【音视频】基于声网实时音视频能力的音视频质量体系建设

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音视频质量评价模型理论","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"质量评估的种类分为两种:","attrs":{}}]},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"主观质量评估:利用人眼作为对象来进行的质量评判和得到MOS分值","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"客观质量评估:利用数学模型,模拟主观质量评估的方法,无需人的介入","attrs":{}}]}]}],"attrs":{}},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"1.1 主观质量评估","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在国际标准中,统一使用MOS值来评价系统接收到的经过压缩后的音视频主观体验。MOS(Mean Opinion 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1.1.1 BT.500标准","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"BT.500标准《电视图像质量的主观评估方法》主要应用于电视图像的质量评估,对主观测试方法进行了以下规定:","attrs":{}}]},{"type":"numberedlist","attrs":{"start":1,"normalizeStart":1},"content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":1,"align":null,"origin":null},"content":[{"type":"text","text":"观察条件:表一列出了BT.1788建议的观测条件,观测距离和水平观测角度BT.500建议如表二","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":2,"align":null,"origin":null},"content":[{"type":"text","text":"源信号:源信号直接提供基准图形以及测试中的系统的输入,源片段的质量应尽可能高。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":3,"align":null,"origin":null},"content":[{"type":"text","text":"测试材料选择:测试场景的数目和类型对解释主观评估的结果而言是至关重要的。对于特定的测试问题需要选择相应的测试材料。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":4,"align":null,"origin":null},"content":[{"type":"text","text":"观测者:观测者的数量应达到15人以上,他们应当不是专家,在某种意义上,他们与图形质量没有直接利害关系,只是作为其日常工作的一部分,并且他们不是经验丰富的评估者。但是对于特殊的测试需求,也可以使用专家观测者。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":5,"align":null,"origin":null},"content":[{"type":"text","text":"评估说明:应仔细向评估者介绍评估方法、损伤类型或可能出现的质量因子、等级评定尺度、时间安排等。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":6,"align":null,"origin":null},"content":[{"type":"text","text":"评估方法","attrs":{}}]}]}]},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":1,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"双刺激损伤尺度(double-stimulus 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information)计算是将视频中每一帧的亮度平面经过Sobel滤波,滤波器是用来提取并集中高频成分,将低频成分过滤掉,再对每一个像素求标准差,进而得到一个时间序列的空域信息,最后这个序列中的最大值用来表达场景内容的空域信息。如果SI值高,表示在一帧内有大量的细节信息,如果该序列是黑屏或者当图像轮廓较为模糊,SI指标会是0。","attrs":{}}]}]}],"attrs":{}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/56/56da5a5c669e0ae828c02e8e188eb364.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"感知信息(temporal perceptual 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