MPEG Video Streaming with VCR Functionality

Chia-Wen Lin, Jian Zhou, Jeongnam Youn, Ming-Ting Sun

IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS FOR VIDEO TECHNOLOGY, MARCH 2001

Introduction A key technique that enables fast and user

friendly browsing of multimedia content is to provide VCR functionality.

VCR functionality includes forward, backward, random access, fast-forward/backward.

MPEG video compression is based on motion compensated predictive coding with an I-B-P frame structure.

We investigate the impacts of the VCR functionality on the network traffic and the video decoder complexity.

Introduction(cont.) We propose using reverse-encoded bitstrea

ms at the server to resolve the problem of reverse play.

We propose a frame-selection scheme at the server to minimize the required network bandwidth and the decoder complexity.

We describe our implementation of an MPEG-4 video streaming system supporting the VCR functionality.

Impacts of VCR Functionality on Decoder Complexity and Network Traffics

Random Access

Fast-Forward Play

speed-up factor K = 6

Fast-Forward Play We assume the start point of a fast-forward operation is

an I-frame, L= gcd( k, N ) After k/L GOPs, the frame to be displayed will again be an I-frame.

If N is relatively large compared to k, will grow almost linearly as k increases, thereby leading to a linear increase of the decoding complexity and the network traffics

Average number frames and bit-rates for sending the “Moblie and Calendar” sequence over network with respect to different speed-up factors in fast-forward play

Supporting Full VCR Functionality with Minimal Network Bandwidth and Decoder Effort

To solve the problem of the backward-play operation, we propose to add a reverse-encoded bitstream in the server.

After we finish the encoding and reach the last frame of the video sequence, we encode the video frames in the reverse order to generate a reverse-encoded bitstream.

We arrange the encoding so that the I-frame in the reverse bitstream are interleaved between I-frames in the forward stream.

Two metadata files recording the location of the frames in each compressed bitstream are also generated so that the server can switch from the forward-encoded bitstream to the reverse-encoded bitstream.

Dual Bitstreams with Least-Cost Frame Selection

CR_C : the cost of decoding the next requested P-frame from the current displayed frame.

CR_FI : the cost of decoding the next requested P-frame from the closest I-frame in the forward bitstream.

CR_RI : the cost of decoding the next requested P-frame from the closest I-frame in the reverse-encoded bitstream.

The reference frame to the next requested frame with the least cost will be chosen to initiate the decoding.

Example : Fast-backward

Speed-up factor=6,the current position is frame 20, which was decoded using the reverse bitstream(R)display sequence : 20,14,8,2

only need to send and decode 6 frames

Without least-cost scheme, we need to send and decode 13 frames from the reverse bitstream.

Example : Random access

The client requests random access to frame 22 when the current decoded frame if frame 3

Only need to send and decode 2 frames

Without least-cost scheme, we require 9 frame from frame 14 using the forward bitstream.

Performance Analysis of the Proposed Dual-Bitstream Least-Cost Method

Random AccessFrame Nj is the random access pointNRI is the position of the I-frame in the reverse bitstrea

mWe assume N is even and NRI is odd

Fast-forward Play

When N and k are coprime(L=1)

In fact for the cases that N and k are not coprime, the result of (7) and (8) are still very close.

Average number of frames to be sent for decoding a frame and average bit-rates to send “Moblie and Calendar” sequence using the proposed method with respect to different speed-up factors

Drift Compensation

DFR / DRF : a bitstream used for switching from the I- or

P-frames of the forward/reverse bitstream to the P-frames of the reverse/forward bitstream

Pred(A, B) represents an inter-frame prediction process that frame B is predicted from the reference frame A.

DFRn = Pred( Fn , Rn –1 )

DRFn = Pred( Rn , Fn +1 )

Implementation of an MPEG-4 Video Streaming System with Full VCR Functionality

Conclusion Reverse-encoded bitstream to simplify the cl

ient machine complexity. Minimum-cost frame-selection scheme to mi

nimize the number of frames needed to be sent over the network and to be decoded.

Drift-compensation scheme to limit the drift. An MPEG-4 video streaming system with full

VCR functionality can be implemented to minimize the required network bandwidth and decoder complexity.