When converting footage with non-sqaure pixels (like, say, DV or D1) for viewing on a computer monitor (so to 640x480) how do I handle pixel aspect ratio?
In Episode, for example, I can use the "resize" filter and have options to maintain proportions by "Cut", "None (Distort)", or "Letterbox(Pad)". It seems to me that none(Distort) would make the most sens in this case (going non-square to sqaure) but I wanted to check. Thanks for any info.
Thanks, Brian. That was what I thought but the documentation was a little confusing - mostly just because they mention specifically anamorphic MPEG-2 but nothing else. I was trusting my eye but wanted make sure I was technically correct.
Could someone also explain formats that have a "display" aspect ratio? Like for example, if I have an MPEG-2 file at 720x480 for DVD - so non-square pixels - when play it in Quicktime player it shows up at the proper computer display of 640x480. Is this a function of quicktime being smart and knowing that 720x480 almost always means 640x480 for a computer display, or is it built in to the file somewhere as a "display" aspect ratio for use on computer?
Agreed, Telestream need to improve the explanations for this filter.
[Scott Bush]" when play it in Quicktime player it shows up at the proper computer display of 640x480. Is this a function of quicktime being smart and knowing that 720x480 almost always means 640x480 for a computer display, or is it built in to the file somewhere as a "display" aspect ratio for use on computer? "
Quicktime is smart, but not all the time.
There are no significant bugs in our released software that any significant number of users want fixed. … I'm saying we don't do a new version to fix bugs. We don't. Not enough people would buy it. You can take a hundred people using Microsoft Word. Call them up and say "Would you buy a new version because of bugs?" You won't get a single person to say they'd buy a new version because of bugs. We'd never be able to sell a release on that basis.
Bill Gates. Focus Magazine No. 43 (23 October 1995)
Not all pixels (picture elements) are created equal. Most modern computer and TV displays, DLP, Plasma, LCD, and LCoS, use square pixels to re-create images from an analog or digital video signal.
Video imagers, CCD and CMOS, do not always the same square pixel formats as displays. Sometimes they use odd (not normal) pixel counts on the imaging chips then process the image to create a standard size video frame. When this happens the video is tagged with a 'flag' to tell the computer, monitor, or equipment how to display the image.
The aspect ratio flag is part of the ancillary data and is represented by a 4 bit code word. Unfortunately a lot of times this flag is lost in the processing of the video signal. Quicktime does not always recognize this flag (probably because it is not present).
It's best to output assuming square pixels. If your video is distorted in QuickTime you may have to manually type in the correct pixel count (based on square pixels) to view your video distortion free. This is especially true when looking at 720 x 480 16:9 video in quicktime. Sony DVCAM products do not add this flag so the video will look squeezed horizontally or stretched vertically so manual input is a necessity to view the video distortion free.
This all makes sense to me, but of course I can't tell my client to "just type in the proper aspect ratio" it just needs to work for them, distortion free. I never send them DV footage anyway so I'll be making sure the pixels are correct in what I send them - but this helps me understand it better. Many thanks.