1. A method comprising: storing, in a file, audio data and metadata describing characteristics of the audio data; wherein the audio data comprises a stream of sample frames representing a digital encoding of audio; wherein the audio is digitally encoded in a particular audio encoding format; wherein the metadata specifies at least one of: a number of sample frames at the beginning or the end of the stream that are silent sample frames, or 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.