scope:

This Recommendation provides an overview of two recommended objective parametric quality assessment models that predict the impact of observed IP network impairments on quality experienced by the end user in multimedia mobile streaming and IPTV applications over transport formats such as: RTP (over UDP), MPEG2-TS (over UDP or RTP/UDP), 3GPP-PSS (over RTP).

As an umbrella Recommendation, ITU-T P.1201 provides the framework for the actual two algorithmic models described in [ITU-T P.1201.1] and [ITU-T P.1201.2]. These algorithms are aimed at monitoring the audio, video and audiovisual quality of IP-based video services based on packet-header information, with two application areas:

- [ITU-T P.1201.1] specifies the model algorithm for the lower resolution application area, including services such as mobile TV.

- [ITU-T P.1201.2] specifies the model algorithm for the higher resolution application area, including services such as IPTV.

These models are restricted to input information contained in packet headers, prior and static knowledge about the media stream and dynamic buffering information from the client. Information from decoding the bit-stream or parsing the packet payload is not used.

These models predict mean opinion scores (MOS) on a five-point ACR scale (see [ITU-T P.910]) for audio and video parts of the stream, as well as a global audiovisual MOS score (as defined in [ITU-T P.911], for instance).

The primary application for these models is the monitoring of transmission quality during in-service operation or for maintenance purposes. The ITU-T P.1201 model may be deployed both in end-point locations and at mid-network monitoring points. The location of the model and the location of the measurement probe together determine the mode of operation, as described in more detail in clause 6.1.

The primary quality prediction made by such models is not based on the information in the audio and video coding layer (payload) of the stream being analysed, but on information on the payload as it is available from packet headers and additional side-information.

This Recommendation cannot provide a comprehensive evaluation of audiovisual quality as perceived by a particular end user because its scores reflect the impairments due to encoding and the subsequent IP network being assessed, which may only be one part of the end-to-end connection. An explicit inclusion of processing steps, such as content contribution from, for example, satellite networks, display properties, etc., are not considered. Hence, also the effects of audio level, noise, delay (and corresponding similar video factors) and other impairments related to the media payload are not reflected in the scores computed by such a model. Further, the quality impact due to a specific audio or video encoder implementation or a specific decoder-side packet loss concealment implementation is not explicitly addressed. Instead, the models have been developed for a set of dedicated service implementations, which are assumed to be meaningful representations of today's IP-based streaming video services. As a consequence, however, in case of significant deviations of a given service being assessed from the service configurations used for developing this standard, it is possible to obtain high-quality scores with this Recommendation, but yet to have a poor quality of the stream as it is perceived by actual users, or vice versa. Moreover, the scores predicted by a parametric model (i.e., without access to payload information) necessarily reflect a somewhat simplified representation of the perceptual impairment of the considered stream.

However, with only using packet-header information, the models still enable estimation of payloadrelated information, and thus allow to provide valid and, in most cases, accurate predictions, presuming that they are applied in an appropriate manner, following this Recommendation.

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, but only the effect of different encoding bitrates and transmission errors for a given decoder-based packet loss concealment. The implementations that can be assessed with ITU-T P.1201 include the audio and video encoding bitrates, the employed video GOP-structure, frame rate, resolution, potential packet loss and the audio codec type.

The audio model algorithm is considered as a part of ITU-T P.1201 that may be employed in combination with other than the ITU-T P.1201 video model algorithm, for example, with the bitstream-based ITU-T P.1202 model algorithms (ITU-T P.1202-series of Recommendations), or be used as a stand-alone audio model. Consequently, care is taken that the application range for the audio model algorithm is designed to be slightly larger than necessary for a component of an audiovisual model applied to services as considered for the ITU-T P.1201 activity.