What's the sector format on audio CDs?

[Videogamer555]

On data CDs, the structure of a single sector is header, data, footer. The sector contains a time stamp (yes, even on data disks, it references time, rather than number of bytes, because CD hardware is based on time position in the audio, as CDs were originally only audio technology). With data CDs, the complete sector size is 2352 bytes, with the actual payload data taking up only 2048 bytes (and the header and footer together have only 304 bytes total).

So this leaves me with some questions about audio CD sectors. Do they have the same format (header, data, footer) as a data CD, or is the entire sector containing audio data? Is the sector size for audio CDs 2352 bytes, as it is for data CDs?

[El Heggunte]

On data CDs, the structure of a single sector is header, data, footer. The sector contains a time stamp (yes, even on data disks, it references time, rather than number of bytes, because CD hardware is based on time position in the audio, as CDs were originally only audio technology). With data CDs, the complete sector size is 2352 bytes, with the actual payload data taking up only 2048 bytes (and the header and footer together have only 304 bytes total).

So this leaves me with some questions about audio CD sectors. Do they have the same format (header, data, footer) as a data CD, or is the entire sector containing audio data? Is the sector size for audio CDs 2352 bytes, as it is for data CDs?

No and yes.

«On a Red Book audio CD, data is addressed using the MSF scheme, with timecodes expressed in minutes, seconds and another type of frames (mm : ss : ff), where one frame corresponds to 1/75th of a second of audio: 588 pairs of left and right samples. This timecode frame is distinct from the 33-byte channel-data frame described above, and is used for time display and positioning the reading laser. When editing and extracting CD audio, this timecode frame is the smallest addressable time interval for an audio CD; thus, track boundaries only occur on these frame boundaries. Each of these structures contains 98 channel-data frames, totaling 98 × 24 = 2,352 bytes of music. The CD is played at a speed of 75 frames (or sectors) per second, thus 44,100 samples or 176,400 bytes per second.

In the 1990s, CD-ROM and related Digital Audio Extraction (DAE) technology introduced the term sector to refer to each timecode frame, with each sector being identified by a sequential integer number starting at zero, and with tracks aligned on sector boundaries. An audio CD sector corresponds to 2,352 bytes of decoded data. The Red Book does not refer to sectors, nor does it distinguish the corresponding sections of the disc's data stream except as "frames" in the MSF addressing scheme.»

source: https://en.wikipedia.org/wiki/Compact_Disc_Digital_Audio#Frames_and_timecode_frames

[Cornucopia]

Total main channel Sector size is always 2352bytes on a CD.
User data/payload sector size varies:
1. Audio CDs = 2352 (aka ALL of it is used for audio data samples)
2. Mode 1 Data CDs, Mode 2 Form1 Data CDs = 2048 (rest is header/footer w timestamp, mode info, enhanced Error detection/correction info)
3. Mode 2 Form 2 Data CDs = 2324 (rest is header/footer w timestamp, mode info, but NO ED/C) - used in the MPEG tracks of (S)/VCDs, etc.

Note that since all audio CDs use all their main channel bits for audio data, there is no room for timing info. How do they do it?!!
Well, they have a 2nd, very low bitrate channel, called a sub-channel. The data on there is called "sub-code". It is meant to tell you about the Lead-In, Track info, Lead-Out areas and give the time in. On specialty CDs (CDG, CDtext, CD-BMG, CD-Midi, etc) it also has a small space for specialty user data. Total is 96 bytes/sector.
See https://en.wikipedia.org/wiki/Compact_Disc_subcode.

If you need more info, I can tell you most, but if you need a near definitive reference, the best place is a book. I have it (in storage), can't remember what it's called, but it lays out most everything you'd want to know about the CD format. I say MOST, because there were some glaring omissions which I've had to piece together to find out what I know beyond what it tells you.

Scott