8. A computer-implemented method comprising: under control of one or more computing devices configured with specific computer-executable instructions, generating a first score based at least partly on a likelihood that a frame, of a window of sequential frames of audio data, comprises audio data corresponding to a keyword, wherein the window comprises the frame and an equal quantity of (1) frames before the frame and (2) frames after the frame; generating a second score based at least partly on a likelihood that the frame comprises audio data corresponding to background audio; determining a difference between the first score and the second score; and determining that the frame corresponds to an end of the keyword based at least partly on the difference being greater than differences determined for the frames before the frame, and differences determined for the frames after the frame.
8. A computer-implemented method comprising: under control of one or more computing devices configured with specific computer-executable instructions, generating a first score based at least partly on a likelihood that a frame, of a window of sequential frames of audio data, comprises audio data corresponding to a keyword, wherein the window comprises the frame and an equal quantity of (1) frames before the frame and (2) frames after the frame; generating a second score based at least partly on a likelihood that the frame comprises audio data corresponding to background audio; determining a difference between the first score and the second score; and determining that the frame corresponds to an end of the keyword based at least partly on the difference being greater than differences determined for the frames before the frame, and differences determined for the frames after the frame. 10. The computer-implemented method of claim 8 , further comprising determining a size of the window based at least partly on an expected length of time for the keyword to be uttered.