1. A method comprising: under control of one or more computing devices comprising one or more processors, classifying, by a VAD module, a plurality of frames of a media file into one or more speech frames and one or more non-speech frames; receiving feedback associated with the one or more speech frames and the one or more non-speech frames, the feedback including a determination of accuracy of classifying one or more frames of the media file that are located at a predetermined time before the plurality of frames of the media file or that are selected based on a predetermined condition, the feedback being generated by a speech recognizer, the VAD module and the speech recognizer processing the media file asynchronously; and utilizing the feedback to update a model to be used for voice activity detection (VAD) of a plurality of frames of the media file yet to be processed.
5. A method as recited in claim 1 , wherein the feedback includes a text transcript representing a content of the one or more speech frames.