  This paper studies the quality of multimedia content focusing on 360 video
and ambisonic spatial audio reproduced using a head-mounted display and a
multichannel loudspeaker setup. Encoding parameters following basic video
quality test conditions for 360 videos were selected and a low-bitrate codec
was used for the audio encoder. Three subjective experiments were performed for
the audio, video, and audiovisual respectively. Peak signal-to-noise ratio
(PSNR) and its variants for 360 videos were computed to obtain objective
quality metrics and subsequently correlated with the subjective video scores.
This study shows that a Cross-Format SPSNR-NN has a slightly higher linear and
monotonic correlation over all video sequences. Based on the audiovisual model,
a power model shows a highest correlation between test data and predicted
scores. We concluded that to enable the development of superior predictive
model, a high quality, critical, synchronized audiovisual database is required.
Furthermore, comprehensive assessor training may be beneficial prior to the
testing to improve the assessors' discrimination ability particularly with
respect to multichannel audio reproduction. In order to further improve the
performance of audiovisual quality models for immersive content, in addition to
developing broader and critical audiovisual databases, the subjective testing
methodology needs to be evolved to provide greater resolution and robustness.
