perceived quality for transported video
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Perceived Quality for Transported Video. Nele Van den Ende Reinder Haakma Maddy Janse Peter van der Stok. Overview. Background Adaptation Methods I-Frame Delay Signal-to-Noise Ratio Scalability Research Categories Perception Experiments Method Design Results Summary - PowerPoint PPT PresentationTRANSCRIPT
Perceived Quality for Transported Video
Nele Van den EndeReinder HaakmaMaddy JansePeter van der Stok
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Overview
• Background• Adaptation Methods
– I-Frame Delay– Signal-to-Noise Ratio Scalability
• Research Categories• Perception Experiments
– Method– Design– Results
• Summary• Future Research Questions
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Background
Access to content, anywhere, anytime
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Background
But there are disturbance problems…
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MPEG Encoding
• Compress video• Play back platforms• Types of frames
– Intra-coded, predictive-coded & bi-directionally predictive coded
• Groups of Pictures
I B B P B B P B B
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MPEG Induced Effects
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MPEG Induced Effects
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Adaptation MethodsI-Frame Delay
• Network clogging & buffer overflow drop frames with least importance
• Two parts: tagger & dropper
IFD queue
SSSSWWWW
Outgoing packets
C
Incoming packet
SWW
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Adaptation MethodsSignal-to-Noise Ratio Scalability• Dividing video in layers: one base-layer, several
possible enhancement layers
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Research Categories
• Compressing methods• Adaptation methods• User perceived errors
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Perception ExperimentsMethod
• Double-stimulus continuous quality-scale• 10 sec video sequences• 1 hour per observer
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Perception ExperimentsDesign
• Bitrate: 6 vs. 3 Mbps• Scenes: Matrix - Reloaded vs. Feet of Flames• Duration of loss: 2 vs. 4 vs. 8 sec
• IFD: 1/7 vs. 1/14 B-frame loss• SNR: 1/3 vs. 2/3 base-layer
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Perception ExperimentsQuestions - IFD
• Is leaving out more B-frames (compared to leaving out less B-frames) perceived as worse quality?
• Does the duration of a quality drop influence perceived video quality?
• Do observers notice the difference between the shown bit-rates?
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Perception ExperimentsResults - IFD
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Perception ExperimentsQuestions – SNR Scalability
• Does the duration of a quality drop influence perceived video quality?
• Does a quality saturation effect really show? Do observers really not notice when video quality is enhanced once a certain level is reached?
• Do observers notice the difference between the shown bit-rates?
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Perception ExperimentsResults – SNR Scalability
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Summary
• Saturation effect – when perceived quality is already low/high, observers don’t notice
further decreasing/increasing of the objective quality– thresholds depend on scene content
• IFD– effects were small, but B-frame loss was small – influence of duration and amount of quality loss depends on
scene content and bit-rate – B-frame loss is more pronounced and lasts longer differences
between reference and modified video sequences seem easier to detect
• SNR– observers perceive the different bit-rates of the base-layers – extent depends on scene content and duration of the quality drop
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Future Research Questions
• Influence of the content’s typesemantic versus physical appearance?
predictability versus unpredictability?
• Management of the disturbances or the type of perceived disturbances?
• What about audio?