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.
Representation Switch Smoothing for Adaptive HTTP Streaming
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
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