Convert 3G2 to AU — Free Online Tool
Convert 3G2 mobile video files to AU audio format, extracting and re-encoding the AAC or MP3 audio stream as uncompressed PCM (pcm_s16be) for use on Unix systems. This tool runs entirely in your browser via FFmpeg.wasm — no upload required.
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FFmpeg Command
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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
3G2 files are MPEG-4-based containers designed for CDMA mobile networks, typically carrying AAC or MP3 audio alongside H.264 video. AU is a headerless-simple audio container from Sun Microsystems that stores raw PCM audio data. During this conversion, FFmpeg discards the video stream entirely and decodes the compressed audio (AAC or MP3) from the 3G2 container, then re-encodes it as 16-bit big-endian signed PCM (pcm_s16be) — the default and most compatible AU codec. This is a full decode-and-re-encode of the audio, not a remux, because compressed audio like AAC cannot be stored natively in AU format. The result is a lossless PCM representation of the original lossy audio.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg binary — the underlying engine also used by FFmpeg.wasm in the browser. The same command runs identically on desktop FFmpeg installations for files over 1GB. |
-i input.3g2
|
Specifies the input file in 3G2 format — a MPEG-4-derived container used by CDMA mobile devices. FFmpeg reads both the H.264 video and AAC/MP3 audio streams from this container. |
-c:a pcm_s16be
|
Sets the audio codec to 16-bit signed big-endian PCM, which is the standard and most compatible encoding for the Sun AU format. This decodes the compressed AAC or MP3 audio from the 3G2 file into raw uncompressed samples stored in big-endian byte order. |
output.au
|
Defines the output filename with the .au extension, which tells FFmpeg to use the Sun AU muxer. The AU container wraps the pcm_s16be audio data with a minimal header describing sample rate, channels, and encoding type. |
Common Use Cases
- Extracting audio from old 3G2 video clips recorded on CDMA phones (e.g., early Verizon or Sprint handsets) for archival as uncompressed PCM on a Unix/Linux system
- Preparing audio from 3G2 mobile recordings for use in legacy Unix audio pipelines or tools like /dev/audio that expect raw Sun AU format
- Converting 3G2 voicemails or voice memos downloaded from early-2000s CDMA carrier portals into AU files for analysis or transcription on Unix workstations
- Feeding 3G2 audio into older Java applications or applets that rely on Sun's javax.sound API, which has native AU/pcm_s16be support
- Stripping video from 3G2 recordings and producing AU files as an intermediate uncompressed format before further processing in audio production tools on Unix or macOS
- Recovering audio from 3G2 footage captured on legacy mobile devices for use in academic or forensic audio workflows that require uncompressed big-endian PCM
Frequently Asked Questions
The output AU file will be an uncompressed PCM representation of the audio, but since the source audio in the 3G2 file is already lossy (typically AAC or MP3), some quality was already lost at recording time. The conversion from AAC/MP3 to pcm_s16be does not compress the audio further — it decodes it fully — so no additional lossy degradation occurs during this step. Think of it as 'freezing' the lossy audio in an uncompressed container.
3G2 files use efficient lossy compression codecs like AAC, which can achieve very small file sizes suitable for CDMA mobile networks. AU with pcm_s16be stores raw, uncompressed 16-bit audio samples — typically around 1.4 MB per minute per channel at 44.1 kHz. A 3G2 clip that was only a few hundred kilobytes can expand to several megabytes as an AU file because all compression is removed.
No. The Sun AU format has an extremely minimal header that stores only technical parameters: sample rate, channel count, encoding type, and an optional short annotation string. It has no support for ID3 tags, MP4 atoms, or any of the metadata fields that a 3G2 container may carry (such as recording date, location, or device info). All such metadata is lost during this conversion.
Yes. AU supports several PCM variants including pcm_mulaw (G.711 µ-law), pcm_alaw (G.711 A-law), pcm_s8, and pcm_u8 in addition to the default pcm_s16be. To use µ-law encoding for telephony compatibility, change the command to: ffmpeg -i input.3g2 -c:a pcm_mulaw output.au. Note that pcm_mulaw and pcm_alaw are lossy companding codecs commonly used in telecom, while pcm_s16be is lossless PCM.
On Linux or macOS, you can loop over all 3G2 files in a directory with: for f in *.3g2; do ffmpeg -i "$f" -c:a pcm_s16be "${f%.3g2}.au"; done. On Windows PowerShell: Get-ChildItem *.3g2 | ForEach-Object { ffmpeg -i $_.FullName -c:a pcm_s16be ($_.BaseName + '.au') }. This is particularly useful for large batches or files over 1GB, which exceed the browser tool's limit.
The video track is silently dropped. AU is a pure audio format with no container support for video streams, so FFmpeg automatically omits the H.264 or MJPEG video stream when writing to an AU output. You do not need to explicitly pass a -vn flag because the output format itself enforces audio-only. The resulting AU file contains only the decoded audio from the 3G2 source.
Technical Notes
The Sun AU format uses a simple fixed header followed by raw audio sample data, making it trivial to parse but very limited in capability. The default codec for this conversion, pcm_s16be, stores 16-bit signed samples in big-endian byte order — a legacy of Sun's SPARC architecture. This matters if you are consuming the AU file on a modern x86/ARM system (which is little-endian): most AU-aware libraries handle the byte-order conversion automatically, but raw byte-level reads will need to account for endianness. The 3G2 source typically encodes audio at 8–48 kHz; FFmpeg preserves the original sample rate and channel count in the AU output unless you specify -ar or -ac flags. There is no quality parameter meaningful for pcm_s16be — it is uncompressed and bit-for-bit accurate to whatever the AAC decoder produces. The AU format also has no support for multi-track audio, chapters, or subtitles, all of which are unsupported in 3G2 by this tool as well. If your 3G2 file was encoded at a very low sample rate (e.g., 8 kHz mono, common for CDMA voice), the resulting AU file will reflect that fidelity ceiling regardless of output settings.