1. A method for determining a quality index for a test video sequence, said method comprising: receiving, in a processor, a test video sequence, wherein said test video sequence comprises a first plurality of image values; receiving, in said processor, a reference video sequence corresponding to said test video sequence, wherein said reference video sequence comprises a second plurality of image frames; in said processor, calculating a spatial quality index using said test video sequence and said reference video sequence, wherein said calculating a spatial quality index comprises: calculating a multi-scale structural similarity (MS-SSIM) index for each image frame in said first plurality of image frames and a temporally corresponding image frame in said second plurality of image frames, thereby producing a plurality of MS-SSIM indices; pooling said plurality of MS-SSIM indices, thereby producing a plurality of pooled MS-SSIM indices; determining a minimum value from said plurality of pooled MS-SSIM indices: and setting said spatial quality index to said minimum value; in said processor, calculating a temporal quality index using said test video sequence and said reference video sequence; and in said processor, combining said spatial quality index and said temporal quality index to form a final quality index for said test video sequence.