AVI to AC3 Converter

Extract AC-3 (Dolby Digital) Audio from AVI

This page discards the video track of an AVI and re-encodes its soundtrack as AC-3, the Dolby Digital audio system specified by ATSC as A/52 and used for DVD-Video, digital television and Blu-ray secondary audio. The result is a bare .ac3 elementary stream — the audio half of a disc-authoring project, not an everyday music file. Two things are worth knowing up front: most AVI files carry MP3 audio, so this is a lossy-to-lossy re-encode that cannot add back detail the original discarded; and if you simply want a playable sound file, AVI to MP3 is almost certainly the page you actually want.

AC-3 Format at a Glance

How to Convert AVI to AC3

1. Upload Your AVI File: Drag your .avi onto the page or click "Add Files". Queue several files to run with the same settings; the video is dropped from each and only the audio is written out.
2. Set the Bitrate: AC-3 is fixed as the output codec, so File Compression is where the decisions are. It opens on Quality Preset, which chooses a rate for you; switch to Constant Bitrate to pick an exact value from the dropdown, which runs from 32 kbps to 384 kbps, or to Custom Bitrate to type a value such as 448.
3. Set Audio Channel, Sample Rate and Trim (Optional): Audio Channel stays on ORIGINAL to keep the source layout, or forces STEREO or MONO. Audio Sample Rate should be set to 48000 Hz for anything disc-related. Trim takes a start time and a duration if you only need part of the soundtrack.
4. Convert and Download: Click Convert and save the .ac3. No sign-up, no watermark. Files upload over an encrypted connection, are processed on our servers, and are deleted automatically after a few hours.

The AC-3 Bitrate Table

AC-3 does not accept arbitrary bitrates. The standard defines a fixed ladder, and an encoder given anything else moves your request onto the nearest rung.

In our testing, asking the encoder for 200 kbps produced a 192 kbps stream and asking for 623 kbps produced 640 kbps — it snaps to the nearest allowed value rather than failing. So a typed Custom Bitrate is a request, not a guarantee, and it is worth checking the result if you have to hit an exact figure on a delivery sheet.

Where a Bare .ac3 File Fits

A .ac3 is an authoring and delivery intermediate. It is what DVD tools such as DVDStyler, DVDAuthor and tsMuxeR expect to mux alongside a video elementary stream when they build a disc, and it is what an AV receiver will decode over HDMI or S/PDIF when you want to test a surround setup with a known-good bitstream. It plays in VLC, foobar2000 and Kodi, so it is not unplayable — it simply has nowhere to store a track title, artwork or chapter marks, because there is no container around it. If you are building a DVD, pair the audio from this page with the video half from AVI to M2V. If you want a file to actually listen to, use AVI to MP3, and if you need a lossless master for editing, AVI to WAV writes uncompressed PCM.

Frequently Asked Questions

Does this keep the video from my AVI?

No. This is an audio-extraction conversion: the video track is discarded and only the soundtrack is written, as a raw AC-3 elementary stream. If you are authoring a disc and need both halves, take the audio here and the video from AVI to M2V, then mux them together in your authoring tool. If you wanted to keep a watchable video, convert the AVI to a video format instead.

Can a stereo AVI become real 5.1 surround?

No. AC-3 can carry up to 5.1 channels, but it cannot invent information that was never recorded. A two-channel AVI encodes as a 2.0 AC-3 track; forcing more channels would only add silent ones rather than produce discrete rears and an LFE. Genuine 5.1 output requires a source that already holds six discrete channels — check the source in VLC under Tools then Codec Information before expecting one.

Why is there no "specific file size" control on this page?

Because AC-3 is a constant-bitrate codec with a fixed ladder of allowed rates, so size follows directly from bitrate times duration and a size target would just be a bitrate in disguise. The control is deliberately hidden for AC-3 output. Work out what you need instead: 192 kbps is roughly 1.4 MB per minute, and 448 kbps is roughly 3.4 MB per minute.

What sample rate should I use, and what happens if I pick 8000 Hz?

Use 48000 Hz for anything disc- or broadcast-related, because that is what the DVD-Video and ATSC specifications call for. AC-3 itself supports only 32 kHz, 44.1 kHz and 48 kHz, so if you choose one of the lower rates in the dropdown — 8000, 12000, 16000 or 24000 Hz — the conversion snaps it up to the nearest supported rate rather than producing an out-of-spec file.

Will converting AVI to AC3 reduce the audio quality?

Slightly, in most cases. The soundtrack inside an AVI is usually MP3, which is already lossy, and AC-3 is lossy too, so you are stacking a second encode. Matching or exceeding the source bitrate — 192 kbps is a safe stereo choice — keeps the additional loss hard to hear. The exception is an AVI whose audio is PCM, which gives you a single clean encode from a lossless source.

My DVD authoring software rejected the file — what now?

Check three things in this order. The sample rate must be 48000 Hz, not "original", if the source was 44.1 kHz. The bitrate must be on the standard ladder and no higher than 448 kbps, since that is the DVD-Video ceiling for AC-3. And the channel count must be one the tool supports, usually 2.0 or 5.1 rather than something unusual. Re-running with 48000 Hz and 192 kbps clears the great majority of these rejections.

Can I get the original AC-3 track out of the AVI without re-encoding?

Not through this converter. A small number of AVI files do carry an AC-3 stream already, and that stream can in principle be demultiplexed byte-for-byte with a desktop tool such as VirtualDubMod. Our server always decodes and re-encodes the audio rather than copying the stream through, so if byte-identical preservation is the requirement, do the demux locally instead.

How are my files handled after conversion?

Your AVI is uploaded over an encrypted connection, the audio is extracted and encoded on our servers, and both the upload and the finished .ac3 are deleted automatically after a few hours. There is no sign-up, no watermark, and files are never shared or made public.