Frame Size

[kamranj]

Hi All

I am newbie to this forum so appolagies if i am asking the wrong questions in the wrong places...

I recently bought a panasonic dmp-bd60 which plays divx xvid etc. I want to convert all my dvd's into xvid format so i can save about 5 shelves of space in the living room, to do this I am using AutoGK

The problem I have is my original frame size on my file suggests it is 720x576, reading other posts i belive this is standard format however when i convert the file into xvid format the file seems to squash down in height and i am not sure why..

i have read many posts on the site and to be honest there all a bit too technical for me, please can someone tell me if retaining 720x576 is possible, if so how? Should i be using any other type of software to achieve this?

Appreciate any help on this

Kam

[redwudz]

Unless it ends up at a much smaller framesize, and the aspect ratio is still correct, I wouldn't worry about it. The bitrate is more important as that determines the quality. Someone else can probably give you the technical reason for the odd frame sizes. I just ignore it if the video still looks good.

And welcome to our forums.

[kamranj]

thanks redwudz

picture still looks good, its just annoying that its smaller on my tv...

[intracube]

The problem I have is my original frame size on my file suggests it is 720x576, reading other posts i belive this is standard format however when i convert the file into xvid format the file seems to squash down in height and i am not sure why..

I think it's a compatibility issue with DivX and Xvid and anamorphic video. A common workaround is to convert the video so that it has 'square pixels'.

This site has an explanation halfway down the page:
http://www.divx-digest.com/articles/xvid_setup_page2.html
- 'By default, square pixels are used, but you can also define 16:9 PAL/NTSC pixels, which is the way anamorphic content on DVD is recorded (ie. the picture appears tall). Note that your encoding software (eg. Gordian Knot) needs to support this (and most don't), the file container (AVI, MKV) need to support this (most don't) and finally, your playback filter also need to support this (only 3ivX supports this at the time of writing). The default setting (Square pixels) is recommended.'

I don't know if AutoGK has an option to override this. Even if it does, you might find your films end up distorted or incorrectly formatted when viewed on your TV.

picture still looks good, its just annoying that its smaller on my tv...

Although the height is reduced on your converted films, your Panasonic player should format them correctly so they look the same as the original DVDs on your TV - except possibly with a softer image.

[PuzZLeR]

Are you experiencing this distortion on both PC and player, or just the player? I don't think it's a big problem, but if perfection is your objective then likely the culprit, at any rate, is Pixel Aspect Ratio (PAR).

PAL DvDs have a PAR of 16:15 (for 4:3 Display Aspect Ratio (DAR)) and 64:45 (for 16:9 Display Aspect Ratio (DAR)) otherwise they'd be distorted. This was so that the picture would fit for the TVs of the older area.

Formats like DivX/Xvid, and the AVI container, were designed for PC playback, and typically use square pixels (PAR = 1:1) and aren't reliant on DvD standards. Using square pixels on a DvD standard resolution of 720x576 would distort the picture for sure, which is likely your problem.

One of two things are happening to you I imagine:

Problem 1) You are encoding with square pixels but keeping the original source resolution. This will distort the picture.

You can encode to a PAR=1:1 friendly resolution of, say 640x480 for 4:3, or 640x352 for 16:9 (using 640x360 would be more mathematically valid in this case, but 360 is not divisible by 16 and could cause problems technically with the Xvid/DivX/AVI format).

Another suggestion is to use anamorphic encoding (using the correct respective PAR). However, being mostly a DivX user, I'm not sure if Xvid offers this option. If it does, then you can keep the resolution, and correct DAR, of 720x576 without distortion.

Problem 2) You are indeed successfully encoding with anamorphic (if it exists in Xvid) and your player suffers from the "Square Pixel Assumption Syndrome".

What this means is that many players will not honor anything other than PAR=1:1 in an AVI file. This is nothing wrong with AVI, or Xvid/DivX, just that these players are not very good decoders. AVI in general suffers from this disrespect, and if your Panny is one of these units that does so, you'd be better off encoding with square pixels to have a common denominator of compatibility among all devices.

FYI: A good equation is the following, and you will NEVER go wrong:

Width / Height = DAR / PAR

[PuzZLeR]

Ahh, intracube also suspects PAR issues - but I didn't mean to echo since we were posting at the same time.

[manono]

My own recommendation is to allow AutoGK to do the resize as it'll play with the correct aspect ratio in all devices, while you're taking a chance when playing them on standalones if kept at 720x576. However, to answer the question, yes, it's possible to avoid the resize and keep it at 720x576 by changing a couple of settings in the Hidden Options (CTRL-F9). A quick read of the included tutorial would have supplied the answer. You'll have to both disable the cropping and also have it keep the original AR:

Threshold defines how sensitive auto crop will be: the higher the value the more cropping will be done. To completely disable auto crop you can set threshold to 0.

Also, check the 'Override input AR' box and set it to 'Original'. And then, if you want it at 720x576, maybe go into the Advanced settings and set the width to 720:

http://www.autogk.me.uk/modules.php?name=TutorialEN#6

You do know, don't you, kamranj, that 720x576 is the wrong aspect ratio for playback? A DVD gets resized while an AVI doesn't ordinarily. As a result, people will look way too tall and thin if you keep the original aspect ratio. And AutoGK won't set a PAR flag for you to have it play back properly in the standalones that support the anamorphic flags. You'll have to do that afterwards using MPEG4Modifier.

[jagabo]

If you want to run a quick test to see if your player supports Divx/Xvid aspect ratio flags try the videos in this post:

https://forum.videohelp.com/threads/329066-Dar-sar?p=2038905&viewfull=1#post2038905

If they play with the proper aspect ratio, full screen on an 16:9 TV, or 16:9 letterboxed on 4:3 TV, your player supports the flags and you can keep the original frame size. In my experience most players made in the last several years support aspect ratio flags in Divx/Xvid AVI files.

[kamranj]

Hi All

sorry for the late replies

some updates..

If i allow GK to resize automatically the video does not play properly on my player, the height is chopped right down

jagabo - The two videos show up perfectly on my tv thanks for that

I then went and set the atuocrop feature in GK to 0 and set it to use the original aspect ratio, the video looks funny on my pc it seems to tall and narrow but plays perfectly on my TV

Just to experiment further i then set the minimum width to 720 and it generated a file of 720 x 544, this doesnt play on my tv, i think the reason is because the file generated is 2.4Gig and people suggest the max size the player can support is only 2G...

Tomorrow i will create another file and drop the quality of it to bring it under the 2G limit and see how that plays, i will post back my findings

Thank you all for your help so far, much appreciated

If anyone hinks i am going about this in the wrong way please let me know

kam

[jagabo]

Just encode with the exact same frame size as the source and use the PAR/DAR flags to set the aspect ratio. If those aren't playing with the correct aspect ratio on your computer you just need to figure out why (use the right player or fix the settings in the player you're using). Do the files I linked to play with the right aspect ratio on your computer? They should.

[manono]

If i allow GK to resize automatically the video does not play properly on my player, the height is chopped right down

If you're saying you're losing/missing video from the top and/or bottom, check it on the computer. If video is still lost, then something went wrong in the AutoGK crop. Post the log. If you're saying the entire video is there but that the height was decreased, then that's what's supposed to happen to get it to play with the correct aspect ratio.

I then went and set the atuocrop feature in GK to 0 and set it to use the original aspect ratio, the video looks funny on my pc it seems to tall and narrow but plays perfectly on my TV

I already told you you have to set the PAR flag afterwards using MPEG4Modifier to get it to play correctly. If your TV set plays it correctly, then you either have it set up incorrectly (4:3 instead of for 16:9 or widescreen), or you have one of those defective players that stretches everything to fill the screen. Check the player and TV settings. A 720x576 AVI without the flags playing on a widescreen TV should also play with people being too tall and thin, and should have black bars on the sides. Maybe your TV is in some sort of stretch mode, or maybe (as I said) you have your player set up to output for a 4:3 TV set.

i think the reason is because the file generated is 2.4Gig and people suggest the max size the player can support is only 2G...

If true, use AutoGK's 2-pass mode and set a size. And maybe lower the resolution to, perhaps, a 640 width. If you set the Target Quality for 100%, lower it to maybe 65%. No one can tell you how you screwed up without a log.

[PuzZLeR]

...or you have one of those defective players that stretches everything to fill the screen...

Although this is only opinion, I wouldn't say "defective" if so. I would just call it a "flawed design" that was approved after testing, or a "bad decoder", that comes in, sadly, too many players. Then again, it's all relative. I would simply blame it on manufacturer ignorance at any rate.

@Kamranj: Let me also suggest, as one option, you just encode to width 640 as Manono pointed out. This way you don't have to worry about any PAR flags, and you can count on all DivX/Xvid players playing it right without any distortion, even with the defective/bad decoder ones. (I will recommend a Lanczos resizer if available).

As well, it will reduce the file size even further and save some more of that precious shelf space you mentioned. Yes, 720x576 is indeed a PAL DvD standard resolution - but in the AVI/DivX/Xvid world it's a new game and this "standard" has nothing to do with anything here.

[manono]

Although this is only opinion, I wouldn't say "defective" if so. I would just call it a "flawed design" that was approved after testing, or a "bad decoder", that comes in, sadly, too many players.

A defective (or flawed) chipset makes for a defective (or flawed) player, doesn't it? I remember that all the players with the early ESS chipsets stretched 1.33:1 videos so they filled the widescreen TV sets and everyone looked fat. I don't really think that's the case here, though, but that kamranj has something set up incorrectly in either his player or his TV set.

[jagabo]

This is for the OP. PuzZLer knows this already.

Let me also suggest, as one option, you just encode to width 640 (square pixel)

If you do that you will lose about 10 percent of the horizontal resolution, and ~18 percent of the vertical resolution with 4:3 material or ~37 percent of the vertical resolution with 16:9 material.

it will reduce the file size even further

Only if you use a lower bitrate (specify a smaller file size) too. What he really means is the smaller frame size will allow you to use a lower bitrate without the picture degenerating into blocky artifacts. But what you are doing is trading away resolution to get fewer blocky artifacts.

[manono]

Only if you use a lower bitrate (specify a smaller file size) too.

I don't know for sure, and won't until I see a log, but I suspect he's doing one-pass Target Quality (quantizer) encodes with AutoGK. If so, then lowering the resolution can maintain the same 'quality'. And by definition both the bitrate and filesize will also be lowered. It makes sense (to me) that if he wants to get it under 2GB he might lower the resolution, the Target Quality, (raise the quantizer) or both. And if he's using a 100% Target Quality (quant 2), he can lower that considerably without getting any real noticeable artifacts.

[kamranj]

Hi all

so i had time to play around with today, first of all tv is set correctly 16:9 and player is also setup to output at 16:9

I found that if i set autoGK to set a target size output of 1.99GB, turn auto cop off and set the AR to original everything plays perfectly, there is no real notciable loss on quality either, i am now trying a file with 640 output jus for good measure to see what size file output that gives and also if there is any loss in quality, i will post my findings and logs here afterwards for everyone to see

Kam

[PuzZLeR]

i am now trying a file with 640 output jus for good measure to see what size file output that gives and also if there is any loss in quality

The file size will indeed be decreased reducing to 640 width, and I made that comment earlier on the assumption ceretibus paribus - that you encode with more-or-less similar settings, such as, for example, using constant quality.

Then again, since you do understand you will lose quality with whatever settings you do use with a lossy format like DivX/Xvid, and more still if you reduce resolution, it is worth investigating the 640 width option when using AVI, even if your player can handle flags other than PAR=1:1. It's still a good balance of quality/size and has good compatibility (without distortion) among all players, if migrating.

[jagabo]

i am now trying a file with 640 output jus for good measure to see what size file output that gives

The file size of a 640x480 encode and a 720x576 encode will be the same if you "set a target size output of 1.99GB". That's the whole point of picking a target file size. You're saying "I don't care what the quality is, good or bad, I want a file that's THIS size."

It's only when you use constant quality encoding that the file size will decrease with the frame size.

[manono]

first of all tv is set correctly 16:9 and player is also setup to output at 16:9

If the AVI is 720x576 out of AutoGK, if you didn't set a PAR using MPEG4Modifier, and if it stretches to fill the screen, then something's wrong. It should play with black bars on the sides. Didn't you say before that when played on the computer people are too tall and thin?

So, either you have your TV set set in some kind of a stretch mode, or your player is flawed (to use PuzZLeR's term ). Do you have any retail 4:3 DVDs with which to test, some old classic film, perhaps? How do they play? Same thing - stretched to fill the screen? Are you one of those people that doesn't like black bars on the sides and set the TV so you never see any?