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5G Edge-Based Video Surveillance in Smart Cities
Published in Zoran S. Bojkovic, Dragorad A. Milovanovic, Tulsi Pawan Fowdur, 5G Multimedia Communication, 2020
The other key compression technique is motion compensation applied to macroblocks for P-frames and B-frames. Motion compensation technique use the strong correlation between successive frames in order to maximally reduce the amount of information required to transmit or store them. It consists of predicting most of the pictures of a sequence from preceding and even subsequent pictures. It is done with a minimum of additional information representing only the differences between pictures, and that so-called prediction error is also encoded using DCT and quantization. A P-frame is encoded as a 16 × 16 area relative to the closest preceding I-frame or P-frame, based on movement in the frame. If there is an object displacement in the frame, a motion vector is transmitted. If there are multiple areas of motion, then more motion vectors are added in relation to those positions. The compression rate of P-frames is higher than that of I-frames. B-frames are coded by bidirectional interpolation between the I or P frame which precedes and follows them. The future reference frame is the closest I-frame or P-frame. The difference between a B- and a P-frame is the use of reference areas in a future frame, where the two 16 × 16 macroblock areas are then averaged. B-frames offer the highest compression rate compared with I-frames and P-frames. The arrangement of different types of frames is shown in Figure 16.3a.
Video Compression
Published in Keshab K. Parhi, Takao Nishitani, Digital Signal Processing for Multimedia Systems, 2018
Use of P and B frames increases the level of compression dramatically; however, they also create some inconvenience for display and random access of video sequence. Since the B frames are encoded with reference to both past and future frames, the video frames are encoded and transmitted in an order different from the original, and need to be re-ordered for display, as illustrated in Fig. 2.14. Moreover, decoding of P frames requires decoding of at least two frames including the reference I frame and itself, and decoding of B frames requires decoding of at least three frames including two reference frames and itself. Applications which require access to any part of the video sequence at random result in much more computation complexity, hence an increase in latency. In order to decode the coded bit stream at any arbitrary point, it is necessary to use a certain number of intraframe coded I frames in the video sequence.
6 Video Compression
Published in Wes Simpson, Howard Greenfield, IPTV and Internet Video:, 2012
Wes Simpson, Howard Greenfield
A frame is a single image from a video sequence. In NTSC, one frame occurs every 33 milliseconds; in PAL, one frame occurs every 40 milliseconds.An I frame is a frame that is compressed solely based on the information contained in the frame; no reference is made to any of the other video frames before or after it.A P frame is a frame that has been compressed using data contained in the frame itself and data from the closest preceding I or P frame.A B frame is a frame that has been compressed using data from the closest preceding I or P frame and the closest following I or P frame.A GOP is a series of frames consisting of a single I frame and zero or more P and B frames. A GOP always begins with an I frame and ends with the last frame before the next I frame. The GOP is usually a fixed, repetitive pattern that is configured on the compression device. Different content suppliers may use different GOPs for different channels, but they are normally fixed within each channel.
An Efficient Cloud Storage Model for GOP-Level Video Deduplication using Adaptive GOP Structure
Published in Cybernetics and Systems, 2023
G. Sujatha, A. Devipriya, D. Brindha, G. Premalatha
The “I’ frame is considered the complete frame, which means it contains all the required data during decoding. It does not require anything from the other frame during its decoding. The other frames like “B” and “P” frames may require the support of either the previous frame or the next frame for its reproduction. Logically the “I” frame may be considered a fresh frame or completely a different frame from its predecessors. By considering this logic, the consecutive “I” frames can be identified by calculating the difference between the current “I” frame and the forthcoming frames. When the difference is within the threshold it can be considered as a frame(either “B” or” P”) of the same GOP. The reason is when the two frames are similar to an extent then it is efficient for encoding by registering only the minimal difference which exists between the frames. This is the actual concept of having “B” and “P’ frames. Since the “P” frame contains only the difference between the current frame and the previous one and the “B” frame contains only the difference between the current frame with the previous and next frame. When the difference is greater than the threshold then the corresponding frame can be considered as the next “I” frame to start with the next GOP.