PERCEVAL - Perceptual and Cognitive Quality Evaluation Techniques for Audiovisual Systems, Ulrich...

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PERCEVAL - Perceptual and Cognitive Quality Evaluation Techniques for

Audiovisual Systems

Ulrich Reiterulrich.reiter@ntnu.no

Outline

• PERCEVAL overview• Motivation (long duration)• Method description (long duration)• Experiment (long duration)• Results (long duration)• Conclusions• Food for thought

Ulrich Reiter – PERCEVAL

Outline

Multimedia systems rely on compression and encoding to speed up transmission

As a result, media quality goes down and the audio and video streams can become misaligned

Compression reduces the file size by removing redundant or unessential information

Perceptual consequences of distortion:

- Face identification- Scene/object recognition- Speech comprehension- Audiovisual speech

integration- Temporal order of events

- Audiovisual temporal integration?

- Long duration quality perception?

PERCEVAL project

Outline

Do quality expectations decrease over time and with increased involvement in the content?

How fast can users notice quality changes and at which quality level does this happen?

Is the quality level at which the change is noticed similar to the desired quality level?

Questions to be answered

Quality assessment methods for long duration AV content

SSCQE(Single Stimulus Continuous Quality Evaluation)

Outline

Method description

Quality adjustment

Outline

Experimental conditions

Stimulus material

30min 55sec long

HD resolution (1080p)

H.264/AVC compression – Quantization parameter11 versions, JND

Conversion to 16 bit YUV 4:2:0

Original audio track

Participants22 subjects (8 female, 14 male) in the age of 24-61 years

Test procedure and duration

Experimental procedure

Quality degradation initiated every 3 minsOne JND drop every 10 sec

Outline

Do the quality expectations decrease over time and with increased involvement in the content?

How fast can participants notice quality changes and at which quality level does this happen?

Is the quality level at which the change is noticed similar to the quality level set by the participant?

Questions to be answered

Three subsets of data (20x10 each) created:

1) average quality level of the last minute of each 3min time slot

2) response time to the automatic quality degradationright after the start of each 3 min time slot

3) quality level at the time when a user reacted to quality change

Data preparation

Results for subset data 1)

Main effects plot for quality levels averaged over last minute of each 3 min time section.

Main effects plot for reaction time to quality changes.

Main effects plot for quality levels at time when a userreacted to quality change

Results cont.

Comparison of sensitivity to quality changes underdifferent conditions.

QLRT: Quality Level at Reaction Time

AQL: Absolute Quality Level

Outline

Conclusions

Time dimension does not influence participants’ expectations with respect to the perceived quality. The reaction time to quality changes is relatively constantacross all time intervals.Participants are less sensitive to quality changes when the process is controlled externally than when they are in charge of the quality adjustment.

Outline

Food for thought• Content dependency

– Ideal bandwidth trade-off for audio vs. video quality depends on content type

• Impact of emotional state, fatigue– On perceived quality, on quality requirements / expectations– Use of EEG and body sensors

• Data analysis of non-traditional data– E.g. quantitative and qualitative, combined– Multivariate statistical methods

Thanks for your attention!ulrich.reiter@ntnu.no

References

[1] http://perceval.no[2] ITU-R Recommendation BT.500-7: Methodology for the Subjective Assessment of the Quality of Television Pictures. International Telecommunication Union, Geneva (1996)[3] N. Staelens, S. Moens, W. Van den Broeck, I. Marien, B. Vermuelen, P. Lambert, R. Van de Walle and P. Demeester, “Assessing Quality of Experience of IPTV and Video on Demand Services in Real-Life Environments”, IEEE Transactions on Broadcasting, Vol.56, No.4, Dec. 2010.[4] Borowiak, A., Reiter, U., Svensson, U.P.: Quality Evaluation of Long Duration Audiovisual Content. In: The 9th Annual IEEE Consumer Communications and Networking Conference –Special Session on Quality of Experience (QoE) for Multimedia Communications, pp. 353--357, Las Vegas (2012)[5] Yang, X., Tan, Y., Ling, N.: Rate control for H.264 with two-step quantization parameter determination but single-pass encoding. In: EURASIP Journal on Applied Signal Processing, pp. 1--13, (2006)[6] Wang, H., Qian, X., Liu, G.: Inter Mode Decision Based on Just Noticeable Difference Profile. In: Proceedings of 2010 IEEE 17th International Conference on Image Processing, Hong Kong (2010)Thanks to Adam Borowiak and Ragnhild Eg for providing figures and slides!

PERCEVAL - Perceptual and Cognitive Quality Evaluation Techniques for Audiovisual Systems, Ulrich...

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