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A Two-Stage Multiple Description Video
Coder with Drift-Preventing Motion
Compensated Prediction
Author：Yen-Chi Lee, Yucel Altunbasak, and
Russell M. Mersereau
指導教授：許子衡老師
學生：王志嘉
2016/7/13
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Introduction (i)
Multiple description coding (MDC) is a source
coding technique that exploits path diversity to
increase the robustness of transmitting a compressed
signal over error-prone channels.
In a multiple description coder, several coded streams,
called descriptions ,are generated and transmitted
over different channels
A frame that uses two descriptions.
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Introduction (ii)
Have three possible reconstructions at the decoder. If
the reconstruction is performed by the side decoder, a
prediction mismatch will occur in the following
motion-compensated frame because its prediction will
not be the same as the one used to generate the
prediction error compensation.
This phenomenon is called drift.
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Introduction (iii)
Vaishampayan proposed a “twin-description” interframe video coder that uses two independent
prediction loops.
In order to avoid a prediction mismatch at the decoder
side, they make these two predictions (nearly)
identical by inserting an additional quantizer in each
prediction loop.
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Introduction (iv)
The residual signal is then generated according to this
low-resolution prediction and encoded into two
balanced descriptions using MDSQ (Multiple
Description Scalar Quantizer).
This structure based on two prediction loops can be
further improved by incorporating estimation theoretic
methods, which try to refine the reconstruction level
of the residual signal in such a way that the additional
coarse quantization is effectively removed
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Introduction (v)
Reibman presented another multiple description coder
for video that uses three prediction loops:
1)
2)
A central prediction loop that generates two descriptions of
the residual to provide robust transmission.
Two other prediction loops that produce side information to
prevent drift.
To prevent drift, the two side prediction loops encode
the amount of reconstruction error caused by
prediction mismatch as side information.
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Introduction (vi)
Tang also proposed a multiple description coder using
a matching pursuit algorithm for wireless video based
on this three-prediction-loop structure.
The method is a post-processing approach whose
performance is affected by the statistics of the video
content.
In this paper, we propose a simple but efficient twostage MDC in the central prediction loop based on
Reibman’s three-prediction-loop structure.
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The Three-Prediction-Loop Structure (i)
Reibman proposed adding two more prediction loops
at the encoder side to mimic all three possibilities that
the decoder may encounter.
This forms the three-prediction-loop structure shown
in Figure 1.
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Fig.1
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The Three-Prediction-Loop Structure (ii)
P0 is first obtained by performing a motioncompensated prediction from the reference frame
reconstructed using two descriptions.
r0 is generated by calculating the difference between
the original frame F and the prediction P0, is encoded
by taking a discrete cosine transform (DCT) followed
by a quantization operation.
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The Three-Prediction-Loop Structure (iii)
The encoder then mimics the situation when the
decoder only receives one description of the reference
frame. The side information is given by the formula:
Ff
denote the DCT and the quantization
operations, respectively.
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The Three-Prediction-Loop Structure (iv)
At the decoder side, if P0 is available, the frame is
reconstructed as
If P0 is not available, but either P1 or P2 is available,
we use the received description and the corresponding
side information to perform the reconstruction using
the equation:
is the decoded side information from Si
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The Modified Three-Prediction-Loop:
Two-Stage MDC Structure
We modify the three-prediction-loop structure so that
the side information can be exploited when no errors
occur.
We also propose a two-stage MDC method and further
modify the central prediction loop to effectively use
this additional information to increase the
reconstruction quality.
Fig.2 shows the modified three-prediction loop
structure.
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Fig.2
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Side Prediction Loop Modifications (i)
The side information is seen to depend on the residual
signal r0. It can be expressed as:
We group the last three terms in Equation (4) into a
single term Gi so that the side information can be
written as
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Side Prediction Loop Modifications (ii)
Since the DCT is also linear, Equation (5) could be
expressed as:
The quantized r0 can be easily retrieved by subtracting
the encoded Gi from Si
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Side Prediction Loop Modifications (iii)
The formation of the side information is now altered.
The new side information is given by
Gi is equal to p0-piDdd
The residual signal
The modified side information
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Side Prediction Loop Modifications (iv)
Dd
We can exactly retrieve the quantized residual signal
by subtracting
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Two-Stage MDC in the Central
Prediction Loop (i)
The decoder is now able to obtain another quantized
representation of the residual signal .
The central prediction loop also produces a quantized
residual signal , from and .
We should try to combine both and to increase the
reconstruction quality of the residual signal. But in
this case cannot be used to improve the
reconstruction quality of the residual signal.
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Two-Stage MDC in the Central
Prediction Loop (ii)
We adopt the concept of MDSQ to improve the
reconstruction quality of the residual signal.
We employ an additional MDSQ in the central
prediction loop before r0 is coded into two
descriptions.
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Two-Stage MDC in the Central
Prediction Loop (iii)

The central prediction loop performs multiple
description decoding to obtain from the two
descriptions and .
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Experiments (i)



We adopted the MDSQ technique to the second-stage
MDC encoder in Figure 2.
The four standard test sequences ,FLOWER
GARDEN, FOOTBALL, MOBILE, and TABLE
TENNIS ,were used to evaluate the performance of
the proposed method.
In our simulation, the average burst error length is set
to 5. We compared both methods at packet loss rates
of 0.0001, 0.001, 0.005, 0.01, 0.02, 0.05, 0.1,and 0.2.
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Experiments (ii)

Fig.3 shows the average PSNR (peak signal-to-noise
ratio) performance versus the packet loss rate for the
four video sequences.
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Experiments (iii)

PSNR comparisons of four video sequences, (a)
FLOWER GARDEN, (b) MOBILE, (c) TABLE
TENNIS, and (d) FOOTBALL, between the
conventional and the proposed methods with respect
to difference packet loss rates. The packets are
discarded based on a two-state Markov model (Gilbert
model) with average burst error length of 5.
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Fig.3
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Conclusion


A simple but efficient two-stage multiple description
video coder in prediction mode based on a three
prediction loop structure is proposed.
The proposed method utilizes the side information to
increase the quality when no errors occur but still keep
the capability of reducing the drift.
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