Bitstream-Based Model Standard for 4K/UHD: ITU-T P.1204.3 — Model Details, Evaluation, Analysis and Open Source Implementation

摘要

With the increasing requirement of users to view high-quality videos with a constrained bandwidth, typically realized using HTTP-based adaptive streaming, it becomes more and more important to determine the quality of the encoded videos accurately, to assess and possibly optimize the overall streaming quality. In this paper, we describe a bitstream-based no-reference video quality model developed as part of the latest model-development competition conducted by ITU-T Study Group 12 and the Video Quality Experts Group (VQEG), “P.NATS Phase 2”. It is now part of the new P.1204 series of Recommendations as P.1204.3. It can be applied to bitstreams encoded with H.264/AVC, HEVC and VP9, using various encoding options, including resolution, bitrate, framerate and typical encoder settings such as number of passes, rate control variants and speeds. The proposed model follows an ensemble-modelling-inspired approach with weighted parametric and machine-learning parts to efficiently leverage the performance of both approaches. The paper provides details about the general approach to modelling, the features used and the final feature aggregation. The model creates per-segment and per-second video quality scores on the 5-point Absolute Category Rating scale, and is applicable to segments of 5–10 seconds duration. It covers both PC/TV and mobile/tablet viewing scenarios. We outline the databases on which the model was trained and validated as part of the competition, and perform an additional evaluation using a total of four independently created databases, where resolutions varied from 360p to 2160p, and frame rates from 15–60fps, using realistic coding and bitrate settings. We found that the model performs well on the independent dataset, with a Pearson correlation of 0.942 and an RMSE of 0.42. We also provide an open-source reference implementation of the described P.1204.3 model, as well as the multi-codec bitstream parser required to extract the input data, which is not part of the standard.