uring the video blanking interval. There are two of them, the "raw" and "sliced" interfaces, which differ in the amount of processing of the VBI data performed in hardware.
The radio interface provides access to audio streams from AM and FM tuner devices.
Other types of devices are possible. The V4L2 API has some stubs for"codec" and "effect" devices, both of which perform transformations onvideo data streams. Those areas have not yet been completely specified,however, much less implemented. There are also the "teletext" and "radiodata system" interfaces currently implemented in the older V4L1 API; thosehave not been moved to V4L2 and there do not appear to be any immediateplans to do so.
Video devices differ from many others in the vast number of ways in whichthey can be configured. As a result, much of a V4L2 driver implements codewhich enables applications to discover a given device's capabilities and toconfigure that device to operate in the desired manner. The V4L2 APIdefines several dozen callbacks for the configuration of parameters liketuner frequencies, windowing and cropping, frame rates, video compression,image parameters (brightness, contrast, ...), video standards, videoformats, etc. Much of this series will be devoted to looking at how thisconfiguration process happens.
Then, there is the small task of actually performing I/O at video rates inan efficient manner. The V4L2 API defines three different ways of movingvideo data between user space and the peripheral, some of which can be onthe complex side. Separate articles will look at video I/O and thevideo-buf layer which has been provided to handle common tasks.
Subsequent articles will appear every few weeks, and will be added to thelist below: