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
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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.)
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We propose using reverse-encoded bitstreams
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
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Random Access
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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
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To solve the problem of the backwardplay 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.
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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
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CR_C : the cost of decoding the next requested Pframe from the current displayed frame.
CR_FI : the cost of decoding the next requested Pframe from the closest I-frame in the forward
bitstream.
CR_RI : the cost of decoding the next requested Pframe from the closest I-frame in the reverseencoded 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
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Random Access
Frame Nj is the random access point
NRI is the position of the I-frame in the reverse bitstream
We 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
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DFR / DRF : a bitstream used for switching from the I- or
P-frames of the forward/reverse bitstream to the Pframes 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
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Reverse-encoded bitstream to simplify the
client machine complexity.
Minimum-cost frame-selection scheme to
minimize 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.