scope:

This Recommendation describes a set of objective video quality assessment modules that together with audio and integration modules can be used to form a complete model to predict the impact of audio and video media encodings and observed Internet protocol (IP) network impairments on quality experienced by the end-user in multimedia streaming applications. The streaming techniques addressed comprise progressive download as well as adaptive streaming, for both mobile and fixed network streaming applications. The video quality modules can also be used stand-alone as a video quality prediction model.

Five model types are defined to cover a range of use-cases, from monitoring bitstreams where the video payload is fully encrypted, unencrypted bitstreams, and where deep packet inspection is possible, or where the bitstream is available at the encoding premises up to measurement using the pixel information available e.g., from the client side. The models thus have a wide range of applications, from encoding optimization over client-side quality of experience (QoE) assessment to network or service optimization, or benchmarking purposes. The models in the [ITU-T P.1204] series of Recommendations are bitstream based, pixel-based and hybrid based.

The models described here are applicable to progressive download and adaptive streaming or other streaming applications with reliable transport, where the quality experienced by the end user is affected by video degradations due to coding, spatial re-scaling, or variations in video frame rates. Quality assessment of adaptive streaming includes aspects of media adaptation, which may be handled in integration modules such as [ITU-T P.1203.3], and not in the video modules. This Recommendation is able to handle various video codecs (i.e., [ITU-T H.264], [ITU-T H.265] highefficiency video coding (HEVC), video payload type 9 (VP9), AOMedia Video 1 (AV1)¹ , resolutions up to 4K or ultra-high definition-1 (UHD-1) and frame rates of up to 60 frames/s. The video-quality module Pv of [b-ITU-T P.1203], i.e., [ITU-T P.1203.1], only addresses [ITU-T H.264] and full high definition (HD) with up to 30 frames/s.

The models predict a mean opinion score (MOS) on a five-point absolute category rating (ACR) scale (see [ITU-T P.910]) as an overall video quality MOS (5 to 10 s). In addition to the overall quality score, the video quality models produce a per-one-second quality score, suitable for diagnostics or integration into an integral quality score for longer sessions (cf. e.g., [ITU-T P.1203.3] for 1 to 5 minute duration sessions).

The models associated with this Recommendation cannot provide a comprehensive evaluation of the video quality as perceived by an individual end-user because the scores reflect the perceived impairments due to the coded video media data being transmitted over an IP connection with a certain performance and do not include a specific terminal device or user-specific information. The scores predicted by such a general quality model necessarily reflect average perceptual quality.

Effects due to source generations such as signal noise, video shake, certain colour properties (and other similar video factors), as well as other impairments related to the payload are not reflected in the scores computed by this model.

As a consequence, this Recommendation can be used for applications such as the following.

- In-service quality monitoring for specific IP-based audiovisual services, as specified in more detail in clause 6.1.

- Performance and quality assessment of live networks (including video encoding) considering the effect due to the encoding bitrate, encoding resolution, and encoding frame rate.

- Laboratory testing of video systems.

- Benchmarking of different service implementations.

- Benchmarking of different encoder implementations. Note that only the full/reduced reference pixel-based model type can be used for direct benchmarking of this type. - Evaluation of transcoding solutions.

In particular, targeted applications are progressive download streaming and adaptive streaming (using reliable transport), which includes the following.

- Over-the-top (OTT) services, as well as operator-managed video services (over the transmission control protocol).

- Video over both mobile (MO) and fixed connections.

- The streaming protocols HTTP live streaming (HLS) or dynamic adaptive streaming over HTTP (DASH) used with the hypertext transfer protocol (HTTP) or HTTP2 over TCP/IP or quick user datagram protocol Internet connections (QUIC), or real-time messaging protocol (RTMP) over TCP/IP). Note that the model is agnostic to the specific application or transport layer protocol, with the exception that it assumes reliable delivery of video packets.

- Video services typically use container formats based on the ISO/IEC base media file format such as moving picture experts group-4 (MPEG-4) part 14 (MP4), or other container formats such as audio video interleave (AVI), matroska video (MKV), WebM, third generation partnership (3GP), and MPEG-2 transport stream (MPEG-2-TS). Note that the model is agnostic to the type of container format.

¹ AV1 codec is currently supported by [ITU-T P.1204.4] and [ITU-T P.1204.5].