1. A method comprising: storing, in a file, audio data and metadata describing characteristics of the audio data; wherein the audio data is a digital encoding of audio in a particular audio encoding format; wherein the audio data comprises a stream of sample frames representing the digital encoding of the audio; wherein the metadata specifies: a number of sample frames at the beginning of the stream that are silent sample frames, a number of sample frames at the end of the stream that are silent sample frames, and a first value that indicates whether the particular audio encoding format is a constant bit rate or variable bit rate audio encoding format, and a second value that indicates whether the particular audio encoding format is a constant frame rate or variable frame rate audio encoding format; wherein the method is performed by one or more computing devices.