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1) How does video player (software) play video when "frame width = 720px" and "frame height = 400px" while the display resolution is set to 1920x1080 (I don't see any top and/or bottom black bars)?

2) How does it do that when frame resolution is larger than the display resolution?

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up vote 3 down vote accepted

The 1920 x 1080 resolution display is a good match for 720 x 400 resolution video to maintain the aspect ratio because:

  • 1920 divided by 720 = 2.666666666667...
  • 1080 divided by 400 = 2.7

Since the results of that quick math yield such close results, any black bars that would normally show up to fill the void on different resolutions will likely be so thin that they'll just blend in with the outside of the viewable screen area.

What I suspect is happening is that your video player software is increasing the size of your video by 2.666666666667 pixels (or something very close to this) on both the horizontal and vertical aspects, and just leaving the small difference black, which is not really noticeable (and certainly less noticeable than stretching to fit the entire screen without maintaining the aspect ratio because then some things will look oddly, yet very subtly stretched).

An easy way to test this out is to switch out of full screen mode with your video player software, and see if the thin black edges do show up between the GUI borders of the video player window and the video itself. Usually Alt-Enter is the keystroke to use to switch in and out of full screen mode -- if not with your software, then try VLC Player as I believe it does have this feature:

  VLC Media Player (free, and open source)

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I use VLC Media Player. When i go to Tools->Codec Information... i see Resolution 720x400, Monitor Resolution (also!!) 720x400 but my actual monitor resolution is 1920x1080.. How come?? – DrStrangeLove May 9 '11 at 20:46
720x400 is the total size, in pixels, of the media (in this case the video) that you're playing. 1920x1080 is the total size, in pixels, of your screen. VLC Media Player will stretch the video image to fit your screen. Why the video is 720x400 is something that only it's producer can answer. Why your monitor is 1920x1080 has to do with how your OS is configured (this could be due to your choice, or, more likely, as a result of your OS automatically detecting the optimal screen size and defaulting to that). – Randolf Richardson May 9 '11 at 23:02
Those pixels are organized in a grid, just like a piece of graph paper but with very tiny squares. Your screen is made up of a grid of pixels, and so is your video. If one pixel of your video can fit into four pixels (2 wide and 2 high) on your screen, then the stretching operation would be straight forward because for every four pixels (in a 2x2 formation) it will draw one pixel from your video, resulting in a larger image. When it isn't a perfect fit though, then "anti-aliasing" and similar techniques are used to stretch the image while retaining as much quality as possible. – Randolf Richardson May 9 '11 at 23:05
Thanks a lot!! :) – DrStrangeLove May 10 '11 at 0:06
@DrStrangeLove: You're welcome. I'm glad that was helpful to you. – Randolf Richardson May 10 '11 at 4:14

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