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Optical disc recording modes
From Wikipedia, the free encyclopedia
| Optical disc authoring | |
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| Optical media types | |
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| Standards | |
In optical disc authoring, there are multiple modes for recording, including Disc-At-Once, Track-At-Once, and Session-At-Once.
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Disc-At-Once or DAO for CD-R media is a mode that masters the disc contents in one pass, rather than a track at a time as in Track At Once. DAO mode, unlike TAO mode, allows any amount of audio data (or no data at all) to be written in the "pre-gaps" between tracks.
One use of this technique, for example, is to burn track introductions to be played before each track starts. A CD player will generally display a negative time offset counting up to the next track when such pre-gap introductions play. Pre-gap audio before the first track of the CD makes it possible to burn an unnumbered, "hidden" audio track. This track can only be accessed by "rewinding" from the start of the first track, backwards into the pre-gap audio.
DAO recording is also the only way to write data to the unused R-W sub-channels. This allows for extended graphic and text features on an audio CD such as CD+G and CD-Text. It is also the only way to write audio files that link together seamlessly with no gaps, such as The Wall and many mixtape CDs.
Track-At-Once or TAO is a recording mode where the recording laser stops after each track is finished and two run-out blocks are written. One link block and four run-in blocks are written when the next track is recorded. TAO discs can have both data and audio at the same time.
Disc At Once recording for DVD-R media is a mode in which all data is written sequentially to the disc in one uninterrupted recording session. The on-disk contents result in a lead-in area, followed by the data, and closed by a lead-out area. The data is addressable in sectors of 2048 bytes each, with the first sector address being zero. There are no run-out blocks as in CD-R disc-at-once.
Session at Once recording allows multiple sessions to be recorded and finalized on a single disc. The resulting disc can be read by computer drives, but sessions after the first are generally not readable by CD Audio equipment.
- Mike Richter's page on writing modes
- Understanding CD-R & CD-RW by Hugh Bennett