Method and apparatus for detecting quality defects in a video bitstream

An apparatus for obtaining a quality score for a video sequence represented by a video bitstream, the video sequence comprising a plurality of pictures, the apparatus comprising:

• a receiver for receiving the video bitstream;
• and
• a data processing unit coupled to the receiver, wherein the apparatus is configured to:
• determine a measure of quantization parameter (QP) for at least three of the plurality of pictures of the video sequence, wherein the determining the measure of QP for at least the three pictures of the video sequence comprises:
• determining an average QP for a first picture of the video sequence, determining an average QP for a second picture of the video sequence, and determining an average QP for a third picture of the video sequence;
• detect an abrupt change in the measure of QP, wherein detecting the abrupt change in the measure of QP comprises determining that:
• a) the average QP for the first picture of the video sequence is greater than the average QP for the second picture of the video sequence by at least a first threshold amount t1 and b) the average QP for the first picture of the video sequence is greater than the average QP for the third picture of the video sequence by at least a second threshold amount t2;
• determine whether the detected abrupt change in the measure of QP is part of a scene change;
• identify intra picture flicker as a result of i) detecting the abrupt change in the measure of QP and ii) determining that the detected abrupt change is not determined to be part of a scene change, wherein identifying the intra picture flicker comprises generating a defect indicator indicating that intra picture flicker has been identified;
• and
• after generating the defect indicator, calculate the quality score for the video sequence using a quality model and the defect indicator indicating that intra picture flicker has been identified.

A computer program product comprising a non-transitory computer readable medium storing instructions for obtaining a quality score for a video sequence represented by a video bitstream, the video sequence comprising a plurality of pictures, the instructions comprising:

• instructions for determining a measure of quantization parameter (QP) for at least three of the plurality of pictures of the video sequence, wherein the determining the measure of QP for at least the three pictures of the video sequence comprises:
• determining an average QP for a first picture of the video sequence, determining an average QP for a second picture of the video sequence, and determining an average QP for a third picture of the video sequence;
• instructions for detecting an abrupt change in the measure of QP, wherein detecting the abrupt change in the measure of QP comprises determining that:
• a) the average QP for the first picture of the video sequence is greater than the average QP for the second picture of the video sequence by at least a first threshold amount t1 and b) the average QP for the first picture of the video sequence is greater than the average QP for the third picture of the video sequence by at least a second threshold amount t2;
• instructions for determining whether the detected abrupt change in the measure of QP is part of a scene change;
• instructions for identifying intra picture flicker as a result of i) detecting the abrupt change in the measure of QP and ii) determining that the detected abrupt change is not part of a scene change, wherein identifying the intra picture flicker comprises generating a defect indicator indicating that intra picture flicker has been identified;
• and
• instructions for calculating the quality score for the video sequence using a quality model and the defect indicator indicating that intra picture flicker has been identified.