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.
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. 14. The method of claim 7 , wherein the temporal audio-visual correlations between the visual features and audio features are statistical temporal causalities.