7. The method of claim 1 , wherein the audio-visual dictionary is determined by: receiving training video clips, each including a temporal sequence of video frames and a corresponding audio soundtrack; generating visual features including visual foreground features and visual background features from the video frames in the set of training video clips; generating audio features including audio foreground features and audio background features from the audio soundtracks in the training video clips; computing temporal audio-visual correlations between the visual features and audio features; generating audio-visual grouplets based upon the temporal audio-visual correlations; and forming the audio-visual dictionary including the audio-visual grouplets, together with the visual foreground features, the visual background features, the audio foreground features, and the audio background features associated with the audio-visual grouplets.
20. The method of claim 7 , wherein each of the audio foreground codewords is from an audio foreground vocabulary that is generated based upon the audio foreground content from the audio soundtracks of the plurality of training video clips.