EVALUATION OF SUBJECTIVE VIDEO QUALITY ON MOBILE DEVICESJukka Häkkinen {@helsinki.fi, University of Helsinki and Nokia Research}

Satu Jumisko-Pyykkö {@tut.fi, Tampere University of Technology}

ABSTRACTSubjectively perceived video quality is a critical factor when adopting new mobile video

applications. When video is used in mobile networks the most important requirements are related to low bitrates, framerates and the screen size of mobile device. In two tests we investigated the effects of codecs and combinations of audio and video streams with low bitrates and different contents on the perceived video quality of mobile devices. The first test showed that the codec H.264 produced the most satisfying video quality, but the quality was not high enough for the presentation of textual information. In the second test, the audio-video ratio 32/128kbps was found to be the most pleasant, but there were content dependent variations.

THE AUDIO-VIDEO STUDYThe optimal audio-video bitrate ratio

RESEARCH METHOD Participants: 60 (18-65 years) stratified by age, gender, <20% professionals

Test procedure Single stimulus method (ITU-R T.500-11)

Pre-test: Sensory tests, demographic surveyTest: Anchoring, training, actual testPost-test: Content survey, interview

ContentsPotential for mobile TV, popularSpatial and temporal resolution

Parameters

RESULTS The highest quality score given for the ratio 32/128kbps

DISCUSSION AND CONCLUSIONSAudio and video ratios were strongly dependant on contents.Content dependant requirements are necessary to take into account for bandwidth optimization to deliver acceptable quality in new products such as mobile television.

THE VIDEO STUDYThe most satisfying codec for visual quality

RESEARCH METHOD Participants: 75 (18-65 years) stratified by age, gender, <20% professionals

Test procedure Single stimulus method (ITU-R T.500-11)

Contents

Parameters

RESULTS H.264 the most satisfying (p<0.001)

In tele-text content, not difference between the codecs (p>0.05)

DISCUSSION AND CONCLUSIONS H.264 produces the most satisfying quality for typical TV contents. The quality in details, e.g. text quality is needed to be improved for providing the satisfying quality.

Parameters

Codecs H.263-AACTotal bitrate (kbps) 160Audio bitrate (kbps) 64 32 16

Video bitrate (kbps) 96 128 144Framerate (fps) 12,5Contents 5Device Nokia 7700Picture ratio QCIF

Codecs H.263 Real Video 8 H.264Total bitrate (kbps) 80

Framerate (fps) 12,5Contents 6Device Nokia 6600Picture ratio QCIF

Content AnimationIcehockey

Musicvideo News

TV series

AV-ratio (kbps)

32/128 16/144

32/128, 64/96

64/96 32/128, 16/144