Aspect ratio slightly off? (Megui, Staxrip vs Xvid4PSP)

[ARTO65]

I have been searching for an answer, alas with no success.

I am trying to convert a DVD. The original resolution is 720x576.
When I convert it with Megui 2028 or Staxrip 1.1.7.1 (with x264), the output is slightly wider than the original.
I do not know how to find out the Display aspect ratio of the videos, but for example, when I put the videos in Handbrake with Strict anamorphic, I have:
Original video: 845x540
Converted video: 864x540

Meanwhile, other programs like Xvid4PSP 6.0.3 daily keep the aspect ratio intact.

What can I do to keep the exact same aspect ratio when converting with Megui ?
Thank you very much for your help!

[Baldrick]

Do you want to keep it in 720x576 with just a 4:3 or 16:9 display aspect ratio?

Most dvd converters crops the black borders and resizes it then to a 4:3,16:9 or 2:35:1 resolution.

[ARTO65]

Thanks for the answer, Baldrick!
Actually, I don't apply any kind of cropping or resizing.
In Megui, I simply index the file, save the script, then use the autoencode.
In Staxrip, I uncheck crop and deinterlace, then convert.

Do you know where the information about where the display aspect ratio can be found?
As I was saying, the only figures I have are 845x540 (original) vs 864x540 (converted file).

[manono]

Do you know where the information about where the display aspect ratio can be found?

GSpot, MediaInfo. However, you should be able to tell just by playing it. Does it play as 'widescreen' or as 'fullscreen'? The former is 16:9 and the latter 4:3.

[ARTO65]

Thanks for suggesting gspot!
I already had mediainfo, but I cannot find any meaningful info about the DAR. I only have an approximation which is 16:9 for all the videos.

Gspot reveals that the video converted with Staxrip and megui have a different DAR than the original video.
The original video is 1.778
The converted videos with staxrip and megui are 1.818
The converted video with Xvid4PSP is 1.778.

How can you make sure that Megui and staxrip are outputing the exact same AR ?
Do you generally use Gspot and manually correct the AR in Megui?

[jagabo]

Gspot reveals that the video converted with Staxrip and megui have a different DAR than the original video.
The original video is 1.778
The converted videos with staxrip and megui are 1.818
The converted video with Xvid4PSP is 1.778.

The difference is this:

Digital NTSC TV uses a 704x480 frame (704x576 PAL) to represent the 4:3 TV screen. Capture cards usually capture 8 extra pixels at the left and right edges in case the capture is slightly off center. So the full width of the capture , 720x480, is slightly wider than 4:3.

DVDs usually use a 720x480 frame size too. The MPEG 2 spec (the DVD spec refers to the MPEG 2 spec with regards to aspect ratios) says the full frame represents the indicated display aspect ratio, not the 704x480 sub portion.

Some programs go by the digital TV spec, some by the MPEG 2 spec. The difference is the ratio of 720/704:

1.777 * 720 / 704 = 1.818.

[ARTO65]

What is the most accurate way to rip a DVD then ?
The 1.778 or the 1.818 ratio ?

[manono]

What is the most accurate way to rip a DVD then ?
The 1.778 or the 1.818 ratio ?

It depends on whether or not it's using a 704 width (padded out to 720 with black) or a full 720 width. If the full 720 width, then 1.818:1 is more accurate. Not that you'll be able to tell the difference if you resize to 1.778:1. It also depends on how the DVD production company did it (based the 16:9 on the 704 or 720 widths). Unless you want to start measuring circles, there's just no real way to know.

[jagabo]

What is the most accurate way to rip a DVD then ?
The 1.778 or the 1.818 ratio ?

The MPEG 2 spec is clear -- the full 720x480 (720x576) frame constitutes the 4:3 or 16:9 picture. But both methods appear to be in common use. So the answer is: it depends on the individual DVD. The only way to tell is to find something in the movie with a known aspect ratio and measure it. Even then it's hard to tell because the difference is so small.

[ARTO65]

Thank you very much for your answers, it's much clearer now (or not )
I didn't think there was that much room for error.
I also went and educate myself with the ressources I found (seemoredigital, Jukka Aho's guide, etc.).

[jagabo]

In general: DAR = SAR * PAR

https://forum.videohelp.com/threads/322346-same-resolution-but-difference-in-display-w-...=1#post1995959

[ARTO65]

So I tried to measure objects with a virtual ruler (Picpick's) and well... inconclusive...

What are your assumptions when you rip a dvd ? You base your guess on existence of left&right padding ?
Or you always use the same AR ?

[ARTO65]

Actually, I found a ball in a 4:3 DVD and measured it.
With the DAR set at 1.368, the circle is approximately 730x730 pixels.
With the DAR set at 1.333, the circle is approximately 710x730 pixels.

So in this case, the output by Megui and Staxrip seems more accurate.

[jagabo]

I usually just assume the full 720x480 or 720x576 frame is the 4:3 or 16:9 display aspect ratio. That corresponds to 32:27 and 64:45 PAR.

[ARTO65]

If I understand correctly, for 16:9 videos, you use 32:37 PAR for NTSC DVD, 64:45 PAR for PAL DVD.
So, for 4:3 videos, you use 9:8 PAR and 30:32 PAR ?

This means you always assume a DAR of 1.333 and 1.778 for full frame DVDs ?

[jagabo]

If I understand correctly, for 16:9 videos, you use 32:37 PAR for NTSC DVD, 64:45 PAR for PAL DVD.
So, for 4:3 videos, you use 9:8 PAR and 30:32 PAR ?

Sorry, yes. I forgot to give all four PARs.

This means you always assume a DAR of 1.333 and 1.778 for full frame DVDs ?

Yes. I decided on that because that's what the MPEG 2 spec says. Even though some movies appear to use the 704 sub frame.



As you can see there is a mechanism to override that calculation, by using the sequence display extension. But I've never seen that used except to define a 4:3 pan/scan area on a 16:9 disc.

[poisondeathray]

Not trying to confuse you, but the "SAR" used in h.264 is different than the "SAR" used in MPEG2

in MPEG4/AVC/h.264 , "SAR" is sample aspect ratio, or the w:h of the pixels. This is known as "PAR" in MPEG2 or pixel aspect ratio

It's relevant, because you are using x264. You enter the --sar x:y command (there is a checkbox in some gui's as well)

These are the SAR values, based on 704px vs. 720px width

NTSC 4:3 => sar 10:11 (or 8:9)
NTSC 16:9 => sar 40:33 (or 32:27)
PAL 4:3 => sar 12:11 (or 16:15)
PAL 16:9 => sar 16:11 (or 64:45)


It's simple math - so for a PAL 16:9 you would use 16:11 or 64:45

Because for 704 width:
16/9 = 704/576 x 16/11

or for 720 width:
16/9 = 720/576 x 64:45

[ARTO65]

Thanks for the info.
Staxrip is great for displaying and editing that kind of information, listed as PAR and DAR. It uses 40:33, 10:11, 16:11 and 12:11 by default.

So well... I guess I'll roll the dice to decide which method to use.

[manono]

Actually, I found a ball in a 4:3 DVD and measured it.
With the DAR set at 1.368, the circle is approximately 730x730 pixels.
With the DAR set at 1.333, the circle is approximately 710x730 pixels.

So in this case, the output by Megui and Staxrip seems more accurate.

Oh, it's a 4:3 DVD. I do it the same as MeGUI and StaxRip, I guess (never having used either of them). ITU resizing. However, there's maybe something else to consider. If the film is an old classic then 'Academy Ratio' is 1.37:1 and not 1.33:1 as is often thought. Many, but not all, DVD production companies will have the film fill the entire DVD with no black bars on the sides.

[ARTO65]

@manono, What program do you use to rip DVD?
Most of the DVDs I rip are old/rare DVDs, so many of them are completely butchered (interlacing all over the place, 25th extra frame...).

[jagabo]

Also, DVDs made from video tapes are likely to use ITU base aspect ratios.

I rip DVDs with DVDFab, then convert with DgIndex, AviSynth, and x264.

[manono]

@manono, What program do you use to rip DVD?

Rip? As in decrypt to the hard drive? I use DVD Decrypter as most of the DVDs I convert don't have any advanced copy protection. Many have none at all.

[ARTO65]

Rip? As in decrypt to the hard drive?

Yes, excuse me, I wasn't precise enough.
Rip as in the whole process from getting a video on DVD to the final file you keep on your computer.


@jagabo: whow, that's manual!

[manono]

Manual for me also. AviSynth scripts into VDubMod for XviD AVI and into CCE for DVD reencoding.

[jagabo]

@jagabo: whow, that's manual!

Ten minutes to rip a DVD in the background, a few minutes to set up for AviSynth, and an hour to encode in the background.