Video overlay is any technique used to display a video

Video

Video is the technology of electronically capturing, recording, processing, storing, transmitting, and reconstructing a sequence of still images representing scenes in motion.- History :...

 window on a computer display while bypassing the chain of CPU

Central processing unit

The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...

 -> graphics card

Video card

A video card, Graphics Card, or Graphics adapter is an expansion card which generates output images to a display. Most video cards offer various functions such as accelerated rendering of 3D scenes and 2D graphics, MPEG-2/MPEG-4 decoding, TV output, or the ability to connect multiple monitors...

 -> computer monitor. This is done in order to speed up the video display, and it is commonly used, for example, by TV tuner card

TV tuner card

A TV tuner card is a kind of television tuner that allows television signals to be received by a computer. Most TV tuners also function as video capture cards, allowing them to record television programs onto a hard disk much like the Tivo digital video recorder does.-Variants: The interfaces for...

s and early 3D graphics accelerator cards. The term is also used to describe the annotation or inclusion of interactivity on online videos, such as overlay advertising (mid-roll overlay).

Various methods to achieve video overlay are in use:

• A video overlay device can be connected between the graphics card analog VGA
  Video Graphics Array
  Video Graphics Array refers specifically to the display hardware first introduced with the IBM PS/2 line of computers in 1987, but through its widespread adoption has also come to mean either an analog computer display standard, the 15-pin D-subminiature VGA connector or the 640×480 resolution...
  
   output and the monitor's input forming a "VGA passthrough". The device modifies the VGA signal and inserts the analog video signal overlay into the picture; the rest of the screen is filled by the signal coming from the graphics card. The driver software informs the video overlay device about the desired position of the video window on screen. Because of the much greater processing power of modern graphics cards, and the awkwardness of adding additional analog hardware signal processing path, this method is now little used.

• Some video overlay devices write the digital video signal directly into the graphics card's video memory
  Video memory
  Video memory is a term generally used in computers to describe some form of writable memory, usually RAM, dedicated to the purpose of holding the information necessary for a graphics card to drive a display device...
  
   or provide it to the graphics card's RAMDAC
  RAMDAC
  Random Access Memory Digital-to-Analog Converter is a combination of three fast DACs with a small SRAM used in computer graphics display adapters to store the color palette and to generate the analog signals to drive a color monitor...
  
  .

• Hardware overlay
  Hardware overlay
  In computing, hardware overlay, a type of video overlay, provides a method of rendering an image to a display screen with a dedicated memory buffer inside computer video hardware. The technique aims to improve the display of a fast-moving video image — such as a computer game, a DVD, or the signal...
  
   is a technique implemented by most modern graphics cards that allows an application to write to a dedicated part of video memory, rather than to the part shared by all applications. In this way, clipping
  Clipping (computer graphics)
  Any procedure which identifies that portion of a picture which is either inside or outside a picture is referred to as a clipping algorithm or clipping.The region against which an object is to be clipped is called clipping window.-Examples:...
  
  , moving and scaling of the image can be performed by the graphics hardware rather than by the CPU in software. Some solid state video recording systems now include a hardware overlay, which uses dedicated video processing hardware built into the main processor (for example the Texas DM355) to combine each frame of video with an area of memory configured as a frame buffer which is used to store the graphics.

• Overlay advertising is a technique used by online video producers to monetize video content through using an overlay layer to deliver and display an ad unit. This can be in the form of a video advertisement, hypervideo
  Hypervideo
  Hypervideo, or hyperlinked video, is a displayed video stream that contains embedded, user-clickable anchors, allowing navigation between video and other hypermedia elements. Hypervideo is thus analogous to hypertext, which allows a reader to click on a word in one document and retrieve...
  
   a product placement or a contextual link, clickable graphic or text that provides information related to the content of the video and/or the target of the link being placed.

See also

• Hardware overlay
  Hardware overlay
  In computing, hardware overlay, a type of video overlay, provides a method of rendering an image to a display screen with a dedicated memory buffer inside computer video hardware. The technique aims to improve the display of a fast-moving video image — such as a computer game, a DVD, or the signal...
  
  
• Texture mapping
  Texture mapping
  Texture mapping is a method for adding detail, surface texture , or color to a computer-generated graphic or 3D model. Its application to 3D graphics was pioneered by Dr Edwin Catmull in his Ph.D. thesis of 1974.-Texture mapping:...
  
  
• Subtitle (captioning)
  Subtitle (captioning)
  Subtitles are textual versions of the dialog in films and television programs, usually displayed at the bottom of the screen. They can either be a form of written translation of a dialog in a foreign language, or a written rendering of the dialog in the same language, with or without added...
  
  
• X video extension
  X video extension
  The X video extension, often abbreviated as XVideo or Xv, is a video output mechanism for the X Window System. The protocol was designed by David Carver; the specification for version 2 of the protocol was written in July 1991. Its main use today is to rescale video playback in the video controller...