AVCHD to AU Converter

AVCHD to AU: A Sun Audio File Written in G.711 mu-law

.au is the Sun/NeXT audio format — one of the oldest sound containers still in circulation, identified by the four bytes .snd at the start of the file. It is not a general-purpose music format and never was. It exists today mainly because Unix and Java tooling grew up around it: javax.sound.sampled reads it natively, older telephony and voice-response systems accept it, and a long tail of scientific and academic software still lists it as an input.

This page takes an AVCHD camcorder recording — an MPEG-2 transport stream carrying H.264 video next to a Dolby Digital (AC-3) or linear-PCM soundtrack — throws the picture away, and writes the audio as 8-bit G.711 mu-law. There is no codec choice and no bitrate control; the whole configurable surface is the channel count, the sample rate and an optional trim. What follows is exactly what that produces and how to predict the size.

How to Convert AVCHD to AU

1. Upload Your AVCHD File: Drag the .avchd onto the page or click "+ Add Files". Only the .avchd extension is accepted here. Several files can be queued and all convert with the same settings.
2. Set Audio Channel: The dropdown offers ORIGINAL, MONO and STEREO, with nothing preselected, so ORIGINAL applies and an AVCHD's stereo soundtrack stays stereo. Choosing MONO halves the output size exactly, because mu-law spends one byte per sample per channel.
3. Set Audio Sample Rate: The dropdown offers ORIGINAL plus 8000, 12000, 16000, 24000, 44100 and 48000 HZ. This is the single biggest lever on file size, and unlike most codecs mu-law imposes no restriction of its own — every entry in that list is honoured literally. Trim takes a Start time and a Duration if you only need a section.
4. Convert and Download: Click Convert and save the .au. Files are uploaded over an encrypted connection, decoded and re-encoded on our servers, and deleted automatically after a few hours — no sign-up, no watermark, never shared or made public.

What the AU File Actually Contains

Every field below was read out of an .au produced from a 6-second AVCHD test file with a 48 kHz stereo AC-3 track.

That last row is worth being explicit about: the Audio Codec group renders on this page as a heading with nothing under it. Every codec entry carries an allow-list of output formats it may be offered for, and AU appears on none of them, so the group is empty and there is no default marked either. The conversion pipeline then falls back to the container's own default codec, which for .au is mu-law. The File Compression section is hidden for the same underlying reason — mu-law has one fixed rate, so a bitrate or quality control would have nothing to adjust.

Sizing the Output: One Multiplication

Because mu-law writes exactly one byte per sample per channel, the size is arithmetic rather than an estimate:

bytes = sample rate x channels x seconds + 32

The first row is the one to notice. Left alone, this conversion produces an AU file at 768 kbit/s — three times the bitrate of the AC-3 track it came from, and considerably larger than the audio inside the original AVCHD. That is not a fault; it is what an uncompressed-style format does. If size matters, drop the sample rate, choose MONO, or use a format that actually compresses: AVCHD to MP3 for general listening, or AVCHD to WAV if you want full 16-bit PCM rather than 8-bit companded samples.

Frequently Asked Questions

Is 8-bit mu-law really as bad as "8-bit" sounds?

Not as bad as linear 8-bit, but it is still a serious downgrade from a camcorder soundtrack. G.711 mu-law is companded: it applies a logarithmic curve before quantising, so the 256 available codes are packed tightly around quiet signals and spread out across loud ones. The result carries roughly the perceived dynamic range of 12 to 14 linear bits rather than 8 — which is why it was good enough for the entire world's telephone network. What it will not do is flatter music, ambience or anything with a wide quiet-to-loud span, and quantisation noise on sustained quiet passages is audible.

Can I get an A-law or 16-bit PCM .au from this page?

No. The conversion pipeline knows how to write all three encodings that the AU container commonly carries — mu-law, A-law and 16-bit big-endian PCM — but the option set hides every codec entry on AU output, so the Audio Codec heading appears with nothing under it and only the container default, mu-law, is reachable. If you need 16-bit linear samples, AVCHD to WAV gives you PCM in a container that every tool reads, and most software that accepts .au will accept a WAV too.

Why is my AU file bigger than the AVCHD's audio track?

Because mu-law does not compress the way a perceptual codec does. AVCHD stores its soundtrack as Dolby Digital, typically somewhere between 192 and 640 kbit/s for a stereo mix, using a psychoacoustic model to discard what you would not hear. Mu-law simply writes one byte per sample per channel, so at the source's own 48 kHz stereo it lands at a flat 768 kbit/s no matter what the content is. Halving the sample rate halves the file; choosing MONO halves it again.

What happens if the AVCHD has no audio track?

The job fails and no file is written. We ran that case deliberately: feeding a video-only .avchd to this converter produces "Output file does not contain any stream" and nothing lands in your downloads. It is the right outcome for an audio-only target, but it does mean an unexplained failure here usually means the source is silent rather than that something is broken. Check the file in a player first.

My camcorder wrote .MTS files. Is this the right page?

Only if your file is literally named .avchd, which this page accepts exclusively. No camera writes that extension — AVCHD recordings are .MTS on the memory card and .M2TS after being imported into a BDMV folder or onto a disc — so a .avchd is nearly always the work of a converter or a manual rename. The transport-stream bytes are the same, so renaming works either way, but MTS to AU and M2TS to AU exist so you do not have to.

Does the AU file keep the recording date or any camcorder metadata?

No. The AU header has room for a variable-length annotation field and nothing else — there is no tag structure comparable to ID3 or the metadata atoms in an MP4. Every piece of camcorder metadata AVCHD carries, including the recording timestamp and any clip information from the transport stream, is dropped. If the capture date matters, note it down before converting or keep the original file.

Will an AU file open on Windows or macOS?

Support is patchy and depends entirely on the player rather than the operating system. VLC and any ffmpeg-based tool open .au without complaint, as does anything built on Java's javax.sound.sampled, and audio editors such as Audacity import it. Several stock media players and web browsers do not. If you are sending the file to someone rather than feeding a specific tool, ask what they will open it with before you commit to the format.

Does dropping the sample rate to 8000 HZ actually sound like a phone call?

Fairly closely, yes, because that is the exact combination the telephone network standardised: G.711 mu-law at 8 kHz mono, 64 kbit/s. Halving the sample rate halves the audio bandwidth, so 8 kHz sampling caps the reproducible content at about 4 kHz and everything above that is discarded before encoding. Speech survives and stays intelligible; music does not. For camcorder audio that you actually want to listen to, leave the rate at ORIGINAL and accept the file size, or pick a compressed format instead.

How large a file can I upload, and how long is it kept?

There is no fixed per-file cap on our side; upload size and connection speed are what limit you in practice. AVCHD is a heavy format — the specification allows up to 24 Mbit/s, and 18 Mbit/s when recording to DVD media — so a long clip runs to several gigabytes and has to travel in full before conversion begins, even though only the audio is used. Everything you send goes over an encrypted connection, is converted on our servers, and both the upload and the output are deleted automatically after a few hours. Nothing is shared or made public and no account is required.