16. The computer-readable medium of claim 15 , wherein comparing the monophonic melody line extracted from the audio channel of the data encoding the sounds produced by the human voice with the one or more monophonic melody lines of the candidate videos of the subset comprises: selecting, from among a collection of videos, the set of candidate videos that are each (i) identified as being associated with the particular song, and (ii) are classified as a cappella video recordings; extracting, from each of the candidate videos of the set that (i) are identified as being associated with the particular song, and (ii) are classified as a cappella video recordings, a monophonic melody line from an audio channel of the candidate video; selecting, from among the set of candidate videos that are each (i) identified as being associated with the particular song, and (ii) are classified as a cappella video recordings, the subset of candidate videos based on a similarity of the monophonic melody lines of the candidate videos of the subset with each other; and providing, to the recognizer that recognizes songs from sounds produced by a human voice, one or more of the monophonic melody lines of the candidate videos of the subset.
16. The computer-readable medium of claim 15 , wherein comparing the monophonic melody line extracted from the audio channel of the data encoding the sounds produced by the human voice with the one or more monophonic melody lines of the candidate videos of the subset comprises: selecting, from among a collection of videos, the set of candidate videos that are each (i) identified as being associated with the particular song, and (ii) are classified as a cappella video recordings; extracting, from each of the candidate videos of the set that (i) are identified as being associated with the particular song, and (ii) are classified as a cappella video recordings, a monophonic melody line from an audio channel of the candidate video; selecting, from among the set of candidate videos that are each (i) identified as being associated with the particular song, and (ii) are classified as a cappella video recordings, the subset of candidate videos based on a similarity of the monophonic melody lines of the candidate videos of the subset with each other; and providing, to the recognizer that recognizes songs from sounds produced by a human voice, one or more of the monophonic melody lines of the candidate videos of the subset. 17. The computer-readable medium of claim 16 , wherein providing the one or more of the monophonic melody lines of the candidate videos of the subset to the recognizer that recognizes songs from sounds produced by a human voice comprises providing the identifier of the particular song to the recognizer that recognizes songs from sounds produced by a human voice.