In-Service Performance Metrics for MPEG-2 Video Systems

With the advent of new digital video systems that utilize compression to achieve a savings in transmission or storage bandwidth, the quality of the received output video can be dependent not only upon the inherent spatial and temporal information content of the input video but also upon the dynamic variability of the digital communications channel. Therefore, out-of-service quality measurements using video test signals or scenes may not relate at all to the resultant received quality of actual program material. Furthermore, traditional in-service quality measurements made by injecting test signals into the non-visible portion of the video signal (e.g., the vertical interval in the NTSC or PAL video standard) are not applicable to modern digital video systems. Thus, a new method is required to make in-service video quality measurements on actual program material. This paper describes a new test instrument for measuring the quality of a video transmission or storage system where the input and output of the system may be spatially separated, and when there is no a priori knowledge of the input video. The test instrument makes continuous quality measurements by (1) extracting statistics from sequences of processed input and output video frames, (2) communicating these extracted statistics between the input and the output ends using an ancillary-data channel of arbitrary bandwidth, (3) computing individual video quality parameters from the communicated statistics that are indicative of the various perceptual aspects of video quality (e.g., spatial, temporal, color), and (4) calculating a composite video quality metric by combining the individual video quality parameters. The test instrument makes coarser quality measurements (coarser in the sense that the extracted statistics come from larger spatial-temporal regions) when smaller capacity ancillary-data channels are available and finer quality measurements when larger capacity ancillary-data channels are available. The design goal for the test instrument is to make the most accurate in-service video quality measurements given the available ancillary-data-channel bandwidth (mobile telephone connections, modem connections over the Public Switched Telephone Network (PSTN), Internet connections, Local Area Network (LAN) connections, satellite connections, cable connections, etc.).