CDA File Documentation

Summary

A CD Audio track file (.cda) is not music. It is a tiny 44-byte shortcut that Windows shows for each track on an audio CD, and it holds no sound — only a pointer to where the track starts on the physical disc. Copying .cda files to a hard drive copies just the pointers, so they will not play off the disc. To keep the music you must “rip” the CD, converting each track to a real WAV, FLAC or MP3 file with Windows Media Player, iTunes or VLC. Its MIME type is application/x-cdf.

Technical details

FeatureValue
Full nameCD Audio track shortcut
File extension.cda
MIME typeapplication/x-cdf
Format typeTrack pointer / index — contains no audio data
ContainerRIFF, form type CDDA
File size44 bytes (fixed)
DeveloperMicrosoft (Windows representation of Red Book CD audio)
IntroducedWindows 95 era
Underlying standardRed Book (IEC 60908) CD Digital Audio
Audio on disc16-bit PCM, 44,100 Hz, stereo (1,411 kbit/s)
Byte orderLittle-endian (RIFF)
Magic number52 49 46 46 (“RIFF”) at offset 0; CDDA at offset 8
StoresTrack number, start offset (in CD frames), length
Frame rate75 CD frames per second
Playable when copiedNo — audio stays on the disc
Related extensions.wav, .aiff, .flac, .mp3, .cue, .bin
File signature (magic bytes)
52 49 46 46 … 43 44 44 41

Offset 0 reads RIFF and offset 8 reads CDDA. A .cda is a 44-byte RIFF file whose form type is CDDA rather than the WAVE used by a WAV file. The single fmt chunk holds only track metadata: the track number, the track’s start position on the disc as a frame offset (75 frames per second), and its length. There is no data chunk and no audio — the samples live in the CD’s Red Book pressing, and the .cda is only a Windows-generated pointer to them.

What is a CDA file?

A .cda (“CD Audio”) file is one of the most misunderstood items in Windows. When you put a music CD into the drive, File Explorer shows Track01.cda, Track02.cda and so on — but those are not the songs. An audio CD does not store its music as files at all. It follows the Red Book standard (IEC 60908), which stores sound as a continuous stream of raw PCM samples laid out in the disc’s track structure, with no filesystem of audio files. Windows invents a small .cda “file” for each track purely so you have something clickable in Explorer. Each one is exactly 44 bytes and holds only a description of where a track sits on the disc.

The practical consequence catches almost everyone: if you drag the .cda files off the CD onto your hard drive, you copy only the 44-byte pointers. The audio they referenced is still on the disc you just removed, so the copied files will not play. A .cda is meaningful only while the CD is in the drive. To keep the music you have to rip the CD, which reads the PCM off the disc and writes it into a real, self-contained audio file.

The RIFF/CDDA structure of the 44 bytes

A .cda is a RIFF file, the same generic Microsoft container used by WAV, AVI and other formats. RIFF wraps everything in typed “chunks”, each with a four-character ID and a length. What makes a .cda different from a WAV is its form type: where a WAV declares WAVE, a CD-audio stub declares CDDA.

offset  bytes  field
  0      4     "RIFF"                 chunk ID
  4      4     chunk size (little-endian)
  8      4     "CDDA"                 form type (not "WAVE")
 12      4     "fmt "                 format chunk ID
 16      4     fmt chunk size = 24
 20      2     CDDA version (= 1)
 22      2     track number
 24      4     disc serial / track ID
 28      4     start offset, in CD frames (75 frames/second)
 32      4     start offset, in frames (alternate)
 36      4     track length, in frames
 40      4     track length, in frames

Every multi-byte value is little-endian. The key fields are the track number, the start offset expressed in CD frames (a CD runs at 75 frames per second, so a frame is 1/75 of a second), and the track length. Crucially there is no data chunk. A WAV of the same track would carry a data chunk holding megabytes of PCM samples; the .cda carries none. It is a 44-byte index entry, and nothing else.

Why a copied CDA will not play

Because the .cda holds only a frame offset into a specific disc, it is useless the moment that disc is gone. Double-clicking a .cda while the CD is in the drive tells your default player to seek to that frame offset on the disc and start playing — the player reads the audio from the CD, not from the file. Remove the disc, and the offset points at nothing. This is also why emailing or uploading a .cda is pointless: the recipient gets a 44-byte pointer to a disc they do not have.

Ripping: turning a CD track into a real audio file

“Converting a .cda to MP3” is a contradiction, because the .cda contains no audio to convert. What people actually want is to rip the CD: read the PCM samples off the disc and encode them into a real file. That is why every audio tool that handles CDs works by reading the disc, never the lone .cda.

  • Windows Media Player — insert the CD, click Rip CD, and choose a format (MP3 or lossless WAV) and bitrate.
  • VLC — Media › Open Disc to play, or Media › Convert/Save › Disc to rip to MP3, FLAC or WAV.
  • iTunes / Apple Music — insert the disc and confirm Import to encode to AAC, ALAC or MP3.
  • Exact Audio Copy (Windows) or XLD (Mac) — error-corrected, bit-perfect ripping to WAV or FLAC for accuracy.

The format you choose is a quality-versus-size trade-off. A WAV is the raw, uncompressed CD audio — a bit-perfect copy at roughly 10 MB per minute. FLAC is lossless but compressed to about half that size. MP3 and AAC are lossy: much smaller, with a small, usually inaudible quality cost. Accurate rippers such as Exact Audio Copy can additionally emit a single disc image plus a .cue sheet that marks the track boundaries, which preserves gapless albums.

CDA versus WAV and MP3

The difference is not quality but substance. A WAV or an MP3 contains the audio and plays anywhere, on any device, forever. A .cda contains no audio at all — it only references a track on a disc that must be present in a drive. WAV and CDA even share the RIFF container, which is why they look superficially similar, but the CDDA form type and the missing data chunk give it away. Ripping is precisely the act of reading the disc that a .cda points to and writing those samples into a WAV or MP3 that stands on its own.

Frequently asked questions

Why won’t my CDA files play after I copied them from the CD?

Because you copied only the 44-byte pointers, not the sound. The audio stays on the physical disc. Put the CD back in the drive and rip it to WAV, FLAC or MP3 to get files that play on their own.

Why is a CDA file always exactly 44 bytes?

It is a fixed-size RIFF header describing one track: a RIFF/CDDA identifier plus a single fmt chunk of track number, start offset and length. With no data chunk to hold samples, there is nothing else to store, so every .cda is the same tiny size regardless of how long the track is.

How do I convert a CDA to MP3?

You do not convert the .cda itself — you rip the CD track it points to. Insert the disc, open Windows Media Player and click Rip CD (choose MP3), or use VLC’s Convert/Save. No online “CDA to MP3” converter can help, because a lone .cda holds no audio to upload.

References