Page 286 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

10.6 Video over Internet protocol 275
Frame display order
Frame1 3 4 2 6 7 5
1234567
FIGURE 10.31
transit order
Intra (I) frame
Bidirectional prediction
Bidirectional (B) frame
Predicted (P) frame
Sequential ordering of the I, P, and B frames.
“I-frames” (for “intra frame”), “B-frames” (for “bidirectional frame”), and “P-frames” (for “pre- dicted frame”). The sequencing of these frames is quite ingenious as displayed in Figure 10.31.
The highest quality picture is obtained in video compression schemes with slight movement of one object within the frame while the remainder of the frame stays consistent. An example of a high-quality compressed video would be a news announcer who moves with only head gestures with a steady and static background. You will notice from a rapidly moving compressed video sig- nal (for instance, an inexperienced camera operator moving the camera in an unsteady fashion) that substantial smearing of the image occurs. The reason for this phenomena is the P, B, and I frames are not able to generate steady duplication and prediction as the repeating portions of the frame decrease. This will have a substantial implication for lower bandwidth links such as those present while performing high-definition video over long lengths of copper (such as a submersible’s tether) or with transmission of video over Internet protocol.
10.6 Video over Internet protocol
The modern customer of subsea services is quite impatient to receive the product of the subsea inspection or intervention tasks—oftentimes requiring immediate video. Thus, the people in the field (who often do not understand the physics behind the subsea object or structure being observed) are tasked with feeding the video quickly back to the customer’s office (to the people who designed or are responsible for that structure). With the advent of high-bandwidth wireless and