Convert M2TS to AC3 — Free Online Tool
Extract and convert the audio from an M2TS Blu-ray or AVCHD file into AC3 Dolby Digital format, producing a standalone .ac3 file encoded with the ac3 codec at 192k bitrate. This is ideal for isolating Dolby Digital surround sound audio from Blu-ray source material for use in compatible home theater systems, DVD authoring, or 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 is a MPEG-2 Transport Stream container that typically carries one or more audio tracks encoded in formats such as AAC, AC3, DTS, or TrueHD alongside high-definition video. During this conversion, FFmpeg reads the M2TS container, discards all video streams entirely, and re-encodes the primary audio stream using the ac3 encoder — Dolby Digital's codec — into a raw .ac3 bitstream file. If the source audio happens to already be AC3, it is still re-encoded rather than stream-copied, ensuring the output bitrate and channel configuration conform to your chosen settings. The result is a standalone AC3 audio file with no video wrapper, suitable for direct playback on Dolby Digital-capable devices or muxing into another container.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg application, which is running here as FFmpeg.wasm compiled to WebAssembly and executing entirely inside your browser — no data leaves your device. |
-i input.m2ts
|
Specifies the input M2TS file, a Blu-ray BDAV or AVCHD transport stream that may contain HD video, one or more audio tracks (AC3, AAC, TrueHD, etc.), and subtitle streams. |
-c:a ac3
|
Instructs FFmpeg to encode the audio stream using the ac3 codec, which produces Dolby Digital output. All video and subtitle streams are implicitly excluded because the .ac3 output format is audio-only. |
-b:a 192k
|
Sets the AC3 audio bitrate to 192 kilobits per second. This is a reasonable default for stereo Dolby Digital audio; for 5.1 surround content extracted from Blu-ray M2TS sources, increasing this to 384k or 640k is strongly recommended to preserve surround fidelity. |
output.ac3
|
Defines the output filename with the .ac3 extension, which tells FFmpeg to write a raw Dolby Digital Elementary Stream. This file can be played directly by most media players or muxed into a DVD VOB, MKV, or TS container. |
Common Use Cases
- Extracting the Dolby Digital 5.1 surround sound audio track from a Blu-ray rip in M2TS format to author onto a DVD, which requires AC3 audio
- Isolating a commentary or alternate audio track from an AVCHD camcorder recording stored as M2TS for use in a broadcast post-production pipeline
- Converting the audio portion of a Blu-ray concert rip to AC3 so it can be played back through a home theater AV receiver that only decodes Dolby Digital
- Preparing a standalone AC3 audio file from M2TS source material to mux into an MKV or MP4 container using a separate tool or workflow
- Archiving the audio track from an AVCHD M2TS clip as a discrete AC3 file for long-term storage alongside the raw video stream
- Creating a Dolby Digital audio file from a Blu-ray M2TS source to synchronize with an externally processed video track during film post-production
Frequently Asked Questions
Yes, some quality loss is expected because AC3 is a lossy codec. If your M2TS source already contains a lossy audio track (such as AAC or an existing AC3 stream), converting it to AC3 introduces a second generation of lossy compression, which can subtly degrade quality. If the source contains a lossless track like TrueHD or DTS-HD Master Audio, the conversion to AC3 at 192k will be a significant downgrade from lossless. For the best results with lossless source audio, consider using a higher bitrate like 384k or 640k in the FFmpeg command.
No. The .ac3 output format is a raw audio bitstream container that cannot hold video data. FFmpeg automatically omits all video streams when the output format is AC3, so only the audio is encoded and written to the file. If you need to keep the video alongside the AC3 audio, you would instead mux both streams into a container format such as MKV or TS.
By default, FFmpeg selects the first (or highest-priority) audio stream from the M2TS file and encodes it to AC3. If your M2TS contains multiple audio tracks — for example, a primary 5.1 mix and a director's commentary — only one will be converted. To extract a specific track, you can add a stream selector such as -map 0:a:1 to the FFmpeg command to target the second audio stream by index.
The bitrate is controlled by the -b:a flag in the command. The default is 192k, which is a common baseline for AC3 stereo audio, but AC3 supports bitrates up to 640k, which is recommended for 5.1 surround content. For example, to encode at 384k for a higher-quality 5.1 output, run: ffmpeg -i input.m2ts -c:a ac3 -b:a 384k output.ac3. AC3 5.1 content on Blu-ray is often authored at 640k, so using a higher bitrate better preserves surround fidelity.
Yes. On Linux or macOS, you can use a shell loop: for f in *.m2ts; do ffmpeg -i "$f" -c:a ac3 -b:a 192k "${f%.m2ts}.ac3"; done. On Windows Command Prompt, use: for %f in (*.m2ts) do ffmpeg -i "%f" -c:a ac3 -b:a 192k "%~nf.ac3". This is especially useful when extracting audio from a series of AVCHD clips or Blu-ray chapter files.
No. The AC3 format is a raw audio-only bitstream and has no capacity to carry subtitle data. All subtitle tracks present in the M2TS file are silently discarded during conversion. If you need to preserve subtitles, you would need to use a container format such as MKV or TS that supports both AC3 audio and subtitle streams.
Technical Notes
AC3, formally standardized as Dolby Digital, supports up to 5.1 discrete audio channels and bitrates between 32k and 640k. The ac3 encoder in FFmpeg is a native implementation that reliably handles stereo and multichannel input from M2TS sources. When the M2TS source contains a multichannel audio stream (e.g., 5.1 from a Blu-ray), FFmpeg will preserve the channel layout through to the AC3 output, provided the bitrate is set high enough — 384k is the practical minimum for 5.1, with 640k being the Blu-ray standard. Raw .ac3 files lack a container-level metadata layer, meaning track titles, language tags, and chapter markers from the M2TS are not carried over. The output is a raw Elementary Stream, which many media players (VLC, MPC-HC) play directly, but some devices may require the AC3 to be wrapped inside an MPEG-TS or VOB container to be recognized. If your M2TS source audio is already AC3, stream copying with -c:a copy would be lossless and faster, but this tool re-encodes to guarantee a clean output at the specified bitrate.