An inherent problem with any communication system is that information may be altered or lost during transmission, due to channel noise. This presentation aims to assess multiple error resilient techniques in video transmission. ----------- Presentation as a part of seminar coursework.

1. EL-400
SEMINAR PRESENTATION ON
LOGO
ERROR RESILIENT VIDEO COMMUNICATION
Under the guidance of
DR. ATHAR ALI MOINUDDIN
Presented by
BILAL ARIF
10LEB148
A4LE-32

2. Outline
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2
ERROR RESILIENCE TECHNIQUES
3
ERROR RESILIENT ENCODING
4
DECODER ERROR CONCEALMENT
5
2
INTRODUCTION
CODEC INTERACTIVE ERROR CONTROL

3. INTRODUCTION
 One inherent problem with any communication system is that
information may be altered or lost during transmission, due
to channel noise.
 The effect of such information loss can be devastating for the
transport of compressed video because any damage to the
compressed bit stream may lead to objectionable visual
distortion at the decoder.
 Issues such as audio-visual synchronization and multipoint
communications further complicate the problem of error
recovery.
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4. Figure 1 shows steps involved in video communication.
Fig.1 A typical video communication system
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5. Fig 2 shows an example of effect transmission errors to a compressed
video stream.
Coded,
No loss
3%
5%
10%
Fig.2 Example of reconstructed video frames from a H.263 coded
sequence, subject to packet losses .
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6. Why Error Resilience Techniques?
 Unless a dedicated link, that can provide a guaranteed quality of
service is available between the source and destination, data
packets may be lost or corrupted.
 Error-free delivery can be achieved through retransmission of
lost/damaged packets using mechanisms such as Automatic
Repeat Request (ARQ).
 But this introduces delays that are unacceptable for certain realtime applications. The use of retransmission algorithm is also
prevented due to network flooding considerations.
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7. Why Error Resilience Techniques?
 It is important to devise video encoding/decoding schemes
that make the compressed bit stream resilient to transmission
errors.
 Designing proper interfacing mechanisms between codec
(encoder and decoder) and the network, so that the codec can
adjust its operations based on the network conditions, is also
important.
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8. ERROR RESILIENCE TECHNIQUES
 The Error Resilience (ER) techniques can be classified into
three groups:
 (I) Those introduced at the source and channel encoder, to
make the bit-stream more resilient to potential errors;
 (II) Those invoked at the decoder upon detection of errors,
to conceal the effect of errors; and
 (III) Those which require interactions between the source
encoder and decoder, so that the encoder can adapt its
operations based on the loss conditions detected at the
decoder.
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9. ERROR RESILIENT ENCODING
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10. ERROR RESILIENT ENCODING
 The encoder operates in such a way so that transmission errors
on the coded bit stream will not adversely affect the decoder
operation.
 ER encoders are less efficient compared to other coders, as
they use more bits to obtain the same video quality in the
absence of any transmission error.
 The extra bits are called redundancy bits, introduced to
enhance video quality when bit stream is subjected to
transmission errors.
 Achieving maximum gain in error resiliency with smallest
amount of redundancy is the design goal.
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11. ERROR RESILIENT ENCODING
 There are various techniques to introduce redundancy in the
bit stream some of which are :
 Layered coding (LC) with unequal error protection;
 Multiple Description Coding (MDC);
 Error Resilient Prediction
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12. ERROR RESILIENT ENCODING
Layered coding with unequal error protection(UEP)
 Video is coded into a base layer and one or more
enhancement layers,
 Base layer can provide low but acceptable level of quality,
 Enhancement layers incrementally improve the quality,
 Users with different bandwidth capacity can access the
same video at different quality levels, (illustrated in Fig 3),
hence it is also called scalable coding.
 Paired with UEP in transport system giving base layer more
protection by assigning a more reliable sub-channel or
allowing more retransmissions.
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13. ERROR RESILIENT ENCODING
Fig.3 Illustration of scalable coding
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14. ERROR RESILIENT ENCODING
 Multiple Description Coding (MDC)
 Independently-decodable and mutually-refinable streams of a
video source are generated.
 These streams are called descriptions.
 They are transmitted separately, possibly through different
network paths.
 These multiple descriptions together enable the decoder to
successfully decode the video ( depicted in Fig.4)
 Advantage of MDC over LC is that it does not require special
provisions in the network to provide a reliable sub-channel.
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15. ERROR RESILIENT ENCODING
Fig.4 Depiction of MDC (Black boxes indicate lost information)
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16. ERROR RESILIENT ENCODING
 Error Resilient Prediction
 Temporal prediction is a major cause of incurrence of
transmission errors.
 Once an error occurs so that a reconstructed frame at the
decoder differs from that assumed at the encoder, the reference
frames used in the decoder from there onwards will also differ
in a similar fashion and consequently all subsequent
reconstructed frames will be in error.
 Insertion of Intra-Blocks or I-Frames is one of the solutions to
stop temporal error propagation as prediction for an I-frame
depends only on the current frame, there is no error
propagation from the previous frames.
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17. DECODER ERROR CONCEALMENT
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18. DECODER ERROR CONCEALMENT
Fig.5 Illustration of
Decoder Error
Concealment
 Recovery or estimation of lost information due to transmission
errors.
 Packet losses typically lead to the loss of an isolated segment
of a frame.
 The lost region can be “recovered” based on the received
regions by spatial/temporal interpolation.
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19. CODEC INTERACTIVE ERROR CONTROL
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20. CODEC INTERACTIVE ERROR CONTROL
 Feedback is provided from decoder to the encoder.
 Decoder can inform the encoder about the information
corrupted by errors and encoder operation can adjusted to
suppress or eliminate the effect of such errors.
 If the network protocol supports ARQ, retransmission of
lost packets could be done but it introduces delay.
 If online correction of errors cannot be afforded then it is
important to limit the propagation scope of such errors.
 This approach can reduce the losses, at the cost of
increased complexity.
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21. CODEC INTERACTIVE ERROR CONTROL
 Reference Picture Selection (RPS)
 If the encoder learns through a feedback channel about
damaged parts of a previously coded frame, it can decide
to code the next frame not relative to the most recent, but
to an older reference picture, which is known to be
available in the decoder.
 The penalty for using the older reference picture is
significantly lower, if the reference picture is not too far
away.
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22. CONCLUSION
 We came across various techniques which help us to combat with
transmission errors that are incurred in video communication.
 For real-time applications techniques employing retransmissions cannot
be put into use, instead ER techniques are employed.
 ER encoders provide resilience at the cost of decrease in efficiency.
 Even when a damaged bit stream is received, we can improve the
quality of service using a well-designed decoder through the
Concealment Technique.
 Feedback between the codec can help to provide error resilience
 Error Resilient Video Communication is very much possible,
provided these techniques are exploited in a proper way.
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23. REFERENCES


Mohammad Kazemi, Shervin Shirmohammadi, Khosrow Haj Sadeghi, “A Review
of Multiple Description Coding Techniques for Error-Resilient Video Delivery”.
Springer-Verlag Berlin Heidelberg 2013, April 2013.

Ramdas Satyan , Sunday Nyamweno, Fabrice Labeau, “Novel prediction schemes
for error resilient video coding”, Signal Processing: Image Communication,
Elsevier, pp.648-659. May 2010.

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Y. Wang, S. Wengar, J. Wen and A. K. Katsagellos, “Error Resilient Video
Coding Techniques, Real Time Video Communication Over Unreliable
Networks”: IEEE Signal processing Magazine, pp. 61-82. July 2000.
Y. Wang and Q. Zhu, “Error control and concealment for video communication: a
review,” Proceedings of the IEEE, vol. 86, pp. 974-997. May 1998.

24. THANK YOU
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