This document discusses representation switch smoothing techniques for adaptive HTTP streaming. It presents an implementation that smooths quality transitions when switching between representations by gradually removing picture fidelity data over a transition period. An evaluation compares abrupt representation switching to smoothed switching, finding the latter significantly improved quality of experience for sequences with low motion. Future work could improve the implementation to avoid temporal noise and further analyze the impact of various influence parameters on user quality of experience.

1. 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

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

3. 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?
M. Grafl and C. Timmerer Representation Switch Smoothing 3

4. CONCEPT
 Avoid abrupt
quality switches
 Smooth
transition
between
representations
M. Grafl and C. Timmerer Representation Switch Smoothing 4
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

5. 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
M. Grafl and C. Timmerer Representation Switch Smoothing 5

6. IMPLEMENTATION OPTIONS
 In-decoder implementation option
for SVC
M. Grafl and C. Timmerer Representation Switch Smoothing 6
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

7. 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
M. Grafl and C. Timmerer Representation Switch Smoothing 7

8. EVALUATION
 Per-frame PSNR for test sequences
M. Grafl and C. Timmerer Representation Switch Smoothing 8
high motion low motion

9. SCREENSHOTS
M. Grafl and C. Timmerer Representation Switch Smoothing 9
Sequence 1 Sequence 2

10. RESULTS
M. Grafl and C. Timmerer Representation Switch Smoothing 10
Preferred
Version
Sequence
Quality
Switching
Representation
Switch
Smoothing
No
Difference
Sequence 1 5 7 6
Sequence 2 3 12 3

11. 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
M. Grafl and C. Timmerer Representation Switch Smoothing 11

12. 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
M. Grafl and C. Timmerer Representation Switch Smoothing 12

13. THANKS FOR YOUR ATTENTION!
Questions?
M. Grafl and C. Timmerer Representation Switch Smoothing 13
http://itec.aau.at/~mgrafl | @MyKey_ – http://aau.at/tewi/inf/itec/mmc/ | @itecMMC