Resize and XviD settings

[SunMar]

Hello,

I'm trying to rip a DVD with Gordian Knot and although everything works, some things are still unclear to me.

The DVD is NTSC non-anamorphic 4:3 720x480 and after cropping the black borders it leaves 720x364.
To get an Aspect Error of 0% you'd have to resize this again to 656x364.

From what I gather by searching the forum, said in laymans terms and tell me if I'm wrong, it's resized to this by DVD players aswell and it's what you'd see on your TV aswell.
Even if size isn't a problem, it's better to have it resized like that rather then keep the original resolution.

Next are the W and H Modul settings. Usually it's recommended to just leave them at 32/16.
I already read that DivX encodes in macroblocks (no idea what those are though) of 16 so the more you go below that, the worse it is for the compressibility.
Next to that there's also a compatibility issue, some video cards want a resolution that's a multiply of 16 or 32 which means that if you go below that you can't play the movie, or at least not easily in full screen.
When it comes to this I have three question:
1) Does that no. 16 also apply to XviD or has it different numbers?
2) If you go below 16, would it really make a difference in compatibility, in other words are there a lot of video cards that really don't like it?
3) Compressability, compatibility, both nice but what about quality, how is the quality of the video stream effected by these two values?

The DVD I'm ripping right is compressing extremely well, so I either need to increase the resolution which means lowering the W/H-Modul settings (that above mentioned 656x364 is with an W&H-Modul of 4) or, and now for the second part of my post, understand more about the XviD codec so that I can boost the quality (and thus size) somehow with those settings.

Is there a site or thread or something where all the XviD settings are explained in detail?
All XviD guides I've read either do not go into the settings at all expect "check that, don't check that, etc" or only give an extremely brief description.
I downloaded a PDF document once which explained a lot of settings pretty nicely, but it was a bit out-dated so it didn't cover a few features and also didn't go into detail when it came to I/B/P-frames.
I'd like to really understand what everything does, how they affect quality, etc., because right now I don't have a clue about them and am all but pleased with how my avi's look for their size.
They're not bad, but looking at some of the things out there, they could definantly be better :).

Regards,

SunMar.

[manono]

Hello and welcome to the forum.

Some people may have other opinions about the questions you've raised, but here are mine:

To get an Aspect Error of 0% you'd have to resize this again to 656x364.

You can get whatever horizontal resolution you want. I wouldn't be dead set on getting 0% Aspect Error, though. I keep mine under .5%. You can't tell anything's off unless you get up around 2% Aspect Error. And you can always crop a few pixels into the video to improve on the Aspect Error. No big deal. You lose a lot more than that when playing the DVD, due to the TV's overscan. Oh, and I'd recommend resetting the H-Modul to 16. Your vertical resolution is only Mod 4.

it's resized to this by DVD players as well...

I didn't fully understand that one. The DVD gets resized by the player depending on whether the DAR is 4:3 or 16:9. An .avi doesn't get resized like that (unless you tell the player to do it), but just gets scaled to your desktop resolution when you full screen it (again, I'm not sure I understood the question). If you're asking if it's better to downsize and get 0% Aspect Error than to keep the higher resolution together with a small Aspect Error, then my first answer answered part of that. And I'll let the results of the compression test tell me how high of a resolution I can choose. But I don't mind downsizing to usually 640x272, or sometimes to as low as 576x256 or so for 2.35:1 movies. But this is your specialty, jggimi-any thoughts?

Usually it's recommended to just leave them at 32/16.

Advice you didn't follow. :)

1) Does that no. 16 also apply to XviD

Yes, and all MPEG4 codecs.

2) If you go below 16, would it really make a difference in compatibility

I believe the Matrox and some older cards don't like Mod 8 or lower resolutions (Hakko504?).

3) Compressability, compatibility, both nice but what about quality

Compressibility is directly correlated with quality. So, in the example that TheWEF gave in the Sticky (http://forum.doom9.org/showthread.php?s=&threadid=42708), using a Mod 2 Vertical Resolution resulted in about 5% less compressibility, and therefore about 5% less quality for the same file size (roughly speaking). As far as compatibility goes, if your vid card can't handle the resolution, you'll know it. It'll look real nasty, or maybe it won't play at all.

Is there a site or thread or something where all the XviD settings are explained in detail?

Have you seen the XviD FAQ (http://forum.doom9.org/showthread.php?s=&threadid=16935)? And there's plenty of information available in various threads in the XviD Forum.

I hope that answers most of it. And if anyone wants to correct me or add anything, then please do.

[SunMar]

I wouldn't be dead set on getting 0% Aspect Error, though.
Oh, I'm not too picky about stuff like that, it was just an example.

I didn't fully understand that one. The DVD gets resized by the player depending on whether the DAR is 4:3 or 16:9.
That's exactly what I meant ;).

Advice you didn't follow. :)
To be more preciese, advice I didn't read until after encoding :).

Have you seen the XviD FAQ (http://forum.doom9.org/showthread.php?s=&threadid=16935)? And there's plenty of information available in various threads in the XviD Forum.
Wuh ... I didn't notice that FAQ thread, weird :confused: :).
Going through all the various threads is too much work though, already tried several searches and most came up empty.
Don't want to stick a lot of time into that if there's a site around that explains it all :).

I hope that answers most of it.
Most of the stuff I asked about yeah, still got a lot more questions which is why I asked for a site/thread, but with that FAQ and the links that are in it those should get covered too.


Thnx for the reply :).

[jggimi]

...But this is your specialty, jggimi-any thoughts?...

Specialty? I just try to take a very complicated subject (Film DVDs -> AVI, and aspect ratios) and reduce it to simple concepts that are, uh, sufficiently simple that I can comprehend them. If I understand them, then I can usually explain them to others, like so: PC monitors, and video designed for PC display, use square pixels. Most monitors have 4:3 aspect ratios, and with square pixels, 4:3 is the same ratio as 1024:768, 640:480, and other common monitor resolutions.

Commercial DVD video streams do not have square pixels.

Commercial DVDs are all produced with a single standard pixel resolution. 720x480 NTSC (square pixels 1.5:1), or 720x76 PAL (square pixels 1.25:1). In addition, the video streams are tagged for display at either 4:3 (1.33:1) or 16:9 (1.85:1), the two aspect ratios of television sets. If you think in PC square pixels (like me), you can say that all DVDs are anamorphic.

Since films may be produced in a wide variety of aspect ratios, but DVD's only in two -- letterboxing is used whenever the film's aspect ratio is different than the DAR.

To display on a PC monitor with square pixels, software DVD players resize the video for proper display.

Encoding DVD's to AVIs requires the same sort of resizing. However, to reduce the size of the finished product, we crop to remove the letterboxing.

With the DAR set properly in Gordian Knot, cropping away the letterboxing, you should be able to pick resolutions which restore (or nearly restore) the film's aspect ratio. For example, Manono mentioned a couple of resolutions he has used with 2.35:1 films -- 640x272 (2.35:1) and 576x256 (2.25:1).

A "widescreen" movie on DVD may have either DAR. In addition, sometimes the DAR value in the MPEG-2 stream, used by DVD2AVI (and R4R), will be different than the DAR value in the DVD's .IFO file. DVD players use the data in the .IFO, so, for proper data, we're dependant on the production companies following the standards. This means that sometimes, you get incorrect DAR information.Now that we've level set, based on the limited information SunMar shared with us, I can share a couple of bits of math. This really shows my rather narrow grasp of the subject. Consume with care. Assuming that 720x364 (1.98:1) is after cropping, but prior to any resizing, and that the DAR is 4:3, the original film's aspect ratio is approximately 1.76:1.

Assuming that 656x364 is after resizing, the original film's aspect ratio is approximately 1.8:1

The difference between 1.76:1 and 1.8:1 may be slight, and may be due to checking (or clearing) the ITU-R BT.601 standard. Warning: There are many posts about the ITU standard that can be read in the forum. Let me clearly state for the record I understand none of them.

If the aspect ratio of the film (found on the box, at www.imdb.com, and other places) isn't close to 1.8:1, but is instead, closer to 2.4:1, review the content in Gknot's preview window, and try switching to 16:9, and see if round things look more round that way. 2.35:1 is a common film aspect ratio. I ask because if the DAR is 16:9, 720x364 (unresized) would be about 2.4:1 after resizing, and as I mentioned, sometimes we get the wrong DAR from the video stream.I hope this helped!

[SunMar]

Thnx jggimi, I think I finally understand the whole resize thing.

As for the limited information, sorry about that, but I'm trying to understand anything and if everything becomes too specific most of info in the replies wouldn't be applicable anymore when I try to rip something else :).

After reading some more still got some questions about all the XviD settings but I'll start a new thread in the XviD forum about them :).

[masken]

Thank you manono & jggimi, informative :)