[whatwg] Video source selection based on quality (was: <video> feedback)

David Singer singer at apple.com
Mon Feb 15 17:09:49 PST 2010

I think I agree with Tim here.  When you ask to watch "360p" content, you are asking for content that has 360 lines of pixels to be displayed to you.  You're not asking for whatever is displayed to you to occupy only 360 lines of pixels on your display. Yes, when it is shown larger, then filtering etc. is done to avoid pixel-doubling blocky artifacts;  this does not increase (and, we hope, not decrease) the amount of information in the scene.

With the advent of higher-resolution displays, and the ability to use CSS with HTML to set 'sensible' sizes of video relative to other page content, the assumption that video will always be displayed in a 1:1 ratio of source (coded, transmitted) pixel to display pixel is increasingly untenable.

On Feb 15, 2010, at 17:03 , Hugh Guiney wrote:

> On Mon, Feb 15, 2010 at 7:07 PM, Tim Hutt <tdhutt at gmail.com> wrote:
>> Erm, what? The 360p refers to the 'native' resolution of the video
>> file youtube sends. If you play a 360p video fullscreen, it's still
>> only got 360 lines; they're just scaled up. It would be meaningless if
>> the number referred to the final playback size since that is
>> independent of the video quality.
> By "lines", do you mean TV (or scan) lines?
> TV lines and pixels can both be used to describe image resolution, but
> they aren't the same thing. The difference is very technical and isn't
> relevant to this conversation but essentially, TV lines pertain to
> analog systems and pixels pertain to digital systems. And in the
> digital realm, magnification is achieved through interpolation: since
> the source image has less pixels than the destination image, a
> resizing algorithm must invent pixels to fill in all of the unknown
> values in the target image, based on the known values in the source
> image. The result is a "best guess" of what the image might look like
> at that resolution. The pixel count has changed; it is therefore new
> data and not the same as the input.
> The way YouTube has it now is meaningless since the player doesn't
> expand when you change the height (that's what that number is supposed
> to indicate). The older standard/HQ/HD made more sense.

David Singer
Multimedia and Software Standards, Apple Inc.

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