Why does QuickTime report a different resolution?
Ever wondered why QuickTime reports a completely different resolution to the one you exported at?
Welcome to the world of non-square pixels. NTSC and PAL use rectangular pixels to fill up space on the screen and save transmission bandwidth, which was more of an issue when the standards were invented. Computer monitors use square pixels and so QuickTime has to squeeze one side of the image in order to prevent it looking stretched. This is purely for display and the file is not modified.
The pixel aspect ratio of NTSC footage is 0.889 meaning 720 x 0.889 = 640 so it is displayed at 640x480. For PAL it is 1.067 so 720 x 1.067 = 768 and it is displayed at 768x576.
QuickTime also has some options for controlling how the movie is displayed. Open up your movie, go to Window > Show Movie Properties
and click on the Presentation tab.
You will see an option marked "Conform aperture to:" with the following options:Classic
- Classic is identical to having the conform aperture setting switched off.
- Scales the image to compensate for the pixel aspect ratio and crops it to mimic the overscan on a broadcast monitor.
- Scales the image to compensate for the pixel aspect ratio but does not crop the image.
- No modification is made to the footage. Note the stretching caused by non-square pixels.
This is one of the many reasons why a broadcast monitor is essential.
Posted by Jon Chappell on Sunday April 13 2008 3:02 AM to Video Editing, Analysis, QuickTime
Post ID: 243