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The main issue I have here is are the 720P, 480P, 240P... classes for defining video quality or do they unambiguously define the resolution of the video?

For example, the wikipedia article about 240P refers to a family of resolutions.

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    No, as the article you link to talks about aspect ratio, and that determines the horizontal resolution given the vertical one is fixed.
    – CodeCaster
    Dec 17, 2013 at 9:39

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240P, 480P, 720P, etc. give you vertical resolution. However "P" does not stand for "pixels" but for "progressive". 720p means that all 720 lines are drawn in each frame. It is the opposite to Interlaced (denoted as "i") where just half of the lines is drawn each frame.

So the numbers give you vertical resolutions. Horizontal resolution depends on a given aspect ratio.

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    While this is true, you will probably see that most of the time the horizontal resolution is fixed while the vertical one can have different values. For example, in the case of 720p: you will see many movies with resolution 1280x720 (most common), 1280x536, 1280x588, 1280x688 etc. In these cases, even though you don't have 720 vertical lines, these resolutions are still considered to be 720p or 720i.
    – Radu Murzea
    Dec 17, 2013 at 14:07
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    @Radu Considered by whom?
    – Rotem
    Dec 17, 2013 at 15:54
  • By filmmakers. There are many aspect formats inbetween 16:9 and 2.21:1 which are mapped to horizontal resolution (usually 1280 or 1920) which means vertical resolution is smaller than 720 or 1080 (remember those black strips above/below). It all depends on topic we are looking at, physical display properties or video clips or ..
    – Kromster
    Dec 18, 2013 at 12:56
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720P

  • 720 means 720 lines to paint, the image on the screen has this amont of lines.
  • P means full pictures, so every line is painted, to create a image on the screen.

If you have a 100Hz device, the device paints 100 full pictures in 1 second. All 720 lines are painted each turn.

You can not find out the resolution by this information.

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The main issue I have here is are the 720P, 480P, 240P... classes for defining video quality or do they unambiguously define the resolution of the video?

If you have a video file, and all you know is that it's 1080p then it's safe to assume it's 1920x1080. The 1080p and 720p formats are often 16:9 aspect ratio.

If you have a video file, and all you know is that it's 480p then it's safe to assume it's 720x480. The 480p formats are often 4:3 aspect ratio.

While it's true that 1080p only tells you scan lines you can assume the video resolution if the context is that of a regular video file.

There are exceptions. NetFlix uses HD Video but it's shown at 720p which isn't true HD. So later they came out with UltraHD which is 1080p. Still, the video compression is high so the quality is low.

Samsung has released new TVs that display UltraHD which is 4320p at 16:9.

Unless resolution is explicitly stated it's difficult to always know exactly what it is. One trick is to divide by 45. If you get an remainder then it's 4:3 and if no remainder it's 16:9. 

 4320 / 45 = 96 (16:9)
 1080 / 45 = 24 (16:9)
 720 / 45 = 16 (16:9)
 480 / 45 = 10.6666 (4:3)
 240 / 45 = 5.3333 (4:3)
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    I assume you mean 4:3 not 4:9.
    – Gort the Robot
    Dec 18, 2013 at 5:15
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This needs clarifying. Clime is correct in this answer. The P in 1080p 720p refers to 'progressive'. It means that the image is intended to be render its lines to screen one line at a time, sequentially.

This comes from the old days where TV was a cathode-ray tube device that needed to render images in an interlaced manner to improve the temporal appearance to the viewer -- start at the top, then emit the even lines first then return to the top then the odd lines odd lines. The set of lines that is half a picture it called a 'field' and a full image is made up of two interlaced fields. We refer to these formats as 1080i, 720i.

To get the spatial resolution you must look beyond the name of the format because, as you've found, they are as best ambiguous. The info you need is in the file's header as metadata.

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It is not safe to assume the horizontal resolution. My camera (Sony Nex6) films 1080P. However, it records AVCHD using 1980x1080 using square pixels and MP4 at 1440x1080 using rectangular pixels.

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