MTS to AU Converter

Extract AU Audio from MTS: What This Tutorial Covers

This converter pulls the audio track out of an MTS (AVCHD) camcorder clip and saves just the sound as an AU (.au / .snd) file — the H.264 video is discarded and you keep only the soundtrack. AU is Sun Microsystems' minimal late-1980s Unix sound format, so this is a deliberately narrow target: it makes sense when a legacy Unix tool, an older Java application, or a scientific or instrumentation system specifically wants an .au feed. This walk-through shows where the .MTS clip hides on the memory card, what happens to the audio depending on how your camera recorded it, why the AU comes out large, the one real gotcha — a slight length drift from AC-3's decode padding — and, importantly, when you should pick MTS to WAV or MTS to MP3 instead.

How to Convert MTS to AU

1. Upload Your MTS File: Drag and drop your .MTS (or .M2TS) clip onto the page, or click "+ Add Files" to browse. Queue several clips to extract them in one batch with the same settings.
2. Set Audio Channel (Optional): Audio Channel sits on Original, which copies the source layout into the .au. Set it to mono if a legacy reader expects single-channel audio, or to stereo to fold a surround track down to two channels.
3. Set Audio Sample Rate or Trim (Optional): Audio Sample Rate also defaults to Original; classic AU pipelines often expect 8000 Hz, so set it there only if the consuming tool requires it. Use Trim to keep only part of a long recording.
4. Convert and Download: Click "Convert" and save your .au file individually or as a ZIP. No sign-up, no watermark.

Walk-through: Finding the Right File, and What Happens to the Audio

MTS is the AVCHD camcorder format — the codec system Sony and Panasonic introduced in 2006 — and on the card it is a folder structure, not a single file. Footage lives under PRIVATE/AVCHD/BDMV/STREAM/, where each recording is a .MTS clip (the extension becomes .M2TS once the clip is copied to a computer; the bytes are the same MPEG-2 Transport Stream). This tool takes the individual stream file, so browse into that STREAM/ directory and upload the actual .MTS clip rather than the top-level AVCHD folder.

This converter writes 16-bit big-endian linear PCM into the .au — the standard uncompressed encoding for the format, stored in the fixed 24-byte .snd header Sun defined. It does not default to AU's historical 8-bit µ-law telephone encoding, so there is no additional telephone-grade quality cut layered on top of whatever the source already was. What the sound starts from depends entirely on how your camcorder recorded it, and the two AVCHD audio types behave very differently here:

• Dolby AC-3 (Dolby Digital) source — the common case. Most consumer AVCHD camcorders record AC-3, which is already a lossy format (up to 5.1 channels). Decoding it to uncompressed PCM inside the AU adds no new generation of loss — but it also cannot rebuild detail the AC-3 encode already discarded. You get a clean copy of exactly the quality the source had, not an upgrade.
• Linear PCM source — some professional models. A few pro camcorders record uncompressed Linear PCM. Because that source is already lossless, writing it into a PCM AU is a genuinely lossless handoff — camcorder PCM straight to PCM-in-AU, with no transcode in between. Keep Audio Sample Rate on Original so the AU inherits the source rate and depth.

Either way, the AU is uncompressed, so expect it to be much larger than the clip's audio bitrate suggests — roughly 10 MB per minute for 16-bit/44.1 kHz stereo PCM. That size is the cost of an uncompressed, legacy-friendly file:

• Feeding a Unix tool, Java application, or scientific pipeline that needs .au? Keep the defaults — plain 16-bit big-endian PCM in a .snd header is exactly what those readers expect.
• A classic AU pipeline that wants telephone-style audio? Drop Audio Sample Rate to 8000 Hz and Audio Channel to mono to match the format's 8 kHz heritage, accepting the smaller, lower-fidelity result.
• Do not expect a setting that recovers fidelity. There is no "higher quality" option that rebuilds what AC-3 compressed away; a higher sample rate only makes the file larger.

Common Errors and How to Fix Them

• "I can't find a file to upload — just folders" — You are looking at the card's PRIVATE/AVCHD/BDMV/ tree. Browse down into STREAM/ and pick the individual .MTS (or .M2TS) clip; that is the file this tool needs.
• "The AU won't play on my phone or in my browser" — Expected. AU never became a consumer format; smartphones, browsers, and most media apps do not read it. AU is a feed for the specific legacy or scientific tool that asked for it — for everyday playback, extract to MTS to MP3 instead.
• "The AU is huge compared to the clip's audio" — Also expected. PCM is uncompressed, so even a modestly-bitrated AC-3 track becomes about 10 MB per minute as 16-bit stereo PCM. If size matters more than legacy compatibility, MTS to MP3 is far smaller.
• "The audio sounds no better than the original" — Expected when the source is AC-3. Decoding AC-3 to PCM gives a faithful copy, not added fidelity; only an LPCM source is a truly lossless handoff.
• "The extracted audio is slightly longer than the video / drifts out of sync" — AC-3 (like all lossy audio) carries a few milliseconds of encoder padding, typically around 10–20 ms, and some editors read the camcorder's muxing delay differently. On a single clip this is usually inaudible, but in a tight edit you may need to nudge the track into alignment.
• "My clip has 5.1 surround but I only got stereo" — AVCHD AC-3 can carry up to 5.1 channels; this tool's Audio Channel control offers Original, mono, and stereo, so a surround source is most reliably handled as a stereo fold-down.

When This Doesn't Work — and the Simpler Routes

AU makes sense for one narrow case: a legacy Unix tool, an older Java application (the classic AudioClip era expected audio/basic), or a scientific or instrumentation system built around the format's trivially simple 24-byte header. If that is not your situation, AU is the wrong target. For editing, a plain WAV carries the same uncompressed 16-bit PCM but is accepted by virtually every audio editor on every platform, so MTS to WAV is the standard editing route; MTS to MP3 is the right pick if you only need the soundtrack to play on a phone, car stereo, or generic player. The conversion can also fail outright if the .MTS is partially corrupted — often from pulling the card before the camcorder finished writing — in which case the audio stream may be unreadable even when a player can still scrub the video; re-copy the clip from the card rather than fight a broken file. And if you would rather keep the picture as well as the sound, convert MTS to MP4 re-encodes both streams into one playable file.

Frequently Asked Questions

Does this keep the video, or just the audio?

Just the audio. This is an extraction: the H.264 video inside your MTS clip is discarded and only the soundtrack is written out as an AU file. If you want to keep the picture too, convert MTS to MP4 instead, which re-encodes both the video and audio into a single playable file.

Why would I convert MTS to AU instead of WAV or MP3?

Only when a downstream tool specifically wants an .au file. The realistic cases are narrow: legacy Unix sound tooling and shell pipelines, older Java applications that expected audio/basic, and scientific, embedded, or instrumentation systems built around AU's minimal 24-byte header. For everything else, MTS to WAV gives you the same uncompressed PCM in a format every editor reads, and MTS to MP3 gives you a small, broadly playable file. AU and WAV can hold the identical 16-bit PCM payload — WAV is just the one virtually everything accepts, so pick AU only when the .au extension itself is the requirement.

What encoding does this put inside the .au file?

16-bit big-endian linear PCM — the standard uncompressed encoding for the AU container, written into the fixed 24-byte .snd header (magic 0x2e736e64) that Sun Microsystems defined in the late 1980s. The whole format is big-endian, including the sample data. This converter does not default to AU's historical 8-bit µ-law telephone encoding, so you are not adding a second, telephone-grade quality reduction on top of whatever the camcorder recorded — you get a faithful uncompressed copy that a Unix tool, Java application, or scientific system can read.

Will the AU sound better than the audio already in my MTS clip?

It depends on how the camera recorded it, and the honest answer is usually no. Most consumer AVCHD camcorders record Dolby AC-3, which is already lossy — so decoding it to PCM inside an AU gives a faithful copy but cannot exceed the source. Some professional models record uncompressed Linear PCM, and that case is different: PCM straight into a PCM AU is a genuinely lossless handoff with no transcode at all. Either way you get a clean copy of the original; only the LPCM source starts from true lossless audio.

Why is my AU file so much larger than the original soundtrack?

Because this converter writes uncompressed PCM into the AU. AVCHD audio is compressed (AC-3 packs a stereo track into a few hundred kbps), whereas 16-bit/44.1 kHz stereo PCM runs about 10 MB per minute regardless of the source bitrate. In our testing, a 60-second AC-3 stereo MTS clip extracted to a roughly 10 MB 16-bit PCM .au. The size jump is the cost of an uncompressed, legacy-friendly format, not a setting you can tune away; for a small file, extract to MTS to MP3 instead, and to squeeze an AU back down later, AU to Opus is the reverse route.

How are my files handled, and how long are they kept?

Your MTS file is uploaded over an encrypted connection, processed on our servers, and deleted automatically a few hours after conversion — no sign-up, no watermark, never shared or made public. The main practical limit is upload size and time rather than the extraction itself: an MTS clip carries full HD video alongside the audio, so a long recording can take a while to upload even though pulling out the soundtrack is quick.