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View Full Version : Apect Ratio/Resolution question


yetanotherid
16th December 2008, 05:13
I've recently been doing a bit of comparison converting using the two different resizing options in AutoGK (default and UTI). As a result, I noticed that AutoGK doesn't always produce a video of the advertised resolution. However, when comparing the converted video to the original, especially when using the default resize method, this seems to be a good thing.

For example at one stage when using one of the resizing methods (default I think) I was running two pass encoding while slightly increasing the file size each time. AutoGK told me it'd produce a 720x304 each time. The first time the quality was a little low. When I increased the file size for the second conversion quality was better. When I increased it a third time AutoGK told me the quality would be lower again because I was now getting a 720x320 AVI. So I increased it a forth time to achieve a 720x320 AVI of better quality. Only thing is, every AVI AutoGK produced was still in fact only 720x304.

Then during some more testing on a different video I seemed to get results somewhat "opposite" to the first ones.
I converted a different video once using each resizing method. The resulting AVIs were, according to AutoGK, 720x304. The conversion using the UTI resize method was, but the conversion using the default method was 720x320. When playing the original video and comparing it to the converted videos, the incorrectly labelled AVI, the one using the default resize method, seemed to be pretty much identical to the original. So to my way of thinking the fact that I got an AVI of the "wrong" resolution using the default resizing method was a good thing. The UTI resized AVI looked a little vertically "squished".

For the record.... I used the Nero media player, Windows Media Player and Media Player Classic to look at each video to confirm each was being displayed the same way by all three players. They were, so either all three players display the video correctly, or they all get it the same sort of wrong. I then used Media Player Classic (and ffdshow) to compare the AVIs with each other and the original.

Why does AutoGK advertise one resolution, but sometimes produce an AVI with a slightly different one? And why so far has that appeared to be a good thing, at least when it comes to producing an AVI that's the same aspect ratio as the original?

That brings me to the next.... I'm going to open the can of worms.... question. I've read a few threads now explaining why the UTI resize method is better than whatever the default method is, only I'm not seeing it. Every conversion I've done using both methods has given the same results. The AVI produced by the default resize method looks closer to the original. Even when the resolution is the same regardless of which resizing method was used, the UTI method always seems to introduce some type of "distortion". So why do people recommend using it?

Thanks.

Brother John
17th December 2008, 19:44
It’s ITU (International Telecommunication Union), not UTI. And actually the ITU method is the default one, i.e. the one defined in an international standard. The other one (which you call default) is usually referred to as »generic«.

To make a long story short: Not one of those methods is always right or wrong. It all depends on the method originally used for producing your source video. However mostly there’s no reliable way to find out, so stick with whatever method you’re subjectively happier with and don’t worry to much about it.

manono
18th December 2008, 03:31
Hello, Brother John-

Your response (use whatever makes you happy) was pretty much what I told him in a different thread. However, non-ITU resizing is default in AutoGK (which is what he meant), and you have to go into the Hidden Options to switch it to use ITU resizing (which is what I had recommended).

yetanotherid
18th December 2008, 06:16
LOL. Not idea why I was typing UTI. But I'm a bit dyslexic like that. You should see me with phone numbers. Sometimes I actually watch myself write them down wrong as I repeat them back correctly....

But anyway the resizing thing wasn't really the purpose of the thread and I guess it's a question that will never have a right or wrong answer, but I am curious as to why AutoGK was telling me it had chosen one size while it in fact produced another. Under some circumstances anyway....
I've never checked up on AutoGK as far as resolution goes before. I always assumed it was giving me what it told me it would. I'll have to keep a bit more of an eye on it from now on to see if it's something which happens regularly.

Brother John
18th December 2008, 16:27
No idea why AutoGK would choose different heights for different file sizes. Maybe if you still have the log files there could be something interesting in them …

@manono
Ah, good to know. I actually never used AutoGK because I ditched AVI before AutoGK even existed. :)

len0x
18th December 2008, 22:52
Please produce the log files from two encodes that resulted in different hight, but with the same width. I'm curious to see them as I don't expect this to be happening normally (unless different ITU option was used).