EVS XT2 - Raid Level: 3; Interpolation

XT Series DISK RECORDER - Version 9.00 - Hardware Technical Reference Manual
EVS Broadcast Equipment SA – April 2008
Issue 5.00
17
• When using the Avid DNxHD® codec, we advise to work at 100Mbps if
the picture quality is satisfactory Æ the XT[2] can sustain 6 local
channels + 5 network transfers.
1.5.8 RAID LEVEL: 3
The Video Raid uses striping process across 5 disk drives. The video and
audio data is striped over the first 4 drives while the parity information is
saved on the fifth drive. If one drive is damaged, the Video Raid can use
the parity information to recover the missing information, so that
operation can continue seamlessly without bandwidth loss.
For more information on online rebuild, refer to the section dedicated to
this subject in the XT Technical Reference manual.
1.5.9 INTERPOLATION
The playing back of smooth slow motion pictures carries specific issues:
since some fields must be repeated at regular interval to provide the
video at the playback speed required by the operator, parity violation
appears regularly on the output video signal. This issue is specific to
interlaced formats (525i, 625i and 1080i) and does not concern
progressive formats (720p).
If O and E represent respectively the odd and even fields of a standard
video signal (50/60 Hz), we have:
The original video signal:
O E O E O E O E O E O E O E O E
The output video signal at 50% speed:
O O E E O O E E O O E E O O E E
The output video signal at 33% speed:
O O O E E E O O O E E E O O O E
The output video signal at 25% speed :
O O O O E E E E O O O O E E E E
Fields with parity violation are shown in bold, underlined letters. As it
appears from the above table, whatever the playback speed (with the
exception of the normal 100% playback speed), a number of fields violate
the normal parity of the output signal. This parity violation induces a 1-
line shift of the field, resulting in a vertical jitter of the picture. The jitter
frequency depends upon the chosen playback speed.