Convert MTS to AU — Free Online Tool
Convert MTS camcorder video files to AU audio format, extracting the H.264/AC-3 video's audio track and encoding it as uncompressed 16-bit big-endian PCM — the native encoding used in Sun's AU format. Useful for archiving camcorder audio on Unix systems or feeding raw audio data into legacy audio tools that require AU files.
to
FFmpeg Command
Copy this command to run the same conversion locally with FFmpeg on your desktop. Download FFmpeg
Drop your MTS 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
MTS files are AVCHD containers from Sony and Panasonic camcorders, wrapping an H.264 video stream alongside AC-3 or AAC audio in an MPEG-2 Transport Stream. During this conversion, FFmpeg discards the video stream entirely and decodes the compressed audio (AC-3 or AAC) from the MTS container, then re-encodes it as uncompressed PCM signed 16-bit big-endian audio, writing it into the AU container format developed by Sun Microsystems. The AU format has a minimal fixed header structure with no support for chapters, subtitles, or multiple audio tracks, so only the first audio track from the MTS file is preserved. The result is a raw, uncompressed audio file with no lossy audio encoding stage — the only quality impact comes from decoding the original compressed AC-3 or AAC source.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg application, the open-source multimedia processing engine running here via WebAssembly in your browser. On the command line, this is the binary that performs all decoding, filtering, and encoding work. |
-i input.mts
|
Specifies the input file — an MTS file in the AVCHD format, the MPEG-2 Transport Stream container used by Sony and Panasonic camcorders carrying H.264 video and AC-3 or AAC audio. FFmpeg probes this file to detect all streams and their codecs before processing begins. |
-c:a pcm_s16be
|
Sets the audio codec for the output to PCM signed 16-bit big-endian, which is the standard uncompressed encoding for Sun AU files. FFmpeg first decodes the compressed AC-3 or AAC audio from the MTS container, then re-encodes those raw samples as big-endian 16-bit integers — matching the byte order expected by the AU format's Sun/SPARC origins. |
output.au
|
Defines the output filename with the .au extension, which tells FFmpeg to write the result in the Sun AU container format. The video stream from the MTS file is automatically excluded because AU supports audio data only, and the minimal AU header is written with the sample rate and channel count inherited from the decoded MTS audio stream. |
Common Use Cases
- Extracting uncompressed audio from Sony or Panasonic camcorder footage for use with legacy Unix audio processing tools that require AU format input
- Archiving the audio track from AVCHD recordings as lossless PCM in an AU file for use in older Sun Solaris or Unix workstation environments
- Feeding camcorder interview audio into early digital audio workstation software or telephony systems that accept AU files as input
- Stripping the audio from an MTS recording into a simple, header-light AU file for analysis with low-level audio research or signal processing scripts
- Creating AU-format audio assets from camcorder footage for use in Java applications, which have historically used AU as a natively supported audio format via the javax.sound API
- Converting field-recorded MTS audio to AU format for ingestion into broadcast or Unix-based media archiving systems that predate modern container support
Frequently Asked Questions
There is one lossy step in this process: decoding the original compressed audio from the MTS file. If the camcorder recorded AC-3 or AAC audio (as most AVCHD devices do), FFmpeg fully decodes that compressed audio to raw PCM before writing it into the AU file. The AU output itself uses uncompressed PCM, so no additional lossy encoding is applied. The final AU file is as close to the original captured audio as the source codec allows, but it will not be bit-for-bit identical to what the camcorder's microphone recorded before AC-3 or AAC compression was applied.
AU is a purely audio-only format developed by Sun Microsystems with no provision for storing video data, chapters, or subtitles — it holds nothing but a simple header and raw audio samples. FFmpeg automatically omits the H.264 video stream from the MTS file when writing to AU because the container simply cannot hold it. If you need to preserve the video, you should convert to a format like MP4 or MKV instead.
The AU format supports only a single audio track, so FFmpeg will default to mapping only the first audio stream from the MTS file. Any secondary audio tracks — such as a second microphone channel recorded by some AVCHD camcorders — will be silently dropped. If you need a specific non-default audio track, you can add a '-map 0:a:1' flag to the FFmpeg command to select the second audio stream before the output filename.
The AU format supports several PCM encodings beyond the default pcm_s16be, including pcm_mulaw, pcm_alaw, pcm_s8, and pcm_u8. To switch, replace '-c:a pcm_s16be' with your preferred codec, for example: 'ffmpeg -i input.mts -c:a pcm_mulaw output.au'. The mu-law and A-law encodings are commonly used in telephony contexts and will produce smaller files at the cost of a narrower dynamic range compared to 16-bit linear PCM.
Yes. On Linux or macOS, you can loop over all MTS files in a directory with: 'for f in *.mts; do ffmpeg -i "$f" -c:a pcm_s16be "${f%.mts}.au"; done'. On Windows PowerShell, use: 'Get-ChildItem *.mts | ForEach-Object { ffmpeg -i $_.FullName -c:a pcm_s16be ($_.BaseName + ".au") }'. This is especially practical for AU conversions since the format is simple and FFmpeg processes each file quickly without complex encoding overhead.
Significantly larger in most cases. MTS files store audio as compressed AC-3 or AAC, typically at 128–256 kbps. The AU output uses uncompressed PCM at 16-bit stereo, which at 44.1 kHz runs roughly 1,411 kbps — five to ten times larger per second of audio. A 10-minute MTS camcorder clip might have an audio track of around 15–30 MB compressed, which could expand to 100 MB or more as uncompressed AU. The video stream is dropped, so the AU file will still be much smaller than the original MTS file overall.
Technical Notes
The AU format's structure is intentionally minimal: a 24-byte fixed header containing a magic number, data offset, data size, encoding type, sample rate, and channel count, followed immediately by raw audio samples. Because AU lacks extensible metadata fields, none of the MTS file's embedded camcorder metadata — recording date, GPS coordinates, camera model, or timecode — is carried into the output file. The default encoding used here is pcm_s16be (signed 16-bit big-endian PCM), which reflects AU's Sun Microsystems heritage on big-endian SPARC architectures; this byte order may require byte-swapping if consumed by little-endian x86 tools expecting pcm_s16le. The AU format's sample rate and channel count fields are preserved correctly by FFmpeg from the decoded source audio. AU files produced this way are fully readable by Java's javax.sound.sampled API without additional libraries, which is a practical advantage for JVM-based applications. There is no container-level seeking index in AU, meaning very large AU files converted from long MTS recordings may seek slowly in some players.