1. A method comprising: identifying a plurality of video segments having closed caption data corresponding to a phrase, the plurality of video segments associated with respective ones of a plurality of audio data segments; computing a plurality of difference metrics between a baseline audio data segment associated with the phrase and respective ones of the plurality of audio data segments; selecting a set of the plurality of audio data segments based on the plurality of difference metrics; identifying a first one of the audio data segments in the set as a representative audio data segment; determining a first phonetic transcription of the representative audio data segment; and adding the first phonetic transcription to a speech recognition library when the first phonetic transcription differs from a second phonetic transcription associated with the phrase in the speech recognition library.