| Microsoft DirectX 8.1 (C++) |
Microsoft released Video for Windows 1.x in November 1992 for Windows 3.1 and optimized it for capturing movies to disk. Since then, video capture rates have risen dramatically due to use of the PCI bus, bus mastering controllers, NT striped sets, Fast/Wide SCSI, and direct transfer of captured video from adapter memory to disk without data copies. Despite capture rates that now exceed 20 MB per second, and a large number of clients for Video for Windows, deficiencies in the Video for Windows architecture exposed by the emergence of video conferencing required development of a new video capture technology.
The Video for Windows architecture lacks features important to video conferencing, television viewing, capture of video fields, and additional data streams such as vertical blanking interval (VBI). Vendors have extended Video for Windows by implementing proprietary extensions, which are product specific, to circumvent these limitations. However, without standardized interfaces, applications that use these features must include hardware-dependent code. The tight coupling between Video for Windows capture drivers and display drivers means that changes made to capture drivers require changes to display drivers as well.
In addition, the Video for Windows interface, AVICap, doesn't work well with DirectShow because AVICap allocates buffers. If DirectShow is accessed through AVICap, the buffers must be copied at the transition point, which is very inefficient. With the integration of DVD, MPEG decoders, video decoders and tuners, video port extensions (VPE), and audio codecs on single adapters, a unified driver model that supports all of these devices and handles resource contention is needed.