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Presentation of the paper at the 4th International Workshop on Perceptual Quality of Systems (PQS 2013), Vienna, Austria, September 2013.
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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?
M. Grafl and C. Timmerer Representation Switch Smoothing 3
CONCEPT
Avoid abrupt
quality switches
Smooth
transition
between
representations
M. Grafl and C. Timmerer Representation Switch Smoothing 4
Rep
rese
nta
tio
ns
min bitrate & quality
max bitrate & quality
Time
Abrupt change of playback quality
Rep
rese
nta
tio
ns
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
M. Grafl and C. Timmerer Representation Switch Smoothing 5
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
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
EVALUATION
Per-frame PSNR for test sequences
M. Grafl and C. Timmerer Representation Switch Smoothing 8
high motion low motion
SCREENSHOTS
M. Grafl and C. Timmerer Representation Switch Smoothing 9
Sequence 1 Sequence 2
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
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
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
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
