User manual
4.4.3. Choice of Bitrate
How to Read the Following Tables?
1. Video Bitrate: value set by the user in the advanced parameters window of the XT3
server
2. Fields/Block: numbers of video fields that can be stored in one disk block of 8MB,
taking into account 8 audio tracks.
3. Actual Bandwidth: this is the actual disk/network bandwidth that is required for the
real time record or real time playback of one video stream and its associated audio
tracks.
4. Max. RT Channels: this is the maximum number of video channels (real time record or
real time playback) that one XT3 server can support for a given frame rate and bitrate.
Since an XT3 server can have a maximum of 6 local video channels, any value higher
than 6 means that these additional real time access can be used over the XNet2 SDTI
network.
For mixed configuration with standard and super motion channels on the same server,
the following rule must be used to ensure that the settings do not exceed the
maximum bandwidth of the server : (nbr of standard channels x their actual bandwidth)
+ (nbr of super motion channels x their actual bandwidth) must be lower than or equal
to 250 MB/s.
Example: Can I run an XT3 server with 2 records (1 super motion + 1 standard) + 2
play (1 super motion + 1 standard) in Avid DNxHD® with a video bitrate of 100Mbps
in “PAL” ?
Calculation: 1 standard rec/play at 100Mbps uses 13.3 MB/s ; 1 super motion
record/play at 100Mbps uses 40.0 MB/s; 2 x 13.3 + 2 x 40.0 = 126.6 MB/s.
Conclusion: this configuration is supported.
5. Network transfers: the maximum bandwidth over the XNet2 SDTI network is
approximately 110 MB/s. To determine the number of real time transfers that can
occur simultaneously over the network, this number must be divided by the actual
bandwidth given in the table for a selected bitrate.
Example: How many real time transfers can I do over an XNet2 SDTI network (set at
1485Mbps) if I work with Apple ProRes 422 at 145Mbps in “NTSC” ?
Calculation:
Maximum SDTI bandwidth / Actual Bandwidth = real time transfers:
110MB/s / 18.4MB/s = 6 real time transfers.
Note: This number is the maximum that the network connection can support. Of
course it is also necessary that the XT3 where the material is stored has enough local
disk bandwidth to feed the network accesses, on top of its own local channels (see
Max. RT Channels)
To get information on the recording capacity of the servers according to the video bitrates,
refer to section "Recording Capacities" on page 28
XT3 Server- Version 11.01- Hardware Technical Reference Manual
4. Software Specifications 23