Table 6.1 IP Overhead
Item Overhead factor Comments
MPEG-2 TS 1.0
UDP 1324/1316 = 1.006 UDP header=8 bytes
IP 1344/1324 = 1.015 IP header=20 bytes
Ethernet 1358/1344 = 1.010 Eth header=14 bytes
Total overhead factor becomes: 1.006 x 1.015 x 1.010 = 1.031 or 3.1% overhead.
Note: The number of MPEG-2 TS packets one can map down into each UDP
frame is variable (between 1 and 7). Usually 7 is used for minimum
overhead. This is also used in the above calculation.
6.2 VCM Video Encoding Functionality
6.2.1.1 Overview
The VCMs process the video input signal into a compressed encoded bit stream in
accordance with the appropriate specification (ITU-T H.264 or ISO/IEC MPEG-4
AVC, MPEG-2 specification (ISO/IEC 13818) or JPEG 2000 specification (ITU-T
Rec. T.802 or ISO/IEC 15444-3)).
6.2.1.2 Functional Description for VCMs
Figure 6.4 VCM Functional Diagram
The 3G/HD/SD-SDI Video Input can be configured to accept either 25 Hz or
29.97 Hz video. The Pre-processor has a video frame re-synchronizer which allows
the video frame rate to be locked to the Unit 27 MHz clock, or to a 27 MHz clock
locked to an external sync input if an External Sync Input option card
(AVP/HWO/EXTSYNC) is fitted. If the unit is configured to be locked to video, then
the frame re-synchronizer is inactive.
The Pre-processor can perform horizontal and vertical scaling and bandwidth
filtering on the video prior to passing it on to the Video Encoder. It can also generate
a test pattern or repeat the last frame received if the video input is not valid.
The Video Encoder processes the video from the Pre-processor into a compressed
encoded bit-stream in accordance with the relevant specification.
It can produce a constant bit rate (CBR) output, which can be set in the range
1 Mbps to 200 Mbps depending upon encoder and profile.
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