the encoding time or the extra filesize. Plus, when I play my 320x240 Divx .avi's out to my tv, they look just fine to my eyes. But as with most things Divx, your mileage may vary. :)


Nazgul

[chipzoller]

Ok guys,

I'm really sorry to bother you again. But I am just not understanding this resolution shit.


I understand the process in xmpeg 4.5.


you put in a resolution before cropping. lets say for my sake 352 X 240.

Now everyone says after cropping it should be this. But I don't see where the resolution is after cropping. I know you can go to the output tab and drag the crop 'square' around just the picture. I don't really understand how the values influence everything and why for the requirements of multiple of 16 or 4.

can someone give me an idiot's guide or speak to me as if I know nothing about this subject?

I need to start from the beginning again with this.


thanks for ya'lls help.



chip

[Selur]

if u activate cropping u can use the cropping square to define what part should 'stay'.
In the upper left of the pic you shoudl then see something like 352x240 -> 320x160 which means you set the input resolution to 352x240 and defined a cropping square with the size of 320x160.

"why for the requirements of multiple of 16 or 4"
it's because some codec don't support resolutions that are not div 4 or div 16. Also hardware overlay support while playback wouldn't work with most of the graficcards out there is the resolution is not div 16.

Cu Selur

Ps.: hope this helps,..

[chipzoller]

Ok, I understand this. I'll try it out.

but once you select autocrop and the 'square' selects what stays then the values for 'offsets' change. I understand what the resolution will be once the square has selected what will say. It will list, in the upper left corner, the beginning resolution and then the resolution after the cropping.

so if the values aren't a multiple of 16 after cropping, what should I do to make them so? should I play around with the cropping square or edit values manually? that is why I am unsure of the values in the boxes. Usually you won't affect the horizontal length but the top offset and final length, or whatever it is, change.

Can you explain these?


thanks for all your help.



chip

[Selur]

"should I play around with the cropping square or edit values manually?"
Will have the same effect, but playing around with the square is more fun, so better do that. :D

"that is why I am unsure of the values in the boxes. Usually you won't affect the horizontal length but the top offset and final length, or whatever it is, change."
*gig* u have to see it from the fun side, u are not hurting anybody and the worst that could happen is that u somehow skrew up the file and you might have to do the encoding again, but then u at least learned how not to do it :)

Cu Selur