Extract Audio from 3GP to AU — Free Online Tool
Extract audio from 3GP mobile video files and save it as Sun AU format with PCM 16-bit big-endian encoding. This tool strips the AAC or MP3 audio track from your 3GP container and re-encodes it as uncompressed PCM audio, producing a lossless-quality AU file compatible with Unix systems and legacy audio toolchains.
to
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
3GP files typically contain AAC-encoded audio (occasionally MP3) alongside H.264 video, compressed for low-bandwidth mobile delivery. This conversion discards the video stream entirely and decodes the compressed audio, then re-encodes it as PCM 16-bit big-endian (pcm_s16be) — the default and most compatible codec for the AU container. Because the 3GP audio is lossy (AAC or MP3) and the output is uncompressed PCM, the AU file will not recover any quality lost during the original mobile encoding, but it will be a faithful, uncompressed representation of whatever audio was stored in the 3GP file. The resulting AU file uses Sun's simple fixed header structure, making it immediately readable by Unix audio utilities, Java's AudioInputStream, and many legacy tools without any additional decoding step.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg command-line tool. In the browser version of this tool, this runs via FFmpeg.wasm (WebAssembly) entirely within your browser — no data is sent to a server. |
-i input.3gp
|
Specifies the input 3GP file. FFmpeg will detect the container as 3GPP and demux the contained streams, which typically include an H.264 video track and an AAC audio track compressed for mobile delivery. |
-vn
|
Disables video output entirely, discarding the H.264 (or MJPEG) video stream from the 3GP file. This is required because the AU format has no video codec support, and omitting this flag would cause FFmpeg to fail when attempting to write video data. |
-c:a pcm_s16be
|
Decodes the 3GP's compressed AAC audio and re-encodes it as 16-bit signed PCM in big-endian byte order — the native and default audio codec for the Sun AU format, ensuring maximum compatibility with Unix audio tools and Java's sound API. |
output.au
|
Sets the output filename with the .au extension, which tells FFmpeg to write the Sun AU container format. The resulting file will have a simple AU header describing the PCM encoding, sample rate, and channel count inherited from the source 3GP audio stream. |
Common Use Cases
- Loading audio from old 3GP mobile recordings into Unix-based audio processing pipelines or legacy Sun workstation software that expects AU files
- Extracting voice memos or phone recordings saved in 3GP format to feed into Java applications that natively support the AU format via javax.sound.sampled
- Converting 3GP audio to uncompressed PCM AU for use as input to scientific or academic audio analysis tools that require raw, uncompressed waveform data
- Archiving the audio track from 3GP mobile video clips in a simple, headerless-compatible PCM format that avoids codec dependency issues over long-term storage
- Preparing audio extracted from 3GP footage for use in early web or multimedia authoring tools (such as HyperCard or NeXT-era applications) that were built around the AU format
- Stripping video from 3GP clips to isolate spoken dialogue or field recordings as uncompressed AU files before importing into a professional audio workstation
Frequently Asked Questions
No. The audio in a 3GP file is typically encoded as AAC at a low bitrate (often 64kbps or less) optimized for mobile bandwidth constraints. Converting to AU with PCM encoding produces an uncompressed file, but it cannot recover the frequency and detail information that was discarded during the original AAC compression. The AU file will be an accurate, uncompressed copy of the decoded AAC audio — no better and no worse in perceptual quality than the source 3GP audio.
3GP uses AAC audio compression, which typically achieves 10:1 to 20:1 size reduction compared to uncompressed audio. The AU output uses PCM 16-bit big-endian encoding, which is completely uncompressed — every audio sample is stored as a raw integer. A 3GP clip with 64kbps AAC audio will produce an AU file at roughly 1411kbps (CD-quality stereo), making the audio portion alone many times larger. The absence of the video stream partially offsets this, but expect the AU file to be significantly larger than the 3GP source.
Yes. The AU format supports several PCM variants beyond the default pcm_s16be, including pcm_mulaw (µ-law), pcm_alaw (A-law), pcm_s8 (signed 8-bit), and pcm_u8 (unsigned 8-bit). To use µ-law encoding, modify the command to: ffmpeg -i input.3gp -vn -c:a pcm_mulaw output.au. µ-law and A-law are lossy companding formats historically used in telephony and will produce smaller files, which may be appropriate if you need AU files compatible with specific telecom or legacy Unix audio applications.
The Sun AU format has an extremely minimal header — it stores sample rate, channel count, encoding type, and an optional annotation field, but has no standardized support for metadata tags like artist, title, or date. Any ID3-style or 3GPP metadata embedded in the source 3GP file (such as title or author tags) will not be carried over to the AU output. If metadata preservation is important, a format like FLAC or WAV would be a better uncompressed target.
By default, FFmpeg preserves the original sample rate from the 3GP audio stream (commonly 8000 Hz or 44100 Hz for mobile recordings). To resample the output, add the -ar flag before the output filename. For example: ffmpeg -i input.3gp -vn -c:a pcm_s16be -ar 44100 output.au will force 44.1kHz output, while -ar 8000 will downsample to telephony-grade 8kHz. Note that upsampling a low-quality 3GP recording will not add audio fidelity.
On Linux or macOS, you can use a shell loop: 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 applies the exact same extraction and PCM encoding to every 3GP file in the directory, outputting a matching AU file for each one.
Technical Notes
The Sun AU format uses a big-endian byte order, which aligns with its origins on SPARC-based Sun workstations — FFmpeg's pcm_s16be codec matches this natively without any byte-swapping workaround. Because 3GP was designed for 3G mobile networks, its audio streams are frequently low sample-rate (8kHz or 16kHz) mono AAC, especially in voice recordings; the resulting AU file will inherit these constraints, meaning the output may sound narrow or telephone-quality regardless of codec. The AU format has no support for multi-channel audio beyond stereo, but this is rarely a concern given that 3GP itself does not support multiple audio tracks. One known limitation is that AU files lack a standardized way to store loop points, cue markers, or chapter data — none of which 3GP supports anyway. The -vn flag is essential here to explicitly suppress video output, since FFmpeg would otherwise attempt to find a video codec compatible with AU, which has none, and error out. For very long 3GP recordings, be aware that the uncompressed AU output has no internal indexing, so seeking in large AU files may be slow in some playback tools.