An Error-Resilient GOP Structure for Robust Video Transmission

Tao Fang, Lap-Pui ChauElectrical and Electronic Engineering, Nanyan Techonological University

IEEE Transactions on Multimedia, Dec. 2005

Outline

Introduction Proposed GOP Structure Efficient Reverse-play Functionality of

the Proposed GOP Structure Experimental Results Conclusion

Introduction(1/4) GOP

I, P, B picture I frame at the beginning of a GOP

A basic entry point to facilitate random seeking or channel switching

Provide coding robustness to transmission error

Introduction(2/4) Predictive coding techniques

Effect of channel errors on the video can be extremely severe

A novel GOP structure for robust video transmission Insert the I frame in the middle of the GOP

Introduction(3/4)

Advantage of the proposed GOP structure Improve the robustness of the streaming

video without reducing any coding efficiency

Provide reverse-play operation with much less requirement on the network bandwidth

Introduction(4/4) MEPG is designed for forward-play

operation Predictive processing complicate the reverse-

play operation Straightforward but naïve approach

Decode the GOP up to the current frame, and then go back to decode from the beginning of the GOP again up to the next frame to be displayed

Require high bandwidth of the network Some works on the implementation of reverse-

play Require much computation or extra decoder

complexity

Proposed GOP Architecture Not including B frames in the following analysis for

legibility but without loss of generality I frame will be stored in the reference buffer

jini PPPPIP 11

Optimal Position of I frame in a GOP(1/3)

Built model to describe the effect of error on the decoded video quality PSNR, MSE

Involve complicated parameter estimation Length of error propagation (LEP) Number of impaired macroblocks (MBs)

Totally n+1 frames in a GOP with one I frame and n P frames

Optimal Position of I frame in a GOP(2/3) A lost slice belongs to ：

I frame LEP = n+1

Forward predicted P frames (Pk , k≦i) LEP = i-k+1

Backward predicted P frames (Pk’ , k≦n-i) LEP = n-i-k+1

Average LEP

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Optimal Position of I frame in a GOP(3/3) By solving , we can get the optimal

position of I frame in a GOP, i.e.,average

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Analysis of Coding Efficiency, System Delay and Complexity(1/3)

Coding efficiency Temporary dependency depends on the

predicting distance and inherent characteristics of the video sequences Thus, coding efficiency of Proposed GOP is

compatible with that of MPEG GOP Proposed GOP with higher quality while

consuming fewer bits LEP is halved by inserting the I frame in the

very middle of a GOP

Number of bits used by conventional MPEG and this work of Mother & Daughter QCIF, Foreman QCIF, and Stefan QCIF

Corresponding PSNR value of Mother & Daughter QCIF, Foreman QCIF, and Stefan QCIF

Analysis of Coding Efficiency, System Delay and Complexity(2/3) System delay

Sequence , coding and transmitting order is

For displaying , maximal delay will be n-i frames Tradeoff between delay and robustness

Optimization problem becomes

iinin PPIPPPP ...... 21'1

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iin PPPPPIP ...... 21''

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Analysis of Coding Efficiency, System Delay and Complexity(3/3) System complexity

For conventional coder, the buffer stores one previous frame for reference

For proposed GOP, we enlarge the buffers Store an extra I frame at encoder Maximal number of frames stored is n-i for orderly di

splay (display ) 'inP

Efficient Reverse-Play Functionality of the Proposed GOP Structure

The proposed approach outperforms the conventional method, where it saves a lot of retransmissions

And the proposed GOP can reduce the required bandwidth significantly

Bandwidth requirement with respect to the reverse play operation for sending (a) Mother & Daughter, (b) Foreman, and (c) Stefan

Experimental Results In the experiment, specify the frames

where slice loss happens beforehand Slice losses at frame 7, 19, 33, 46, 59, 72 These frames are the 6th, 7th, 10th, 1st, 3rd, 5th P

frames after each I frame For instance, for slice loss in frame 46, 1st frame

after I frame The error propagate to all the following P

frames by conventional MEPG GOP The error propagate stops at 6th frame, say

frame 51

Experimental Result

Average PSNR comparison according to different delay requirements. (a) Mother & Daughter. (b) Foreman. (c) Stefan

Experimental Results Compared with a compliant structure that

starts with an I-frame with compliant prediction directions Put more B frames in the beginning of the GOP

to improve the robustness Distances between P (or I) frames are not equal Low compression efficiency due to long

predicting distance between P (or I) frames Not good to make the distances between the P

(or I) frames different too much

Experimental Results

The number below each frame represents the LEP if a lost slice belongs to this frame LEP of proposed structure is 34p LEP of compliant structure is 42p

Experimental Results

Conclusion A novel GOP structure that inserts an I

frame in a GOP to improve the robustness of the video transmission

From simulation results, the proposed GOP outperforms the conventional GOP

But, it inevitably increase the delay and complexity of the system

And the efficient reverse-play operation for the video streaming system of the proposed structure