, Volume 36, Issue 1-2, pp 167-184

“I would like to see the subtitles and the face or at least hear the voice”: Effects of picture ratio and audio–video bitrate ratio on perception of quality in mobile television

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Abstract

In new mobile video applications, the subjectively perceived visual and audiovisual qualities are critical factors in the wide audience adoption of mass products. The critical factors in mobile video coding are related to low bitrates, framerates and screen size of the devices. The first part of this study examined the effects of codecs, bitrates and picture ratio on the perceived visual video quality. In the second study, effects of two audio–video bitrate ratios are presented as factors in the perceived audiovisual video quality and the results are compared to the previous study that showed the content dependency in the audio–video bitrate ratio comparisons. In the results of the visual quality study, H.264 was rated as the most satisfying, but the quality was still not enough for text legibility and perceiving important details of image due to the QCIF picture ratio. The codec XviD was in generally experienced as worse than the H.264, but with the screen size SIF-SP with XviD codec was rated better with several contents. In the audiovisual study, the results also showed that in the low total bitrates the significance of audio is increased. However, the higher and lower bitrates had similar content dependent effects.