methods and apparatus to monitor audio / visual content from various sources are disclosed . an example method disclosed herein comprises determining first information based on a video signal corresponding to monitored media content , determining second information based on an audio signal corresponding to the monitored media content , and identifying a selected one of a plurality of media content sources based on a decision tree comprising a plurality of decision nodes , a first decision node of the decision tree corresponding to a first classification decision resulting from processing at least one of the first information or second information , and a second decision node of the decision tree corresponding to a second classification decision resulting from processing at least one of the first information or second information , the second decision node of the decision tree being selected for evaluation based on an outcome of evaluating the first decision node of the decision tree .