In the event you opened up the ol’ Home windows Media participant again within the 95, 98 or XP days, brace your self for a light shock: it was mendacity to you.
And by mendacity, effectively, what I actually imply is rendering video someplace aside from contained in the precise window that was open in your desktop—type of a parallel airplane of existence to the desktop you had been really —earlier than sneakily porting it over.
In the event you’ve watched a single Twitch stream or Marvel film up to now 15 years, you are most likely all too conversant in the idea of a inexperienced display, a brilliant, single-color floor that makes it straightforward to clean out a background and fill it in with one thing else. A Hawaiian seaside, a bunch of CGI superheroes punching one another, and so forth. The extra correct color-agnostic time period for the method is chroma-keying, which is definitely how Home windows rendered all of its video again within the previous days.
Greatest picks for you
“The media participant program did not render the video pixels to the display,” longtime Microsoft developer Raymond Chen wrote not too long ago in a weblog publish. As an alternative, Home windows would render a inexperienced display (or a unique shade, relying on the model), then “render the video pixels to a graphics floor shared with the graphics card.” The ultimate step was to “inform the graphics card that at any time when it sees a inexperienced pixel about to be written to the display, it ought to substitute a pixel from that shared graphics floor.”
The graphics surfaces had been normally known as overlays as a result of they’d (invisibly) overlay the desktop (that’ll come into play shortly). Chen stated that the method offered a pair benefits: avoiding pixel format conversions if the video format differed from that of the consumer’s monitor, and conserving efficiency regular by decoupling that graphics floor from the method thread that ruled the UI. So even when the Home windows shell had been to hold for a second, the video may preserve enjoying easily.
A extra superior method, referred to as flipping, would play up this efficiency benefit with two shared graphics surfaces, one with the “present” video body and one with the “subsequent” video body, which the video card would change between throughout very vertical clean (because the display refreshed).
This previous video playback method is not very fascinating till we arrive at how you can both deliberately or inadvertently journey up how Home windows was utilizing chroma-keying, as Chen defined:
“Once you took a display shot, you bought the pixels that Home windows gave to the video card because the contents of the desktop. If an overlay is energetic, then these will not be the identical pixels that got here out of the video card and despatched to your monitor. The pc by no means sees these monitor pixels; they’re one thing generated on the fly by the graphics card and despatched on to the monitor. Your display shot was a display shot of the desktop display, and it comprises inexperienced pixels the place the video would go.
“Now, whenever you load the picture into Paint or some other picture viewer, Home windows sends these inexperienced pixels to the video card, but when the media participant continues to be working, then its overlay continues to be energetic, and in case you put Paint in the identical place that the media participant window is, then the inexperienced pixels in Paint get turned into the pixels of the energetic video. The video card doesn’t know that the pixels got here from Paint. Its job is to search for inexperienced pixels in a sure area of the display and alter them into the pixels from the shared floor.
“In the event you transfer the Paint window to a different place the place it doesn’t overlap the media participant, or if the media participant isn’t enjoying a video, you will note the bitmap’s true nature: It is only a bunch of inexperienced pixels.”
Rendering video was once fairly a demanding process for computer systems, however lately there isn’t any want for these types of methods that allowed Home windows to play a tiny 240p file mpeg at 60 frames per second. I do know it is for the higher, however personally I am slightly unhappy that Microsoft Paint is sensible sufficient now to do background removing and even save layers like Photoshop. Computer systems are simply extra enjoyable when you possibly can trick them.
