Video capture

Video capture cards are a
class of video capture
devices designed to plug
directly into expansion slots
in personal computers and
servers. Models from many
manufacturers are available;
all comply with one of the
popular host bus standards
including PCI, newer PCI
Express (PCIe) or AGP bus
interfaces.
These cards typically include
one or more software drivers
to expose the cards' features,
via various operating
systems, to software
applications that further
process the video for specific
purposes. As a class, the cards
are used to capture baseband
analog composite video, S-
Video, and, in models
equipped with tuners, RF
modulated video. Some
specialized cards support
digital video via digital video
delivery standards including
Serial Digital Interface (SDI)
and, more recently, the
emerging HDMI standard.
These models often support
both standard definition (SD)
and high definition (HD)
variants.
While most PCI and PCI-
Express capture devices are
dedicated to that purpose,
AGP capture devices are
usually included with the
graphics adapted on the
board as an all-in-one
package. Unlike video
editing cards, these cards
tend to not have dedicated
hardware for processing
video beyond the analog-to-
digital conversion. Most, but
not all, video capture cards
also support one or more
channels of audio.
There are many applications
for video capture cards
including converting a live
analog source into some type
of analog or digital media,
(such as a VHS tape to a DVD),
archiving, video editing,
scheduled recording (such as
a DVR), television tuning, or
video surveillance. The cards
may have significantly
different designs to
optimally support each of
these functions.
One of the most popular
applications for video
capture cards is to capture
video and audio for live
Internet video streaming.
The live stream can also be
simultaneously archived and
formatted for video on
demand. The capture cards
used for this purpose are
typically purchased,
installed, and configured in
host PC systems by hobbyists
or systems integrators. Some
care is required to select
suitable host systems for
video encoding, particularly
HD applications which are
more affected by CPU
performance, number of CPU
cores, and certain
motherboard characteristics
that heavily influence
capture performance.