Why Virtualdub captures in 5:4 aspect ratio with Elgato?
 

Hello everyone,

I've been reading many posts on this forum. And I find this a great platform for video related queries.

This will be my first time posting a thread here.

I live in The Netherlands. Due to the corona crisis time I have taken the opportunity to digitize my old VHS movies. Yesterday I received the Elgato analog video capture device. At first I thought maybe it is a bad buy. But then I followed some guides on this forum to use Virtualdub for capturing. Video compression in Lagarith and audio uncompressed.

I find the capture and quality very satisfactory.

However when I check the AVI file with MediaInfo, It states almost everything is fine according to PAL system. FPS is 25. The bit rate is as expected high due to lossless compression Lagarith.

But why does it state the aspect ratio is 5:4

Shouldn't it be in 4:3 ?

Can anyone enlighten me the theoretical background of this? I am just curious.

I think your confusing Storage Aspect Ratio (SAR) with Display Aspect Ratio (DAR)

Wikipedia has an article on this: Pixel Aspect Ratio

"simplified" elaboration: In the digital world (in a storage context) all pixels are created equal, they are square. In the display world (formerly the analog world) pixels can be anamorphic or "any shape" they want, usually rectangular. The Aspect Ratio is a malleable term and can be interpreted in programs when it is listed as a value in a menu or report. They don't necessarily tell you "which" Aspect Ratio they are referring to, SAR, DAR or PAR.. they just say "Aspect Ratio"

.. and that leads to confusion.

The mediainfo of the file reports the following:

kindly see the attached txt file.
it says the display aspect ratio of the captured avi file is 5:4


Should I pay attention to this? Or can I continue to import the file in Premiere pro for eventual editing and exporting as H.264 mp4 file?

Neither the video format (lagarith), nor the container (.avi) supports specifying an aspect ratio. This means the only info mediainfo has to go by is the video resolution, and thus assumes the ratio is simply 720:576 to 5:4. What you actually get from the capture card is 4:3 video that's squeezed vertically to be 720 pixels wide. The .avi format is a bit antiquated, but it's the only thing virtualdub can save to when capturing. If you are importing it into premiere, you will have to inform it in some way that it is in fact 4:3, and interlaced with the top field first (also not info stored in the file).

Both the mp4 container and the h.264 format supports specifying info about aspect ratio, so it can either be set when eventually exporting to that format, or alternatively maybe premiere will resize it or something if it can be specified when importing.

Thanks for the explanation. Premiere pro does somehow specify it as 4:3 when imported.

Still one question arises. Few days ago I was importing MiniDV tapes through firewire with WinDV program.

When I opened those AVI files with MediaInfo. They contain the following information. Kindly see the attached file.

How come that AVI file contains all info regarding aspect ratio and interlacing?

Media info treats the pixels as square but in reality the are not, they are rectangle. So you will have to assign a pixel aspect ratio flag when you encode to the final format. However the 720x576 resolution represent more than just the active video area, 16 black pixels were added horizontally by the capture card on each side (you can look up the reason for this). So if you give 720x576 a 3:4 aspect ratio the video will be squeezed horizontally by 16 pixels, The right way to do it is to trim off those 16 pixels using crop tool in vdub to 704x576 (sometimes you trim more on one edge than the other depends on the black area thickness) and set the pixel aspect ratio to 12/11, You will get a perfect 4:3 clean video frame.

Digital formats such as DV, D8 and DVD use the whole 720x576 as an active video area and the format already contains a pixel aspect ratio flag, just to note the difference from analog sources.

Thank you all for your kind replies.


But I have already returned the Elgato, because I was not satisfied with the audio results.

Very interesting and well explained, Hodgey!

I will throw a spanner in the works and say that my no-name Phillips PCI card will capture 768x576 into Lags with V Dub! Much nicer to look at, a "proper" 4:3 capture window...

I'm not aware of any capture card that capture natively in 768x576, Unless you are resizing on the fly.

Here you go, Latreche. I merely set the capture format to 768x576 (which VDub accepted; if I'm using my VGB-100 card, it won't accept 768x, only 720x). I can see the monitor change size when I choose 768x576. I'm not aware of any resizing: I just hit Capture and this is what I get.

I've come across some capture cards that vdub or similar programs gave several options of resolutions, But the actual native resolution should be found in the chipset specification document from the chip manufacturer. Post the ADC chip numbers here so we can take a look. I'm not saying it's impossible, it's just out of spec resolution for the ITU-R 601 (orig. CCIR-601) standard aka Rec. 601.

Don't know how to get the ADC chip numbers but this is how Device Manager sees it, as per the attached. It's the Phillips entry.

No, The ADC chip model will not be listed in Windows device manager, The whole card model will be listed, You'd actually have to remove the card and look at the ADC chip markings if interested.

Rojer doger, I won't be doing that anytime soon! It's working well so I might let sleeping dogs lie. :D

I suppose the question is, is 768x576 4:3 better quality (more pixels) than 720x576 4:3 for say viewing on YT or my TV?

According to this datasheet it is conform to ITU-R 601 sample rate, So it is 720 native, I'm starting to think it is built in MPEG-2 hardware chip, which explains why Vdub giving you the option to convert from mpeg-2 to any format at any resolution. hmm .. worth investigating.

Thanks Latreche.

Here is your sample properly cropped then resized to 720x576 for compatibility purposes, de-interlaced and encoded to H.264:

Thanks LaTreche, that looks pretty good. As LS says, "better than the original".

I'm still trying to get my head around this aspect ratio stuff, but will post any more questions/thoughts on a more appropriate thread.

Just remember this: never use that mantra as an excuse to accept mediocrity.
Use it as intended: to reflect the best effort possible; to avoid going down a rabbit hole of unobtainable perfection.

And it needs work to be better quality, but see attached... :)

Crikey! That's even "more" better than the original! :eek:

I have 20 hours of this stuff. Could I send it to you?! :D

I had better do some more work...