A device, computer program product and a method, the method may include: extracting a first size information about sizes of different frames of a first segment of an encrypted first streaming media flow that has a first constant bit rate (CBR); extracting second size information about sizes of different frames of a second segment of a second streaming media flow that has a second CBR; and determining a relationship between qualities of the first and second streaming media flows based on the first and second size information; wherein the extracting of the first and second size information and the determining of the relationship are executed without decrypting the first and second encrypted streaming media flows.