VBrick Systems VB6000 Series, Руководство по началу работы

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20 © 2008 VBrick Systems, Inc.
modes regardless of settings. Delay is approximately 350 milliseconds in medium delay mode
and 450 milliseconds in high delay mode. Delay is set in the Configuration: Encoder >
Transport. The default setting for
Delay Mode
is set to
High
.
MPEG-2 Audio
High quality Stereo or Mono audio, fully synchronized with video, may instantly be
transported across the network. VBrick supports 44.1 and 48 kHz sample rates, and data
rates between 192 and 384 Kbps. If the model number ends in -xxx0, the sampling rate can
be 44.1 kHz or 48 kHz. If the model number ends in -xxx1/-xxx2 the sampling frequency is
set at 48 kHz. If the model ends in -xxx0, the transmission rate can be 192, 256 and 384
Kbps. If the model ends in -xxx1/-xxx2 the audio bit rate can be 256 or 384 Kbps. Audio
input and output is standard line-level, as would be found on a conventional VCR. VBrick
offers AudioMate microphone for high quality conference room audio with integral echo
cancellation. For video conferencing applications, appropriate audio conference equipment
such as amplifiers, microphones, and echo control equipment is required.
Table 3. MPEG-2 Optical Loss Budget
MPEG-4
Moving Picture Experts Group MPEG is a standard method of transmitting digital video and
sound in a compressed format that uses less bandwidth than the traditional analog method.
MPEG-4 Part 2 is widely used for distribution of video in the enterprise, on the Internet, and
in mobile applications. VBrick supports a subset of the MPEG-4 Part 2 standard called
Simple Profile. Simple Profile offers optimal interoperability with MPEG-4 from multiple
vendors. MPEG-4 provides moderate resolution and offers scalability for digital video up to
approximately 2 Mbps.
MPEG-4 Encoder Compression
MPEG-4 Part 2 Simple Profile video compression uses many of the same basic compression
features as MPEG-2 discussed above. There are several significant differences worth
mentioning. This protocol does not support B frames. Although B frames offer some
compression benefits, more modern compression schemes such as MPEG-4 gain only
marginal benefits from B frames. In addition B frames always add additional latency since
reordering is required on transmission. This protocol does not have a fixed GOP structure. I
frames are inserted either at a configured rate or when the protocol itself determines that the
scene has changed sufficiently such that it is more efficient to insert an I frame.
MPEG-4 Audio
VBrick's MPEG-4 appliances offer AAC-LC compressed audio. This compression algorithm
is the industry-standard method for audio to accompany MPEG-4 video streams. VBrick
supports Stereo, Mono, and Dual audio for MPEG-4. Sample rates between 8 kHz and 48
MPEG-2 Receiver Sensitivity Transmit Power
MM (maximum reach 3 km) -32 dBm -19 to -14 dBm
SM (intermediate reach 15 km) -28 dBm -15 to - 8 dBm
SM (long reach 1310nM 40 km) -34 dBm -5 dBm
SM (long reach 1550nM 80 km) -34 dBm -5 dBm