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I've got a video and I thought it's size was 640x480 and this is shown on GSpot.

However also in the container section of GSpot it is saying

 Recommended Display Size: 853 x 480

does anyone know where it get's this from?

1) If it is calculated what from?

2) If it is a property of the file while isn't it the same as the width x height?

GSpot Example

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2 Answers 2

I don't know what tags or fields are present in a .MP4 file, but something is flagging the file as having a 16:9 'display aspect ratio' (shown as "dar" in GSpot), while the 'pixel aspect ratio' (par) is 4:3.

((480 * 16) / 9) = 853

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480 is the original height? Multiplied by the dar ratio width, divided by the dar ratio height = 853 new width? Seems an odd calculation –  Blundell Jan 13 '13 at 1:15
    
BTW 16:9 is correct, so is it the 'par' that needs updating and this would correct the original WxH? –  Blundell Jan 13 '13 at 1:20
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Not all video formats use square pixels. In this case, the pixel's are oval (anamorphic wide screen). This comes indirectly from the film days when anamorphic lenses would condense a wide screen image on to a narrower strip of film. The same concept was later applied to squeeze wide screen videos in to video formats that wouldn't normally support them. The playback would occur at a normal resolution, but then the display could scale it out to make the proper aspect ratio.

There may only be 640 by 480 pixels in the video (standard definition 4 by 3 video with square pixels) but since it is widescreen, each pixel represents a wider area. The recommended display resolution is determined by resolving how that would map to actual square pixels based on the width of each of the 640 columns of pixel data.

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