GDCL Home About GDCL DirectShow WinNt & WDM

Video Capture on NT 4.0

If you need support for Video Capture on Windows NT 4.0, then your choices of interface are limited. You will need to write a 32-bit VfW device driver. For application interfaces you can use either AVICap or DirectShow.

NT Video Capture Drivers

The Video capture API on Windows NT 4.0 is a user-mode interface. You will need to supply a user-mode DLL that supports the VfW installable driver interface: OpenDriver and SendDriverMessage. Capture formats and properties can only be set by dialogs: your user-mode dll will supply these ioctls.

You will also need a kernel-mode device driver that you communicate with via IOCTLs. The separation between the user-mode and kernel mode pieces is up to you: however, the NT DDK includes a pair of C libraries (VCUser and VCKernel) that manage the communication and simplify the device driver writer's job, in a similar manner to a port/miniport split. Since these libraries are provided in source form they can be customised to your needs.

Performance

Video capture performance on NT 4 using AVICap and 32-bit VfW drivers can be very impressive. AVICap uses an efficient overlapped, unbuffered writing scheme to write to the disk, and in combination with NT's striping on a fast array of disks can easily meet professional broadcast quality requirements. Performance using DirectShow is unlikely to be better: however, using DirectShow gives much more flexibility for non-file writing needs such as video conferencing. Even Microsoft acknowledges that VfW capture drivers will be around for a while still for file-writing tasks.

Video Capture Topics

Video Capture Overview
Video Capture on NT 4.0
DirectShow and Video Capture