scope:

This standard specifies a method for estimating the video performance of a one-way video transmission system, as shown in Figure 1. The objective video performance estimator is defined for the end-to-end transmission quality between the two points shown in the figure. The estimation method is based on processing 8-bit digital component video as defined by ITU-R Recommendation BT.601 (henceforth abbreviated as Rec. 601).¹ The encoder shown in Figure 1 can utilize various compression methods (e.g., MPEG, H.263, NTSC, etc.). The transmission channel may be a simple pass-through for evaluation of a codec (encoder/decoder combination) or may include a concatenation of various compression methods and memory storage devices, but it is assumed that any digital transport involved is error-free. While the derivation of the objective quality estimator described in this standard considered error impairments (e.g., bit errors, dropped packets), independent testing results are not currently available to support the use of the estimator for systems with error impairments.

Purpose

This standard provides a video performance estimation method for one-way compressed video signals transported digitally on an error-free network or storage system. This video performance estimation method is for possible use with end-user systems, carriers, information and enhanced-service providers, and customer premise equipment, provided they introduce no significant error events (e.g., bit errors, dropped packets).

Application

This standard provides estimations for television video classes (TV0-TV3), and multimedia video class (MM4) as defined in ITU-T Recommendation P.911, Annex B. The applications for the General Model described in this standard include but are not limited to:

¹ This does not preclude implementation of the measurement method for one-way video transmission systems that utilize composite video input and outputs. Specification of the conversion between composite and component domains is not part of this standard. For example, SMPTE 170M specifies one method for performing this conversion for NTSC.

1. Codec evaluation, specification, and acceptance testing, consistent with the limited accuracy as described below.

2. Real-time, in-service quality monitoring at the source.

3. Remote destination quality monitoring when a copy of the source is available.

4. Real-time, in-service quality monitoring at the source or destination when an ancillary data channel is available to transmit the extracted feature information (see clauses 4 and 7.1.1).

5. Quality measurement of a storage or transmission system that utilizes video compression and decompression techniques (either a single pass or a concatenation of such techniques).

Alternate standardized quality estimation models may satisfy these applications with similar accuracy. Users of this standard may consult the comparable specifications of the ITU-T and ITU-R.

Limitations

The General Model described in this standard cannot be used to replace subjective testing. Correlations between two carefully designed and executed subjective tests (i.e., in two different laboratories) normally fall within the range 0.92 to 0.97. This standard does not supply a means for quantifying potential errors between subjective assessments of quality and the General Model's estimates. Users of this standard should review the comparison of available subjective and objective results to gain an understanding of the range of video quality rating estimation error.

The General Model should yield acceptable results for multimedia video class MM5 (defined in ITU-T Recommendation P.911, Annex B). However, use of General Model for MM5 video systems is not recommended until further independent validation tests can be performed.

Use of the General Model for video systems with transmission channel errors (e.g., packet loss; see Figure 1) is also not recommended until further independent validation tests can be performed.

The General Model does not provide a comprehensive evaluation of two-way multimedia transmission quality. It only measures the effects of one-way video distortion. The effects of audio distortion, audio delay, video delay, audio-video synchronization, and other impairments related to two-way interaction are not reflected in the General Model scores. Therefore, it is possible to have high General Model scores, yet poor quality of the multimedia connection overall.

¹ This does not preclude implementation of the measurement method for one-way video transmission systems that utilize composite video input and outputs. Specification of the conversion between composite and component domains is not part of this standard. For example, SMPTE 170M specifies one method for performing this conversion for NTSC.