Convert MPEG to AC3 — Free Online Tool
Convert MPEG video files to AC3 (Dolby Digital) audio by extracting and re-encoding the MP2 or AAC audio track into the AC3 format. This is ideal for preparing broadcast-ready Dolby Digital audio from legacy MPEG sources used in DVD authoring and home theater systems.
to
FFmpeg Command
Copy this command to run the same conversion locally with FFmpeg on your desktop. Download FFmpeg
Drop your MPEG file here
or click to browse
Free — no uploads, no signups. Your files never leave your browser.
Settings
Note: Browser-based encoding uses approximate quality targets. For precise CRF compression, copy the FFmpeg command above and run it on your desktop.
Estimated output:
Conversion Complete!
DownloadHow It Works
MPEG files typically carry MP2 (MPEG Layer 2) or occasionally AAC audio streams encoded alongside MPEG-1 or MPEG-2 video. This conversion strips the video entirely and re-encodes only the audio stream from MP2/AAC into AC3 using Dolby Digital compression. Because MP2 and AC3 are both lossy formats with different psychoacoustic models and bitrate structures, the audio undergoes a full decode-then-reencode transcode — not a simple remux — which means the audio is decompressed from MP2 and recompressed into AC3 at the specified bitrate (default 192k). The video stream is discarded since AC3 is a pure audio container.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg tool. In this browser-based tool, FFmpeg runs locally via WebAssembly (FFmpeg.wasm) — no data is sent to a server. The same command can be run on your desktop for files over 1GB. |
-i input.mpeg
|
Specifies the input MPEG file, which may contain MPEG-1 or MPEG-2 video alongside an MP2, MP3, or AAC audio track. FFmpeg will demux all streams and make them available for processing. |
-c:a ac3
|
Selects the AC3 (Dolby Digital) encoder for the audio stream, transcoding the source MP2 or other MPEG audio into Dolby Digital format. No video codec is specified because the output container (.ac3) is audio-only and the video stream is automatically dropped. |
-b:a 192k
|
Sets the AC3 audio bitrate to 192 kilobits per second, which is a standard bitrate for stereo Dolby Digital tracks in DVD and broadcast applications. Increase to 320k–448k for higher fidelity or for multichannel audio. |
output.ac3
|
Defines the output file as a raw AC3 bitstream file with the .ac3 extension. This format is a bare Dolby Digital audio container compatible with DVD authoring tools, AV receivers, and broadcast multiplexers. |
Common Use Cases
- Extracting Dolby Digital-compatible audio from legacy broadcast MPEG recordings for use in DVD authoring software that requires AC3 tracks
- Converting MPEG capture card recordings into AC3 for import into a home theater system or AV receiver that supports Dolby Digital passthrough
- Preparing audio from MPEG-2 television recordings for use in video editing timelines that require discrete AC3 audio tracks
- Archiving the audio portion of MPEG news or broadcast footage into a standard Dolby Digital format for long-term storage and compatibility
- Supplying AC3 audio files to multiplexers when re-authoring a DVD from raw MPEG-2 sources where the original MP2 track is not accepted
- Converting MPEG audio to AC3 for compatibility with Blu-ray authoring tools that mandate Dolby Digital encoded audio streams
Frequently Asked Questions
Yes, some quality loss is inevitable. MP2 audio in MPEG files is already a lossy format, and transcoding to AC3 means the audio is decoded from MP2 and then recompressed using Dolby Digital's encoder. This generation loss is most noticeable at lower bitrates. Using a higher AC3 bitrate such as 320k or 384k helps minimize the degradation compared to the default 192k.
AC3 is a pure audio container format — it cannot hold video streams. The conversion intentionally discards the MPEG-1 or MPEG-2 video track and extracts only the audio. If you need to keep the video alongside Dolby Digital audio, you should mux the AC3 output into a container like MKV or MP4 rather than outputting a standalone .ac3 file.
DVD-Video specifications allow AC3 audio bitrates between 96k and 448k, with 192k and 224k being the most common for stereo tracks. If the source MPEG file has a stereo MP2 track at 192k, matching or slightly exceeding that at 192k–256k in AC3 is a reasonable choice. For 5.1 surround mixes, 384k or 448k is standard. Note that a stereo MP2 source cannot be upconverted to true 5.1 surround — the channel count of the source limits the output.
Replace the value after -b:a in the command with your desired bitrate. For example, to encode at 384k, the command becomes: ffmpeg -i input.mpeg -c:a ac3 -b:a 384k output.ac3. AC3 supports bitrates from 96k up to 640k, but for stereo content the practical range is 128k to 320k, and for 5.1 content 384k to 448k is typical for broadcast and DVD use.
Yes. On Linux or macOS you can use a shell loop: for f in *.mpeg; do ffmpeg -i "$f" -c:a ac3 -b:a 192k "${f%.mpeg}.ac3"; done. On Windows Command Prompt: for %f in (*.mpeg) do ffmpeg -i "%f" -c:a ac3 -b:a 192k "%~nf.ac3". This processes every MPEG file in the current directory and outputs a corresponding .ac3 file with the same base name.
Yes, it does. MPEG files can contain MP2, MP3 (libmp3lame), or AAC audio. MP2 is the most common in broadcast MPEG-2 recordings and has a different frequency response than AAC, which is typically found in newer MPEG files. All of these are decoded to raw PCM before being re-encoded as AC3, so the quality of the AC3 output is bounded by the fidelity of the source — a low-bitrate MP2 track at 128k will produce a lower-quality AC3 than a 256k AAC source regardless of the target AC3 bitrate.
Technical Notes
AC3 (Dolby Digital) uses a transform-based psychoacoustic compression model that is fundamentally different from the subband coding used in MP2, which is the default audio codec in MPEG-2 broadcast files. Transcoding between these two lossy formats always involves a full decode-encode cycle with attendant quality loss. The AC3 encoder in FFmpeg (the native ac3 codec) is well-tested and produces standards-compliant output suitable for DVD and broadcast use. AC3 supports up to 5.1 channels, but if the MPEG source only contains a stereo or mono MP2 track, the output AC3 will also be stereo or mono — no upmixing occurs by default. Metadata such as program information or timecodes embedded in the MPEG container is not carried over to the .ac3 output file since the AC3 format has no equivalent metadata container. If you need chapter markers or stream metadata preserved, consider muxing the resulting AC3 into an MKV or MP4 container instead of using a bare .ac3 file. The maximum AC3 bitrate of 640k is rarely used in practice; DVD-Video caps AC3 at 448k, and most Blu-ray authoring uses 640k only for 7.1 configurations.