Grass Valley PROFILE FAMILY v.2.5 - Manual (Page 21)

Profile Family 21
Chapter
1
Introducing the Profile Family
The Profile PDR100 Video Disk Recorder and the Profile PDR 200 and
PDR 300 Video File Servers store broadcast-quality motion JPEG or MPEG
(PDR200 and PDR300 only) video and CD-quality audio on computer disk
drives rather than on video tape, allowing almost instant access to any timecode
location of your video and audio material.
A Profile system is more than just a one-for-one replacement of a VTR: it can
have up to six record and eight playback video channels. Clips are available on
all channels at once, so you can play a clip on more than one channel at the same
time, without making a copy of it. Since each channel is independent of the
others, each playback can start at a different time and at a different place in the
clip.
You can even start playing a clip while it’s still being recorded. Just start
capturing the clip on one channel, wait about five seconds, and then play the clip
back on another channel. This kind of control makes the Profile system an ideal
solution if you want to go to air with a clip before you are finished recording it.
NOTE: Profile System Software version 2.5 supports the PDR 200, the
PDR300, and, when upgraded with a Master and Slave Enhanced
Disk Recorder (EDR) boards, the PDR100. In addition, version 2.5
runs on Microsoft Windows® NT™ 3.51 and 4.0.
This version of system software offers support for the MPEG-2 4:2:2 @ Main
Level encoder/decoder boards, which are standard in the PDR300. Upgrading
your PDR200 with MPEG can approximately double its video/audio storage
capacity and enables much faster data transfers over Fibre Channel. The MPEG
encoder offers both 4:2:2 and 4:2:0 chroma sampling, variable bit rates from 4
Mb/s to 50 Mb/s, and group of picture (GOP) structures from I-frame only to
16-frame GOPs.
MPEG uses motion prediction to increase efficiency—essentially, it uses lower
data rates because it does not duplicate video that does not change from frame
to frame. MPEG accomplishes this through both backward and forward
prediction. To do this, it uses GOPs, consisting of I-frames, P pictures and B
pictures.