[whatwg] Video source selection based on quality (was: <video> feedback)
hugh.guiney at gmail.com
Mon Feb 15 17:03:36 PST 2010
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.
More information about the whatwg