Extract Audio from M2TS to AC3 — Free Online Tool
Extract Dolby Digital AC3 audio from M2TS Blu-ray and AVCHD files directly in your browser. This tool strips the video stream entirely and re-encodes the audio to AC3 format — ideal for creating surround sound audio files compatible with DVD authoring, home theater systems, and broadcast workflows.
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FFmpeg Command
Copy this command to run the same conversion locally with FFmpeg on your desktop. Download FFmpeg
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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
M2TS files are MPEG-2 Transport Stream containers typically carrying high-definition video (H.264 or H.265) alongside audio tracks that may be encoded as DTS-HD, Dolby TrueHD, LPCM, or AAC. This conversion discards the video stream entirely and re-encodes whichever audio track FFmpeg selects by default into AC3 (Dolby Digital), a lossy format using perceptual audio coding at a default bitrate of 192k. Because the source audio codec in M2TS is rarely already AC3 at the target bitrate, a full decode-and-reencode pass is performed — not a stream copy. The output is a raw AC3 bitstream file, not wrapped in a container like MKV or MP4, making it directly usable for DVD/Blu-ray authoring tools and A/V receivers.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg binary. In the browser-based tool, this runs via FFmpeg.wasm compiled to WebAssembly — no installation required and no files leave your device. |
-i input.m2ts
|
Specifies the input M2TS file — a Blu-ray BDAV or AVCHD container that typically carries HD video alongside multi-channel audio streams such as Dolby TrueHD, DTS-HD, or LPCM. |
-vn
|
Disables video output entirely, telling FFmpeg to ignore all video streams in the M2TS file. This is what makes this an audio extraction tool rather than a full conversion — the H.264 or H.265 video data is discarded, keeping the output file small and audio-only. |
-c:a ac3
|
Encodes the audio using FFmpeg's native AC3 encoder, producing Dolby Digital output. Since M2TS source audio is typically TrueHD, DTS-HD, or LPCM, this performs a full decode-and-reencode rather than a stream copy. |
-b:a 192k
|
Sets the AC3 audio bitrate to 192 kilobits per second. This is a reasonable default for stereo content, though for 5.1 surround sound extracted from Blu-ray M2TS sources, 384k or 448k is recommended to better preserve surround field detail. |
output.ac3
|
Writes the result as a raw AC3 elementary stream file — not wrapped in a container like MKV or MP4. This format is directly compatible with Blu-ray and DVD authoring tools and hardware A/V receivers that accept Dolby Digital over S/PDIF. |
Common Use Cases
- Extracting a Dolby Digital 5.1 surround sound track from a Blu-ray rip for use in a DVD authoring project, where AC3 is the required audio format
- Converting AVCHD camcorder footage (.m2ts) to an AC3 audio track for import into professional video editing software that requires a discrete Dolby Digital audio file
- Creating a standalone AC3 audio file from a Blu-ray concert recording to play back through a home theater receiver that decodes Dolby Digital over S/PDIF optical
- Preparing broadcast-compliant audio from M2TS source material where downstream systems require AC3-encoded Dolby Digital rather than LPCM or AAC
- Archiving just the audio commentary or secondary audio track from a Blu-ray M2TS file as a compact Dolby Digital file without carrying along gigabytes of video data
- Demuxing audio from an AVCHD clip recorded on a Sony or Panasonic camcorder to produce an AC3 file for syncing with externally recorded video in post-production
Frequently Asked Questions
It depends on the source audio track in the M2TS file. If the original audio is already multi-channel (e.g., 5.1 DTS-HD or Dolby TrueHD), FFmpeg will decode it and re-encode the channels into AC3 5.1, preserving the surround layout. However, if the M2TS contains only stereo AAC or LPCM, the output AC3 will also be stereo. You can explicitly force 5.1 output by adding '-ac 6' to the FFmpeg command if your source material supports it.
Yes, this is a lossy conversion. Even if the original M2TS contains lossless audio like Dolby TrueHD or LPCM, re-encoding to AC3 introduces perceptual compression artifacts, especially at lower bitrates. The default 192k bitrate is a reasonable middle ground for 5.1 content, but for archival or professional use, consider raising it to 384k or 640k using the '-b:a' flag. Repeatedly re-encoding lossy-to-lossy (e.g., if the source was already AAC) will degrade quality further with each generation.
By default, FFmpeg selects the first audio stream in the M2TS file, which is typically the primary language track. M2TS containers from Blu-ray discs frequently carry multiple audio streams (e.g., DTS-HD main audio plus a Dolby Digital compatibility track, or multiple language dubs). To extract a specific track, add '-map 0:a:1' to the command (replacing '1' with the zero-indexed stream number you want). You can identify available streams by running 'ffmpeg -i input.m2ts' and reading the stream list.
Replace '192k' in the '-b:a 192k' flag with your desired bitrate. AC3 supports bitrates from 96k up to 640k — for standard stereo content, 192k is fine, but for 5.1 surround sound, 384k or 448k is generally recommended to avoid audible artifacts. The full command would look like: 'ffmpeg -i input.m2ts -vn -c:a ac3 -b:a 384k output.ac3'. Note that AC3 has a maximum bitrate of 640k, and exceeding standard Blu-ray spec values may cause compatibility issues with some hardware decoders.
Yes. On Linux or macOS, you can use a shell loop: 'for f in *.m2ts; do ffmpeg -i "$f" -vn -c:a ac3 -b:a 192k "${f%.m2ts}.ac3"; done'. On Windows Command Prompt, use: 'for %f in (*.m2ts) do ffmpeg -i "%f" -vn -c:a ac3 -b:a 192k "%~nf.ac3"'. The browser-based tool processes one file at a time, so the FFmpeg command is especially useful for batch jobs or files over 1GB.
This tool is specifically designed to extract audio only, so the output is a raw AC3 elementary stream rather than a multiplexed container. A raw .ac3 file is directly usable in DVD/Blu-ray authoring tools like DVDStyler or BDSup2Sub, and most A/V receivers and media players can decode it natively. If you need the AC3 audio muxed inside a video container alongside video, you would use a different workflow where you keep the video stream and specify the audio codec as AC3.
Technical Notes
M2TS uses the MPEG-2 Transport Stream structure with a 192-byte packet size (4-byte timestamp prepended to each 188-byte TS packet), which FFmpeg handles transparently during demuxing. The audio in M2TS Blu-ray sources is most commonly Dolby TrueHD, DTS-HD Master Audio, or uncompressed LPCM — all of which require a full decode step before re-encoding to AC3, unlike a simple stream copy. The AC3 codec in FFmpeg (libavcodec's native ac3 encoder) supports up to 5.1 channels and bitrates between 96k and 640k; it does not support 7.1 or Atmos object-based audio, so any M2TS source with more than 6 channels will be downmixed. Metadata such as track titles, language tags, and chapter markers from the M2TS source are not preserved in the raw AC3 output file, as the AC3 elementary stream format has no container-level metadata structure. If your M2TS file uses AC3 audio already at a compatible bitrate, you could alternatively use '-c:a copy' for a lossless stream copy instead of re-encoding, though this requires the source bitrate to exactly match a valid AC3 bitrate.