Gapless playback is common with compact discs, gramophone records, or tapes, but is not always available with other formats that employ compressed digital audio.
Various software, firmware, and hardware components may add up to 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 two decoded pieces of audio must be fed to the hardware continuously over the transition, as if the tracks were concatenated in software.
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.
[1] 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.
For some audio formats (e.g. Ogg Vorbis), where the start and end are precisely defined, the padding is implicitly trimmed off in the decoding process.
Disc at once (DAO) mode allows recording the entire CD in one continuous session, without any pauses between tracks.
For example, crossfading is inappropriate for files that are already gapless, in which case the transition may feel artificially short and disturb the rhythm.
Compared to precise gapless playback, these methods are a different approach to erroneous silence in audio files, but other required features are the same.
A common workaround is to encode consecutive tracks as one single file, relying on cue sheets (or something similar) for navigation.