Extract Audio from 3GPP to AU — Free Online Tool
Extract audio from 3GPP mobile video files and convert it to Sun AU format using PCM 16-bit big-endian encoding. This tool strips the AAC or MP3 audio track from your 3GP file and re-encodes it as uncompressed PCM audio in the classic Unix AU container — useful for legacy Unix/Linux workflows and audio processing pipelines that expect raw PCM data.
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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
3GPP files typically carry AAC-compressed audio alongside H.264 video, both designed for low-bandwidth mobile delivery. During this conversion, the video stream is completely discarded and the compressed AAC (or MP3) audio is decoded to raw PCM samples, then re-encoded as 16-bit signed big-endian PCM and wrapped in the Sun AU container. This is a full audio transcode — not a remux — because AU's native codec (pcm_s16be) is fundamentally different from the lossy codecs used in 3GP. The result is uncompressed audio, which will be significantly larger than the original 3GP audio track but introduces no further lossy compression artifacts beyond those already baked into the source.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg tool, which handles all demuxing, decoding, encoding, and muxing. In this browser-based tool, FFmpeg runs locally via WebAssembly (FFmpeg.wasm) — your 3GP file never leaves your device. |
-i input.3gp
|
Specifies the input 3GPP file. FFmpeg reads the 3GP container, identifies the video stream (typically H.264) and audio stream (typically AAC), and makes both available for processing. |
-vn
|
Disables video output entirely, discarding the H.264 (or MJPEG) video stream from the 3GP file. Since AU is an audio-only format, this flag is required — without it, FFmpeg would attempt to write a video stream into a container that cannot hold one. |
-c:a pcm_s16be
|
Decodes the compressed AAC audio from the 3GP file and re-encodes it as 16-bit signed big-endian PCM — the native and most compatible audio codec for the Sun AU format, matching the big-endian byte order convention of AU's Unix/SPARC origins. |
output.au
|
Sets 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 fixed header describing the sample rate, bit depth, and channel count extracted from the source 3GP audio stream. |
Common Use Cases
- Extracting voice recordings or voice memos captured on older mobile phones in 3GP format to feed into Unix-based audio analysis or transcription tools that accept AU files
- Converting 3GP audio from legacy mobile video archives into AU format for use with Sun/Oracle audio tools or older Unix multimedia software that predates MP3/AAC support
- Preparing 3GP-sourced audio for use in Java applications, which have historically had native AU format support through the Java Sound API
- Extracting and uncompressing audio from 3G-era mobile video clips for forensic audio analysis, where PCM data is required to avoid lossy re-encoding artifacts
- Migrating audio content from a mobile device's 3GP recordings into a Unix workstation's audio pipeline where AU is the expected interchange format
- Decoding compressed 3GP audio to PCM AU as an intermediate step before applying DSP processing tools that require raw uncompressed samples
Frequently Asked Questions
No — the audio quality ceiling is set by the original 3GP file, which typically contains AAC audio encoded at low bitrates (often 32–64 kbps) optimized for 3G mobile networks. Converting to AU decompresses that AAC audio into PCM, which means no additional lossy compression is applied, but the artifacts already introduced during the original AAC encoding are permanently embedded in the audio data. The AU file will be larger and uncompressed, but it won't sound better than the source.
3GP files store audio in AAC or MP3 format, which achieve compression ratios of roughly 10:1 or more compared to raw PCM. The AU file stores audio as uncompressed 16-bit PCM at the original sample rate, so a 1-minute 3GP audio track at 64 kbps (~0.5 MB) becomes approximately 5–10 MB in AU format depending on the sample rate. This size increase is expected and is the nature of converting from lossy-compressed to uncompressed PCM audio.
The Sun AU format supports several PCM variants (16-bit signed big-endian, 8-bit signed, 8-bit unsigned) as well as G.711 codecs (A-law and mu-law). This tool defaults to pcm_s16be — 16-bit signed big-endian PCM — because it provides the best dynamic range and broadest compatibility among AU-aware software. The big-endian byte order is native to the AU format's Sun SPARC origins and is the standard expectation for AU files on Unix systems.
Yes. If you need mu-law or A-law encoding (common in telephony and VoIP contexts), you can replace pcm_s16be in the command with pcm_mulaw or pcm_alaw: ffmpeg -i input.3gp -vn -c:a pcm_mulaw output.au. These are lossy 8-bit companded formats that produce smaller files and are well-suited for voice, which aligns with the speech-focused content typical of 3GP recordings. The AU container natively supports all these codec variants.
Very little metadata survives this conversion. AU is an extremely minimal format — its header contains only basic fields like data offset, data size, encoding type, sample rate, and channels, with a limited annotation field. The rich metadata atoms (title, artist, date, GPS tags) found in 3GP's MP4-derived container structure have no equivalent fields in AU and are discarded during conversion. If preserving metadata is important, consider an intermediate format like FLAC or WAV before archiving.
On Linux or macOS, you can use a shell loop to batch process files: for f in *.3gp; do ffmpeg -i "$f" -vn -c:a pcm_s16be "${f%.3gp}.au"; done. On Windows Command Prompt, use: for %f in (*.3gp) do ffmpeg -i "%f" -vn -c:a pcm_s16be "%~nf.au". This is especially useful when migrating a large archive of mobile recordings, since the browser-based tool processes one file at a time.
Technical Notes
The 3GPP container is a profile of MPEG-4 Part 12, and its audio is almost universally AAC (specifically AAC-LC at low bitrates) when produced by mobile devices, though some older 3GP files carry AMR-NB or AMR-WB audio rather than AAC or MP3. If your source 3GP contains AMR audio, FFmpeg will still decode it correctly during this conversion, but be aware that AMR codec audio sampled at 8 kHz will produce a AU file with an 8 kHz sample rate — reflected in the AU header — and the resulting audio may sound narrowband. The AU format itself has no inherent sample rate limitation, so the output sample rate will match whatever the source stream carried. One notable limitation is that AU does not support multiple channels beyond stereo in a standard way, and most 3GP mobile audio is mono anyway. The -vn flag is essential here since AU is a pure audio format and cannot contain video streams. No special container flags are needed for AU — unlike MP4/3GP which require -movflags +faststart for streaming — because AU's header is written at the start of the file by default.