NCast Telepresenter M4 - Manual (Page 13)

NCast Telepresenter Reference Manual
2.2. D
IGITIZER
C
APTURE
F
UNCTION
The digitizer capture card selects one of the available four inputs (VGA, DVI, Composite, S-Video) and locks
onto the signal. The signal is converted into the appropriate digital formats, and each pixel in the image is
stored in a local memory buffer on the card. At an appropriate time the pixels in memory are transferred over
the PCI bus to the memory of the main CPU where they are pre-processed and compressed.
If PIP mode is enabled, two signals may be selected (exception: Composite and S-video share one video
decoding chip).
2.3. C
OMPRESSION
The digitized RGB signals are converted in format from an {R,G,B} representation to {Y,U,V}. Industry-
standard compression algorithms are then used to reduce the source data to a more manageable size, and
to generate sequences of I-P-B frames found in MPEG media streams.
2.4. T
RANSMISSION
The MPEG media stream is split into segments, which are then encapsulated into RTP packets according to
the protocol standards set forth in IETF RFC 3016 or RFC 3984 (H.264). These packets are presented to the
Ethernet hardware interface for subsequent transmission on the attached IP network.
2.5. D
ECOMPRESSION
The received packet stream is decompressed and the resulting image is placed into a video frame buffer. At
that instant it will become visible to the receiving viewers.
2.6. D
ISPLAY
F
UNCTION
The display will output imagery from two different sources. If the unit is configured as the sending unit, a
local copy of the captured image (prior to compression, but after capture and conversion to digital format) will
be displayed. If the unit is a receiving unit, the displayed image will be from the remote sender.
2.7. A
UDIO
S
UBSYSTEM
Each Telepresenter supports an audio subsystem consisting of an AC ’97 codec and associated input/output
connectors. The unit has microphone and line-level input signals, and a line-level output signal. Each line-
level connector supports stereo signals.
NCast Corporation Revision 2.2
Page 13