Next generation codecs, benchmarked by the H.264/AVC standard, are providing substantial compression efficiency for the coding and transmission of video. Coupled with technologies offering larger transmission bandwidths over DSL, wireless and satellite networks, the capability of delivering high quality video services to the home is now a reality. The perceptual quality of the content delivered over communications networks will be crucial in ensuring a first-class customer experience. It is therefore important to assess the advantages and disadvantages of the optional features offered by next generation codecs. This paper describes a subjective assessment that was carried out to investigate the perceptual effects of switching the in loop de-blocking filter within the H.264/ AVC CODEC on or off. Although the filter is believed to substantially improve the perceptual quality of video, it has been suggested that in some cases negative perceptual effects can be produced. The H.264/AVC architecture allows de-blocking to be switched off in cases where there are limited processing resources or it is considered a negative perceptual effect may be introduced. This paper describes a study that examined the perceptual effects of de-blocking by employing a standardised subjective assessment methodology. The Absolute Category Rating (ACR) method was used to capture Difference Mean Opinion Scores (DMOS) for a range of video. Content was selected to span a wide and representative range of coding complexity. This content was then encoded at a variety of bit-rates to represent high, medium and low qualities. Results were used to examine the end-user perception of video quality when the de-blocking filter is switched on or off. The experimental design allowed the overall effects of the de-blocking filter to be examined and additionally the relationship between content and quality on the filter performance. The experiment found that the performance of the de-blocking filter was content-dependent. Results were used to discuss the advantages and disadvantages of in-loop de-blocking and there is an examination of content properties (e.g. spatial and temporal complexity) that influence the performance of de-blocking.

The Video Quality Experts Group (VQEG) is preparing a programme of subjective multimedia quality tests. The results from these tests will be used to evaluate the performance of competing objective multimedia quality metrics. The reliability of the subjective test data is of great importance for VQEG's task. This paper provides an overview of VQEG's multimedia ad-hoc group. The work of this group will require subjective tests to be performed by laboratories located in Europe, Asia and North America. For VQEG's multimedia work to be successful, the subjective assessment methodology must be precisely defined and produce reliable and repeatable subjective quality data. Although international standards covering multimedia quality assessment methods are in force, there remains some uncertainty regarding the most effective approach to assessing the subjective quality of multimedia. A review of existing methods is provided. Two experiments are presented investigating the suitability of alternative subjective assessment methods (single-stimulus ACR and SAMVIQ). The results of these experiments are discussed within the context of the VQEG multimedia testing programme.