This book provides an in-depth investigation of the quality relevant perceptual video space in the domain of videotelephony. The author presents an extensive investigation and quality modeling of the underlying video quality dimensions and the overall quality. The author examines the underlying quality dimensions and describes a method for subjective evaluation as well as the instrumental estimation of video quality in videotelephony. The book presents a new subjective test method in the field of video quality assessment. Further, it explains the experimental examination of the underlying video quality dimensions and the subjective-based, as well as instrumental-based quality estimation. Provides an investigation of the underlying quality dimensions of video in videotelephony; Presents insights into a new subjective test method, standardized as ITU-T Rec. P.918; Includes insights into the subjective and instrumental video quality estimation.