Gapless playback

Gapless playback is the uninterrupted playback of consecutive audio tracks, such that relative time distances in the original audio source are preserved over track boundaries on playback. For this to be useful, other artifacts (than timing related) at track boundaries should not be severed either. Gapless playback is common with compact discs, gramophone records, or tapes, but is not always available with other formats that employ compressed digital audio. The absence of gapless playback is a source of annoyance to listeners of music where tracks are meant to segue into each other, such as some classical music (opera in particular), progressive rock, concept albums, electronic music, and live recordings with audience noise between tracks.

Various software, firmware and hardware components may add up a substantial delay associated with starting playback of a track. If not accounted for, the listener is left waiting in silence as the player fetches the next file (see harddisk access time), updates metadata, decodes the whole first block, before having any data to feed the hardware buffer. The gap can be as much as half a second or more — very noticeable in "continuous" music such as certain classical or dance genres. In extreme cases, the hardware is even reset between tracks, creating a very short "click".

To account for the whole chain of delays, the start of the next track should ideally be readily decoded before the currently playing track finishes. The two decoded pieces of audio must be fed to the hardware continuously over the transition, as if the tracks were concatenated in software.

Many older audio players on personal computers do not implement the required buffering to play gapless audio. Some of these rely on third-party gapless audio plug-ins to buffer output. Most recent players and newer versions of old players now support gapless playback directly.

Lossy audio compression schemes that are based on overlapping time/frequency transforms add a small amount of padding silence to the beginning and end of each track. These silences increase the playtime of the compressed audio data. If not trimmed off upon playback, the two silences played consecutively over a track boundary will appear as a pause in the original audio content. Lossless formats are not prone to this problem.

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