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QoS Impact on User Perception
    and Understanding of                         • Introduction
   Multimedia Video Clips                        • Approach
                                                 • Results
         G. Ghinea and J.P. Thomas
                                                 • Conclusions
       Department of Computer Science
         University of Reading, U.K.

     Proceedings of ACM Multimedia Conference
                   November 1998

Introduction                                     Goal
• QoS deals with delay and jitter                • Look at correlation between comprehension
  à But these ignore the human element             and QoS parameters
• Human element work has looked at:                 – Frame rate for now
  • Thresholds beyond which no improvement to    • Analyze through user studies
    users                                           – Show clips to a bunch of people
  • Synchronization limits for audio and video         + Vary frame rate

• Human element work has not looked at:             – Get PQ scores
  • Capacity to understand                          – Ask questions to ascertain comprehension
  • Ability to analyze informational content

User Studies                                     User Studies
• Show movie clips to users                      • Users told:
  – MPEG-1 (352x288 pixels)                         – Don’t let personal bias to movie influence PQ
  – 31-45 seconds long                              – Do see if general MM QoS would satisfy the clip
• Users told to wear glasses (if appropriate)    • Specifically, users told to look at:
                                                    – Clarity and acceptability of audio
                                                    – Lip synchronization during speech
                                                    – General relationship between visual and audio
                                                      message components

                                              Considerations in Movie
• Fixed:                                      • Spatial parameters or Temporal parameters
   – Color depth                                – (Assume one or the other)
   – Window size                                – (Called it “Dynamic”)
   – Audio always present                     • Importance of audio information
      + Even at low bandwidth, can do audio
                                              • Importance of video parameters
• Varied:                                     • Importance of textual information
   – Frame rate: 5, 15, 25
      + But kept same for each user
                                              • Assign weights on a scale of 0-2 for each
      + 10 users at each rate
   – Movie categories (next slide)

Groupwork                                     Video Categories
• Consider movies:
   – Action movie        - Choir
   – Cartoon             - Commercial
   – Cooking             - Weather
• Rate 0-2:
   – Dynamic
   – Audio importance
   – Video importance
   – Text importance
• (Don’t peek)                                      (How many possible “categories”?)

Instructions                                  Outline
• Watch clip                                  • Introduction
• Window close                                • Approach
• Ask questions                               • Results
• Rate clip for PQ: 1 (worst) to 6 (best)     • Conclusions

Overall Results                                  Visual Information Results

• Frame rate doesn’t matter for comprehension    • Lowest correct answers to action, rugby, pop
    – “Dropping” doesn’t affect understanding       – Frame rate doesn’t matter
    – (On the order of seconds, probably)           – “Enjoying music”, say, so miss information

Audio Information Results                        Qualitative Results
                                                 • Snooker video
                                                    – “What color was the pocketed ball?”
                                                    – ‘Red’ ball looked brown
                                                    – Those that watched, saw ‘Red’ score points
                                                 • Commercial video (bathroom cleanser)
                                                    – “Was the couple married?”
                                                    – Couple was married, clue was ring
                                                    – Users thought because of dialog and topic
• Users missed more audio queues                 • Cooking video
    – In rugby, watching the action                 – “Were there forks?”
    – In pop, missed questions on lyrics            – Yes, but not in a normal way … large on wall
                                                    – Only 30% got it right for real reason

Perceptual Quality Results                       Conclusion
                                                 • User QoS is based on PQ plus understanding
• Lower the frame rate, lower the quality        • Frame rate not proportional to understanding
    – Not linear                                 • Absorbing audio, video and text at the same
                                                   time is difficult
• Enjoyment does not always match answering         – Deliver messages in parallel
    the questions correctly
                                                 • Relationship between PQ and understanding
•   Action got high quality                        is complex
•   News got only average                        • Highly dynamic scenes have a negative
    – Lip synch missing                            impact on understanding
• Pop varied with frame rate                        – But entertainment level the same
    – “Rich” media, maybe entertainment, needs   • QoS needs
      bandwidth                                     – PQ and understanding, too

My Conclusions                                  Evaluation of Science?
• I want to see the questions!                  • Category of Paper
• Trick seems to be to make the questions all   • Science Evaluation (1-10)?
  equal for each movie type                     • Space devoted to Experiments?
• Comparison of text across all types?


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