Illustrator video rulers measurement explained

[SirRoadDog]

When creating a lower third in Illustrator, I select New > Film & Video > HDV/HDTV 1080 (1920 x 1080 px). This provides a blank artboard with the green video rulers and center mark, cross hairs and video safe area boxes from the Video and Film profile (as expected). 

The right side vertical ruler shows a maximum marking of 1080 (as expected), but the top horizontal ruler shows a maximum marking of 1440 (not expected; this was expected to be 1920). I verified that I had selected the correct template by creating a normal rectangle to dimensions 1920 x 1080 and placing it inside the video frame, which it filled entirely (as expected).

My question is: what is the horizontal video ruler measuring that a 1920x1080 video frame measures 1440 px wide? Even more confusing, when I create a blank document using New > Film & Video > HDV 720 (1280 x 720 px) and New > Film & Video > 4K UHD (3840 x 2160 px), the horizontal and vertical video rulers show the measurements expected. It's just the horizontal video ruler for 1920x1080 that shows a different horizontal measurement of 1440. Is this just a bug?

[Monika Gause]

Does the ruler start at 0 on the left side?

[SirRoadDog]

Yes.

[Monika Gause]

Can you open the artboard options and check the pixel aspect ratio?

[SirRoadDog]

Yes, you are correct. The default value for the Video Ruler Pixel Aspect Ratio for New > Film & Video > HDV/HDTV 1080 (1920 x 1080 px) is 1.3333. If I change this to 1.0 then the horizontal ruler displays 1920 as expected.

This raises a few questions. 

1.) The default Video Ruler Pixel Aspect Ratio for both HDV 720 (1280 x 720 px) and 4K UHD (3840 x 2160 px) is 1.0, but for HDV/HDTV 1080 (1920 x 1080 px) it is 1.3333. Why would these be different?

2.) What is the value of changing this setting? If I am looking for a 1920x1080 screen resolution, what benefit is gained by measuring the horizontal pixels to only 1440?

[Monika Gause]

These settings are for video and have been introduced a couple of years ago. I'm not very versed in video specifications or the role of aspect ratio in them today. 

[Mylenium]

This harkens back to the legacy HDCAM format, which actually only was 144o pixels wide and the output was scaled to full HD on decoding. I'm sure it's still somewhere in the official ITU specs.

Mylenium

[Ton Frederiks]

I am sure someone at the After Effects or Premiere Pro forums can help you with this question.

 https://community.adobe.com/t5/after-effects/ct-p/ct-after-effects

https://community.adobe.com/t5/premiere-pro/ct-p/ct-premiere-pro