Chapter 1
Introducing the Profile PRO Series
22
Profile PRO Series
Video Compression
The i960 on the master board is used to control data flow and compression
coefficient loading of the JPEG codecs or, if present, MPEG encoders and
decoders. The amount of JPEG video compression varies according to the
setting of the compression coefficient; the amount of MPEG video compression
varies according to the bit rate. Higher compression ratios or bit rates store
more video, but the result is lower quality video. On the other hand, lower
compression ratios or bit rates result in higher quality video and less storage
capacity. Audio, however, is not compressed.
Since the video compression ratio can be varied to change the video quality
given available storage time, the amount of storage depends on your choice of
compression ratio. A quick rule of thumb is that five minutes of JPEG
video—plus four channels of audio and two channels of timecode—is roughly
equal to one gigabyte of disk storage at 50,000 bytes per field in the 525
standard video format. For example, a PDX218 Disk Expansion unit expands
storage up to twelve hours and using multiple PRS255 RAID Storage Systems
can bring it up to approximately 96 hours. For video stored in the MPEG format
at an average 12 Mbps, you can just about double these capacities.
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 frames and
B frames.
An I-frame (also known as an I-picture or Intra-picture) is analogous to a single
motion JPEG frame, where all data required to display a frame is stored in one
picture. A P picture (also called a predictive picture) uses a motion vector to
predict what will happen in the next frame and contains only the changed data,
rather than passing along another complex frame of video. In addition, a
B picture (known also as a bidirectional picture) relies on data from both
backward and forward motion vectors to determine how a future frame will be
composed. In general, the longer the GOP, the more efficient your MPEG video
stream will be.
In addition to video compression, the disk recorder boards also integrate the
digital audio data coming from the EISA bus, with up to four channels of audio
per channel of video. These recorder boards communicate with the SCSI-2
interface using a Direct Memory Access (DMA) interface. The Profile PRO
Summary of Contents for Profile Pro II
Page 18: ...Preface 18 Profile PRO Series...
Page 34: ...Chapter 1 Introducing the Profile PRO Series 34 Profile PRO Series...
Page 96: ...Chapter 2 Using the Profile Configuration Manager 96 Profile PRO Series...
Page 115: ...Emptying the Recycle Bin Profile PRO Series 115 Figure 48 Recycle Bin properties dialog box...
Page 119: ...Viewing Properties Profile PRO Series 119 Figure 51 The transcode history page...
Page 158: ...Chapter 4 Using VdrPanel 158 Profile PRO Series Figure 76 Profile Options dialog box...
Page 183: ...Defining a New Clip Profile PRO Series 183 Figure 87 New Clip dialog box...
Page 202: ...Chapter 5 Using the Profile Disk Utility 202 Profile PRO Series...
Page 266: ...Chapter 8 Using the List Manager 266 Profile PRO Series Figure 131 A basic playback list...
Page 299: ...Configuring Video Resources Profile PRO Series 299 Figure 148 MPEG video track settings...
Page 302: ...Chapter 9 Using the Resource Manager 302 Profile PRO Series Figure 151 JPEG codec check boxes...
Page 311: ...Configuring Timecode Resources Profile PRO Series 311 Figure 158 Timecode Codec check boxes...
Page 316: ...Chapter 9 Using the Resource Manager 316 Profile PRO Series...
Page 342: ...Chapter 10 Using TimeDelay 342 Profile PRO Series...
Page 358: ...Glossary 358 Profile PRO Series...
Page 370: ...Index 370 Profile PRO Series...