Video Aspect Ratio vs. Display Aspect Ratio

[goddi]

Greetings,

I am not sure what the difference is between ‘Aspect Ratio (AR)’ and ‘Display Aspect Ratio (DAR)’ for a video clip (as shown in MediaInfo).

I started out with the original video clip’s AR being 720x480 and a DAR of 4:3.

I ran the original through PTE Convert/Trim and the properties remained the same, 720x480, 4:3.

I also ran the original clip through Hitfilm video editing program to trim it but the clip came out as 720x480, 3:2 (not 4:3 as expected).

The 4:3 DAR seems to look correct while the 3:2 seems to be ‘stretched’ out a bit.

Mathematically, it seems that if the AR is 720x480, the DAR should be 3:2, not 4:3. But the 4:3 seems to be visually correct and not stretched out.

If the original clip’s AR is 720x480 and the DAR is 4:3, why would Hitfilm change the DAR to 3:2? The Hitfilm’s export preset was set to use the same Dimensions and Aspect Ratio as the source.

And what is the difference between the AR and DAR? Should a 720x480 be 4:3 or 3:2?

Though PTE keeps it at720x480, 4:3, Hitfilm changes it to 720x480, 3:2. Can you tell me why?

Gary

[Picsel]

Hello Gary,

I hope I understand correctly your problem but...

With PTE the Aspect ratio is the aspect ratio of the screen (slides). You can choose an aspect ratio of 4:3 for the screen and put on it your  photos or videos which have their own format (in your post video clips 720x480 => 3:2 so in this cas you will get two black (depending on the color selected) stripes above and below. When you create your video take care that pan scan should be disabled in order to keep the same aspect ratio.

Daniel

[goddi]

3 hours ago, Picsel said:

Hello Gary,

I hope I understand correctly your problem but...

With PTE the Aspect ratio is the aspect ratio of the screen (slides). You can choose an aspect ratio of 4:3 for the screen and put on it your  photos or videos which have their own format (in your post video clips 720x480 => 3:2 so in this cas you will get two black (depending on the color selected) stripes above and below. When you create your video take care that pan scan should be disabled in order to keep the same aspect ratio.

Daniel

Greetings Daniel,

I've fiddle around a bit more with this question. I do understand, as you explained, about selecting the the aspect ratio of the screen (slides) in PTE. However, let me explain a bit more.

I notice that the Aspect Ratio (AR) and the Display Aspect Ratio (DAR) of video clips taken with a digital camera seem to make sense. They match up. For example, a 1920x1080 will show a DAR of 16:9 (1.77). And, 1280x720 will show a DAR of 16:9 (1.77). And, 640x480 will show a DAR of 4:3 (1.33). (using MediaInfo for the properties).

Now, I am working with video clips that  I took with a HI8 tape camera and were digitized. What is strange to me is that these 720x480 clips show a DAR of 4:3 (1.33). I would think the DAR should be 1.5, to be mathematically correct. Even when these clips are PTE Converted, these 720x480 clips show a DAR of 4:3 (1.33).

OK. So, then I run this digitized HI8 clips through another video program called HitFilm to trim and export (just trying out a new program). I would expect MediaInfo to show the same results. However, it show 720x480 and a DAR of 3:2 (1.5), which is really the correct info.

So, I am wondering why, with the HI8 digitized clips, the 'incorrect' DAR is shown, even with the  PTE Convert process. Not until I played around with HitFilm did the DAR show up 'correctly'.

I am not sure what the ultimate effect of using the PTE's DAR 4:3 vs. the 3:2 that HitFilm shows of trimmed clips. Does it even matter??? However, I notice if I set the Aspect Crop in PTE's O&A to 3:2, the clip's width looks stretched. Apparently, the clip actually is 4:3? Just curious why I'd  get two different DARs of the same clip.

Gary

 

 

[Picsel]

Gary,

your explanation sounds for me like if there was a problem of pixel format. If your Hi8 camera uses an anamorphic format, the pixels could be rectangular and not square. If the PTE converter does not take into account this type of "anamorphic" format that could perhaps explain your problem.

In fact there are two ways to produce digital video clips with cameras. One common way uses square pixels and, depending on the camera possibilities, the other uses rectangular pixels (sometimes it is called "anamorphic" format).  Depending on the rectangular/square ratio it was possible to be able to provide 3:2 video clips or 16/9 videos clips with the same coding 4:3 format using square pixels. So depending on the way the video clip is read by the decoder that could provide (wrong way : without extension of square to rectangular pixels and so the length proportion is distorted ) = 4:3 video clips or (right way with extension of square to rectangular pixels) = 3:2 in the case of your video clips.

So it seeems that in the case of your video clip, PTE does not convert the coded square pixel into decoded rectangular ones. Why?

Daniel

[goddi]

Greetings Daniel,

Your explanation is very interesting. I had never heard of rectangular or square pixels in video. I just when back into the HitFilm program and I see that I can set the Project Settings to change the default Aspect Ratio from 'Square Pixels' to 'Anamorphic'. Maybe this is what is needed to change if I am using the digitized clips from my HI8 camera. I'll have to play around with it some more to see what happens if I select that setting. So, perhaps if I select the 'Anamorphic' in HitFilm and export the clip, the DAR would be 4:3 (as is the original clip), and not 3:2.

I'll give it a test later and let you know.

Thanks... Gary

[goddi]

Daniel,

I just gave it a try. I set the initial Project Setting to 'Anamorphic'. But when I tried to set the Export Presets to be 'Anamorphic', that choice did not show up in the settings list. So I will just live with the differences and fix it in PTE to whatever looks the best. But interesting discussion.

Thanks... Gary