8. The method of claim 1 , further comprising determining the audio-visual dictionary by: receiving a set of training video clips, each including a temporal sequence of video frames and a corresponding audio soundtrack; generating a set of visual features including visual foreground features and visual background features from the video frames in the set of training video clips; generating a set of audio features including audio foreground features and audio background features from the audio soundtracks in the set of training video clips; computing temporal audio-visual correlations between the visual features and audio features; generating a set of audio-visual grouplets based upon the temporal audio-visual correlations; and forming the audio-visual dictionary including the set of audio-visual grouplets, together with the visual foreground features, visual background features, audio foreground features and audio background features associated with the audio-visual grouplets.
8. The method of claim 1 , further comprising determining the audio-visual dictionary by: receiving a set of training video clips, each including a temporal sequence of video frames and a corresponding audio soundtrack; generating a set of visual features including visual foreground features and visual background features from the video frames in the set of training video clips; generating a set of audio features including audio foreground features and audio background features from the audio soundtracks in the set of training video clips; computing temporal audio-visual correlations between the visual features and audio features; generating a set of audio-visual grouplets based upon the temporal audio-visual correlations; and forming the audio-visual dictionary including the set of audio-visual grouplets, together with the visual foreground features, visual background features, audio foreground features and audio background features associated with the audio-visual grouplets. 13. The method of claim 8 , wherein the temporal audio-visual correlations include correlations between the visual foreground features and the audio foreground features; correlations between the visual foreground features and the audio background features, correlations between the visual background features and the audio foreground features, or correlations between the visual background features and the audio background features.