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Understanding Perceived Quality in Transported Video: Key Insights and Future Directions

This study explores the factors affecting perceived video quality during transport, including adaptation methods like I-Frame delay and Signal-to-Noise Ratio (SNR) scalability. Through perception experiments, it evaluates how bitrate, scene content, and duration of quality loss influence viewer experience. Results reveal a saturation effect, where changes in quality become less noticeable at certain thresholds. We identify critical future research questions regarding content semantics and the management of perceived disturbances, aiming to enhance quality in multimedia delivery across various platforms.

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Understanding Perceived Quality in Transported Video: Key Insights and Future Directions

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  1. Perceived Quality for Transported Video Nele Van den Ende Reinder Haakma Maddy Janse Peter van der Stok

  2. Overview • Background • Adaptation Methods • I-Frame Delay • Signal-to-Noise Ratio Scalability • Research Categories • Perception Experiments • Method • Design • Results • Summary • Future Research Questions

  3. Background Access to content, anywhere, anytime

  4. Background But there are disturbance problems…

  5. 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

  6. MPEG Induced Effects

  7. MPEG Induced Effects

  8. Outgoing packets Incoming packet C W W W W W W S S S S S IFD queue Adaptation MethodsI-Frame Delay • Network clogging & buffer overflow drop frames with least importance • Two parts: tagger & dropper

  9. Adaptation MethodsSignal-to-Noise Ratio Scalability • Dividing video in layers: one base-layer, several possible enhancement layers

  10. Research Categories • Compressing methods • Adaptation methods • User perceived errors

  11. Perception ExperimentsMethod • Double-stimulus continuous quality-scale • 10 sec video sequences • 1 hour per observer

  12. 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

  13. 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?

  14. Perception ExperimentsResults - IFD

  15. 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?

  16. Perception ExperimentsResults – SNR Scalability

  17. 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

  18. Future Research Questions • Influence of the content’s type semantic versus physical appearance? predictability versus unpredictability? • Management of the disturbances or the type of perceived disturbances? • What about audio?

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