What is a .ac3 file?
Dolby Digital Audio · Audio · Dolby Laboratories · 1991
AC-3 is Dolby Digital, the surround-sound audio format used on DVDs, Blu-rays and digital TV. A .ac3 file holds a multi-channel soundtrack, typically 5.1, compressed for home cinema.
What is a .ac3 file used for?
Dolby Digital frames begin with the sync word 0B 77. AC-3 delivers up to 5.1 channels (five speakers plus a subwoofer) and is the standard cinema and broadcast surround format alongside its successor E-AC-3.
You usually meet AC-3 inside video files rather than on its own. Players like VLC decode it; converting to a stereo format helps on devices without surround support.
What opens a .ac3 file?
The .ac3 format opens in the following apps, grouped by operating system. If one app does not work, try another from the same list.
Windows
- VLC
- foobar2000
- MPC-HC
macOS
- VLC
- IINA
Linux
- VLC
- ffmpeg
- mpv
Open a .ac3 file step by step
- Confirm the file really is a .ac3. Drop it into the WhatFileType identifier, which reads its signature in your browser without uploading anything.
- On Windows, open it with VLC or foobar2000.
- On Mac, use VLC or IINA.
- On Linux, try VLC or ffmpeg.
- Still stuck? Convert the .ac3 to wav, which opens more widely.
Why can't I open my .ac3 file?
Almost always because no installed app understands AC-3. Install one of the apps above, or convert the file to a format your existing software already reads. If double-clicking opens the wrong program instead of nothing at all, the file association is set to the wrong app rather than the file being broken.
The other possibility is that the file is not really a .ac3 at all. Drop it into the file identifier to check it by its bytes instead of its name. Nothing is uploaded.
How to convert a .ac3 file
You can convert a .ac3 file to wav, aac, mp3 using a conversion tool or the export menu of an app that opens it.
What is the .ac3 file signature (magic bytes)?
A .ac3 file starts with the hex bytes 0B 77, which read as .w in ASCII. Programs identify AC-3 by those bytes, not by the filename, so a renamed file still gives itself away.
These are the documented signatures for AC-3. For a full breakdown, see the Dolby Digital (AC-3) file signature page.
| Hex signature | Offset | ASCII | Note |
|---|---|---|---|
| 0B 77 | 0 | .w | sync word |
See the full magic-numbers reference for every format.
Frequently asked questions
What is a .ac3 file?
AC-3 is Dolby Digital, the surround-sound audio format used on DVDs, Blu-rays and digital TV. A .ac3 file holds a multi-channel soundtrack, typically 5.1, compressed for home cinema.
How do I open an AC3 file?
Play it in VLC, which decodes Dolby Digital. To play it on a stereo-only device, convert it to WAV or AAC.
Is AC-3 the same as Dolby Digital?
Yes. AC-3 is the technical name for Dolby Digital, the 5.1 surround format on DVDs, Blu-rays and broadcast TV.
Why is there an .ac3 file with my movie?
It is the surround-sound track, sometimes stored separately from the video. A player combines them, or you can mux it back into the video file.
Related formats
Sources
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