scope:

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

Four modes are defined to cover a range of use-cases, from monitoring streams where the video payload is fully encrypted through to unencrypted streams, and where there are no limitations on processing power so that deep packet inspection is possible.

The model described is restricted to information provided to it by an appropriate bit stream analysis module or set of modules. The model described here is applicable to progressive download and adaptive streaming, where the quality experienced by the end user is affected by audio-coding and/or video degradations due to coding, spatial re-scaling or variations in video frame rates, as well as delivery degradations due to initial loading delay, stalling (which are both caused by rebuffering at the client), and media adaptations. Here, a "media adaptation" refers to events where the player switches video playback between a known set of media quality levels while adapting to network conditions. Each of the quality levels typically differs in a significant video and/or audio (and thus audiovisual) quality change. These quality changes are most readily observed by changes in bitrate, resolution, frame rate, and similar attributes.

The model predicts a mean opinion score (MOS) on a 5-point absolute category rating (ACR) scale (see [ITU-T P.910]) as a global multi-media MOS score (as defined in [ITU-T P.911], for instance). In addition, the well-defined modules provide several diagnostic outputs.

The primary applications for this model are monitoring of transmission quality for operations and maintenance purposes. The ITU-T P.1203 model for adaptive- and progressive-download-type media streaming may be deployed both in end-point locations and at mid-network monitoring points. Note, however, that the present Recommendation only describes the model that maps input parameters obtained from a probe located at a specific point in the network or in the client to the global multimedia MOS-scores and related quality diagnostic indicators, as described above.

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

Effects such as those due to audio levels, signal noise and effects due to source generation such as video shake or certain colour properties (and other similar video or audio factors) and other impairments related to the payload are not reflected in the scores computed by this model. Therefore, it is possible to have high scores with this model, yet have a poor overall stream quality.

As a consequence, this Recommendation can be used for applications such as:

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

- Benchmarking of different service implementations. However, it cannot be used for direct benchmarking of different encoder implementations.