VHS video capture aspect ratio

[Dave Reid]

I made a simple test following discussion on a previous thread (VHS video capture quality less than TV quality) regarding capture size to retain correct aspect ratio using a Phillips SAA7133/7134 chip capture card. And here are the results which are a little bit puzzling + I wonder if someone with more video experience than me (complete novice here) can make more sense of them.

The test I conducted was to video (using a Panasonic VZ10 VHS-C camera) a square subject. Then captured the video at both 704x576 and 720x576 resolution using VirtualVCR, compressed to mpeg2 using TMPGEnc (full screen, keep AR; video arrange method) and creating a DVD using Roxio Creator 6.
I then measure the width and height of the square object as displayed on screen for both original video and captured DVD video. I calculated an aspect ratio distortion as follows.

100*Width/Height (if there is no distortion of the aspect ratio this should be 100)

Below is the result of display of the object in various formats.

ANALOGUE VIDEO
98.3 LCD display on camera (very close to square + difficult to measure accurately due to small screen size ie only 1.5mm difference between height and width)
104.6 Camera connected to TV via composite video cable
104.6 VCR connected to TV via antennae connection

CAPUTURED DVD VIDEO
103.2 704x576 DVD on TV
106.5 720x576 DVD on TV
102.5 704x576 DVD on PC using Intervideo WinDVD
105 720x576 DVD on PC using Intervideo WinDVD

I guess it shows that the 704x576 capture is giving a result that is closest to the correct AR.

It is interesting to see that there is variability in the AR depending on what it is played on (ie TV vs PC) + also in the Camera vs VCR TV display. Maybe I need to check the settings on my TV?

[Wilbert]

I guess it shows that the 704x576 capture is giving a result that is closest to the correct AR.

True. It all the depend on the capture window of your capture card/driver. The one of Phillips SAA7133/7134 chip is 52.15 µs, which equates 704 dvd pixels.

http://www.doom9.org/capture/sizes_advanced.html