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Author Topic: Help to understand meaning of video resolution numbers  (Read 5729 times)
Robert Roaldi
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« on: March 27, 2009, 08:06:18 AM »
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I would like to understand video specs better. I have been through the article on LL regarding the differences between HD, SD, etc., and I understand the basics but think I need to read more detail. It would help if someone could point me to a comprehensive primer (online or not). To me, video resolution numbers don't seem to mean the same thing that they do in still photography. It is as though they are "nominal" numbers or maybe they imply more than the resolution of a single frame taken as a still.

This is what is puzzling me at the moment. I shot a video on a SD camcorder, using the 16:9 wide screen option. Uploading and editing in iMovie9 went well. I then became confused when uploading to vimeo. I tried numerous size conversion options trying to understand when the vimeo reprocessing (after upload) would add black bars, but I could not detect a pattern. I then read through the vimeo forums and someone very helpful there had written that exporting in QuickTime using custom size 872 x 480 worked best for SD widescreen in vimeo. (Btw, I tried uploading various sizes of exported snippets to YouTube to figure out what worked best there, and never really found anything that worked well, but I gave up early.)

I don't understand why 872 x 480. It is not exactly 16 x 9, although sort of close. When I uploaded at a custom ratio of 16 x 9, I would get black bars. Is it just because SD widescreen is NOT 16 x 9?  (Why wouldn't it be, since I presume it was invented to cater to widescreen TVs?)

Like I said, if you know of a comprehensive document  that explains this stuff, that would be perfect. Thanks very much.
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Andrew Fee
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« Reply #1 on: March 27, 2009, 01:04:07 PM »
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Standard definition video is either 720x480 @ 60Hz (NTSC) or 720x576 @ 50Hz. (PAL)

If you have a widescreen standard definition image, it still has one of those two native resolutions, but it is anamorphic which means that it uses non-square pixels that are stretched out by the display to the correct aspect ratio. So you have 720x480 stretched out to 854x480, for example.


You also have interlaced/progressive to deal with. An interlaced image means that each frame is broken into odd/even lines. So 480i is actually sixty 720x240 resolution images per second.

This can either be used to capture 60 unique, but low resolution images— 720x240 @ 60fps, or it may be storing 60 half-images that have to be recombined at the display for 720x480 @ 30fps.

Progressive recording means that the full 720x480 is captured and stored, which means you can have both the high framerate and high resolution at the same time— 720x480 @ 60 fps.


High definition formats are: 720p, 1080i and 1080p. All of these are native 16:9 resolutions.
720p is 1280x720
1080i is 1920x1080 (but stored as 1920x540 fields)
1080p is 1920x1080

That said, not all cameras that capture these formats do so at full resolution. There are some 1080i cameras that record at 1440x1080, for example.

I hope that helps.


EDIT: Oh, and your monitor is almost certainly 16:10, so even if you use the correct 16:9 aspect ratio for your video, watching it fullscreen will give you black bars top and bottom. (perhaps that was the problem?)
« Last Edit: March 27, 2009, 01:09:47 PM by Andrew Fee » Logged
Robert Roaldi
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« Reply #2 on: March 29, 2009, 08:41:33 AM »
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Thank you Andrew. The black bars that I was referring to are not on my monitor but on the display window of vimeo (and YouTube).

It is the "anamorphic" angle that throws me. I simply don't know enough about broadcast standards (especially analogue ones). And why I need to export as 872x480 rather than  854x480 is still confusing, but that's a problem for another day.
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