Extract Audio from M2TS to AU — Free Online Tool
Extract audio from M2TS Blu-ray and AVCHD files and save it as a Sun AU file with uncompressed PCM audio. This tool demuxes the audio stream from the M2TS transport stream container and re-encodes it to 16-bit big-endian PCM (pcm_s16be), producing a lossless, headerless AU file compatible with Unix audio tools.
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FFmpeg Command
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Estimated output:
Conversion Complete!
DownloadHow It Works
M2TS files are MPEG-2 Transport Stream containers typically carrying multiplexed video (H.264 or H.265), audio (AAC, AC-3, DTS, or TrueHD), and subtitle streams. During this conversion, FFmpeg demuxes the M2TS transport stream, discards the video entirely using the -vn flag, and transcodes the first audio stream to 16-bit big-endian signed PCM — the default and most compatible codec for the AU format. The AU container itself is extremely minimal: it stores a small fixed header describing sample rate, channel count, and encoding type, followed by raw PCM sample data. If the source M2TS audio is compressed (e.g., AAC or AC-3), it will be fully decoded to uncompressed PCM during this process, which guarantees lossless output quality but results in larger file sizes than the source audio track.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg binary — the underlying engine that performs all demuxing, decoding, and encoding. On this page it runs via FFmpeg.wasm compiled to WebAssembly and executed entirely in your browser. |
-i input.m2ts
|
Specifies the input file — an M2TS MPEG-2 Transport Stream container as used on Blu-ray discs and AVCHD camcorders. FFmpeg will parse the transport stream to locate and demux all multiplexed video, audio, and subtitle streams. |
-vn
|
Disables video output entirely, instructing FFmpeg to skip video stream decoding and produce an audio-only output. This is essential here because AU is a pure audio format and also avoids wasting CPU cycles decoding potentially complex H.264 or H.265 Blu-ray video. |
-c:a pcm_s16be
|
Sets the audio codec to 16-bit signed big-endian PCM, which is the native and default encoding for Sun AU files. This decodes whatever compressed audio codec is in the M2TS source (such as AAC or AC-3) into raw uncompressed PCM samples stored in big-endian byte order. |
output.au
|
Specifies the output filename. The .au extension tells FFmpeg to use the Sun AU container format. The resulting file will contain only the PCM audio stream with a minimal AU header, compatible with Unix audio tools and legacy systems that support this format. |
Common Use Cases
- Feeding Blu-ray rip audio into legacy Unix audio processing pipelines or command-line tools that natively consume AU files
- Extracting raw uncompressed audio from AVCHD camcorder footage for use in scientific or broadcast signal analysis software that requires PCM AU input
- Archiving the audio track from a Blu-ray M2TS file in a simple, format-agnostic PCM container with no lossy compression steps
- Preparing audio from M2TS home video captures for use with older Sun Solaris or Unix workstation audio applications that predate modern format support
- Stripping and converting the audio from a Blu-ray presentation or concert recording for playback testing on Unix-based embedded or legacy media systems
- Generating a raw PCM AU reference file from M2TS source audio to use as a ground-truth comparison when evaluating compressed audio codec quality
Frequently Asked Questions
If the audio track inside your M2TS file is already uncompressed PCM, then no quality is lost — the samples are decoded and written directly to AU. If the source audio is a compressed codec like AAC, AC-3, or DTS (common on Blu-ray M2TS files), the decompression step introduces the same minor artifacts inherent in that original encoding, but the final AU file is then stored as uncompressed PCM with no additional lossy step. The AU output itself is always lossless 16-bit PCM regardless of the source codec.
M2TS files frequently contain multiple audio tracks — for example, a primary Dolby TrueHD track and a secondary AAC commentary track. By default, FFmpeg selects only the first (or highest-priority) audio stream for extraction. If you need a specific track, you can modify the command by adding a stream selector like -map 0:a:1 to target the second audio track. The resulting AU file can only hold a single audio stream, so multi-track selection is not possible in a single AU output.
Blu-ray M2TS files store audio in compressed formats like AAC, AC-3, or TrueHD, which achieve significant file size reductions compared to raw PCM. The AU format stores audio as uncompressed 16-bit big-endian PCM, so the output reflects the true uncompressed size of the audio data — typically 5 to 10 times larger than a compressed AAC or AC-3 source at CD quality sample rates. For example, one hour of stereo audio at 48kHz in 16-bit PCM occupies roughly 691 MB.
Yes, AU files can technically store multi-channel PCM audio — the format header supports arbitrary channel counts. If your M2TS contains a 5.1 or 7.1 surround audio track, FFmpeg will decode it to multi-channel 16-bit big-endian PCM and write all channels to the AU file. However, compatibility of multi-channel AU files varies widely across legacy Unix audio tools, many of which were designed for mono or stereo. If broad compatibility is important, consider downmixing to stereo by adding -ac 2 to the command.
The command as shown preserves the original sample rate from the M2TS source, which for Blu-ray content is typically 48000 Hz. To resample to a different rate — for example, 44100 Hz for CD compatibility — add the flag -ar 44100 before the output filename: ffmpeg -i input.m2ts -vn -c:a pcm_s16be -ar 44100 output.au. You can also switch to 8-bit encoding by replacing pcm_s16be with pcm_s8 or pcm_u8 if your target Unix audio tool requires it, though this reduces dynamic range significantly.
No. The Sun AU format has an extremely minimal header that contains only the data offset, data size, encoding type, sample rate, and channel count. It has no standardized support for metadata fields like track title, language, artist, or album. Any such tags present in the M2TS stream are discarded during conversion. If metadata preservation matters, consider extracting to a format like FLAC or WAV, which support rich metadata tagging.
Technical Notes
The Sun AU format was originally developed by Sun Microsystems for SunOS and became a common audio interchange format on Unix systems and early internet audio due to its simplicity. Its header is just 28 bytes (or larger if an annotation field is included), followed by raw sample data. The default codec for AU in FFmpeg is pcm_s16be — 16-bit signed, big-endian PCM — which reflects AU's Unix/SPARC heritage where big-endian byte order was standard. This is distinct from WAV, which uses little-endian PCM. M2TS sources from Blu-ray discs may contain audio encoded as Dolby TrueHD, DTS-HD Master Audio, AC-3, or AAC at sample rates of 48000 Hz or higher; all of these will be fully decoded before being written as PCM to AU. Because the AU format does not support chapters, subtitle streams, or secondary audio tracks, all of this information from the M2TS is silently dropped. The -vn flag ensures no video decoding occurs at all, which makes the conversion faster and avoids unnecessary CPU work on potentially large H.264 or H.265 Blu-ray video streams. There are no special FFmpeg flags required for AU output — FFmpeg infers the container and codec from the .au file extension.