Representation Switch Smoothing for Adaptive HTTP Streaming

REPRESENTATION SWITCH
SMOOTHING
FOR ADAPTIVE HTTP STREAMING
Michael Grafl and Christian Timmerer
4th International Workshop on Perceptual Quality of Systems (PQS 2013),
September 2-4 2013, Vienna, Austria
M. Grafl and C. Timmerer 1Representation Switch Smoothing

OUTLINE
 Introduction & Concept
 Implementation Options
 Evaluation & Results
 Discussion
 Conclusions
M. Grafl and C. Timmerer Representation Switch Smoothing 2

INTRODUCTION
 DASH: Dynamic Adaptive Streaming over HTTP
 Client downloads segments sequentially in best fitting
representation (quality, resolution, frame rate)
 Dynamically switch between representations (e.g.,
based on available bandwidth)
 Representation switches annoying to viewers
 How to reduce the quality impact of
representation switches?

CONCEPT
 Avoid abrupt
quality switches
 Smooth
transition
between
representations
Representations min bitrate
& quality
max bitrate
& quality
Time
Abrupt
change of
playback
quality
Representations
min bitrate
& quality
max bitrate
& quality
Time
Original
quality of
segment
Smooth transition
between
representations

IMPLEMENTATION OPTIONS
 Pre-decoder
 Remove picture fidelity data (transform coefficients) before
the decoder
 Suitable for Scalable Video Coding (SVC)
 Causes motion compensation drift
 In-decoder
 Remove picture fidelity data inside the decoder
 Less drift but decoder-dependent
 Post-decoder
 Post-processing filter mimicking distortion
 No drift
 Coding format independent

IMPLEMENTATION OPTIONS
 In-decoder implementation option
for SVC
Motion
Compen-
sation
Inverse
Quanti-
zation
Inverse
Quanti-
zation
Inverse
Trans-
form
Decoded
Picture Buffer
Predict-
ion
Data
Base
Residual
Enhance-
ment
Layer
Residual
+
+
+
+ Decoded
Frame
Motion
Compen-
sation
Inverse
Quanti-
zation
Inverse
Quanti-
zation
Inverse
Trans-
form
Decoded
Picture Buffer
Predict-
ion
Data
Base
Residual
Enhance-
ment
Layer
Residual
Decoded
Frame
+
+
+
+
Inverse
Trans-
form
+
+
Representation
Switch Smoothing

EVALUATION
 Subjective evaluation of down-switching scenario
 2 test sequences (15 sec, from TearsOfSteel,
1280x720, H.264, no sound)
 Quality Switching (after 10 sec) vs.
 Representation Switch Smoothing (5-sec transition)
 18 participants
 Pair-wise comparison (may repeat versions)
 Rating: Version a, Version b, No difference
 Smoothing simulated through repeating full-sequence
encoding and extraction of relevant frame
 Issue: temporal noise due to moving blocking artifacts

EVALUATION
 Per-frame PSNR for test sequences
high motion low motion

SCREENSHOTS
Sequence 1 Sequence 2

RESULTS
Preferred
Version
Sequence
Quality
Switching
Representation
Switch
Smoothing
No
Difference
Sequence 1 5 7 6
Sequence 2 3 12 3

DISCUSSION
 Representation Switch Smoothing: significant
improvement for Sequence 2 (low-motion)
 Temporal noise may have impacted results
 Longer transitions (e.g., 10 sec) may improve QoE
 Possible influence factors:
 Base quality, bitrate difference, cuts, resolution, spatio-
temporal complexity, duration of low quality
 Alternative approach: limited steps below
just-noticeable difference

CONCLUSIONS
 Idea: reduce annoyance of abrupt quality switches
by a smooth transition
 Avoid viewer distraction in adaptive HTTP streaming
 Implementation options discussed
 Subjective evaluation for down-switching
 Possible influence parameters identified
 Future work:
 Improve implementation (avoid temporal noise)
 Analyze impact of influence parameters
 Evaluated up-switching scenario

THANKS FOR YOUR ATTENTION!
Questions?
http://itec.aau.at/~mgrafl | @MyKey_ – http://aau.at/tewi/inf/itec/mmc/ | @itecMMC

Representation Switch Smoothing for Adaptive HTTP Streaming

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