Convert 3GP to AU — Free Online Tool
Convert 3GP mobile video files to Sun AU audio format, extracting the audio stream and encoding it as 16-bit big-endian PCM — a lossless, uncompressed representation compatible with Unix systems and legacy audio pipelines. This tool strips the AAC or MP3 audio from your 3GP container and outputs a raw PCM AU file entirely in your browser, with no server upload required.
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FFmpeg Command
Copy this command to run the same conversion locally with FFmpeg on your desktop. Download FFmpeg
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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 video (H.264) alongside compressed audio encoded in AAC or MP3. The AU format is an audio-only container developed by Sun Microsystems that stores raw PCM data with a minimal header — it has no concept of video tracks. During this conversion, FFmpeg discards the video stream entirely and decodes the compressed audio from the 3GP file, then re-encodes it as 16-bit signed big-endian PCM (pcm_s16be). This is a lossy-to-lossless step in the audio domain: the original AAC or MP3 audio was already lossy, but the output AU file stores that decoded audio without any further compression artifacts. The result is a larger file than the original 3GP audio track but with no additional generation loss.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg command-line tool, which handles all media demuxing, decoding, encoding, and muxing in this conversion pipeline. |
-i input.3gp
|
Specifies the input file — a 3GP container typically holding H.264 video and AAC or MP3 audio as used on 3G mobile devices. FFmpeg will automatically detect and demux both streams. |
-c:a pcm_s16be
|
Sets the audio codec for the output to 16-bit signed big-endian PCM, the standard uncompressed audio encoding for the Sun AU format. This decodes the compressed AAC audio from the 3GP file into raw PCM samples without any further lossy compression. |
output.au
|
Specifies the output filename with the .au extension, which tells FFmpeg to use the Sun AU muxer. Since AU is an audio-only format, FFmpeg automatically discards the video stream from the 3GP input — no explicit video-drop flag is needed. |
Common Use Cases
- Extracting a voice memo or phone call recording saved in 3GP format on an older Android device for ingestion into a Unix-based audio processing pipeline that expects AU files
- Preparing audio from 3GP video clips for analysis with legacy Sun/NeXT audio tools or academic signal processing software that reads AU natively
- Converting mobile-captured 3GP audio to uncompressed PCM AU for use as a reference signal in audio quality comparison experiments, since AU's raw PCM eliminates codec variables
- Recovering intelligible audio from a 3GP file when video playback fails, outputting a simple AU file that nearly any Unix or macOS audio utility can open without codec dependencies
- Supplying uncompressed AU audio derived from 3GP recordings to older telephony or IVR systems that accept Sun AU as a native prompt format
- Archiving the audio content of 3GP mobile video into an uncompressed format before the original device or codec support becomes unavailable, preserving the decoded signal without further lossy compression
Frequently Asked Questions
No — the audio quality is bounded by whatever was recorded in the 3GP file originally. 3GP audio is typically encoded in AAC at low bitrates (often 64k or below) because the format was designed for 3G mobile networks with limited bandwidth. Converting to AU decodes that compressed audio into uncompressed PCM, which prevents any further quality degradation from re-encoding, but it cannot recover detail that AAC compression already discarded. Think of it as freezing the quality at its current state rather than improving it.
The 3GP container stores audio as compressed AAC or MP3, which can achieve compression ratios of 10:1 or more compared to raw PCM. The AU file stores audio as uncompressed 16-bit PCM at the full decoded sample rate, so a one-minute clip at 44.1 kHz stereo would occupy roughly 10 MB in AU format regardless of how small the original 3GP was. This size increase is expected and reflects the absence of any audio compression in the AU output.
The AU format supports several PCM variants (8-bit signed, 8-bit unsigned, 16-bit signed big-endian) as well as G.711 codecs like A-law and mu-law. This tool defaults to pcm_s16be — 16-bit signed big-endian PCM — because it offers the best balance of dynamic range and broad compatibility among AU-capable tools. Big-endian byte order is the historical standard for the Sun AU format, matching the byte order of SPARC-based Unix workstations where the format originated.
Yes. If you need G.711 mu-law or A-law encoding — common in telephony systems — you can modify the FFmpeg command by replacing 'pcm_s16be' with 'pcm_mulaw' or 'pcm_alaw' respectively. For example: ffmpeg -i input.3gp -c:a pcm_mulaw output.au. Mu-law encoding will produce a smaller file (8-bit samples) and is the standard format for many IVR and telephony prompt systems that accept AU files.
By default, FFmpeg preserves the sample rate of the source audio from the 3GP file, which is often 8000 Hz or 22050 Hz for mobile-recorded content. To resample to a specific rate, add the '-ar' flag before the output filename. For example, to output 44100 Hz audio: ffmpeg -i input.3gp -c:a pcm_s16be -ar 44100 output.au. Note that upsampling a low-rate 3GP recording to 44100 Hz will not add frequency content that was not captured originally.
The single-file command shown on this page must be run once per file, but you can easily wrap it in a shell loop for batch processing. On Linux or macOS: for f in *.3gp; do ffmpeg -i "$f" -c:a pcm_s16be "${f%.3gp}.au"; done. On Windows Command Prompt: for %f in (*.3gp) do ffmpeg -i "%f" -c:a pcm_s16be "%~nf.au". This is particularly useful for bulk-converting 3GP recordings from an older mobile device archive.
Technical Notes
The AU format's header is deliberately minimal — it stores the data offset, data size, encoding type, sample rate, and channel count, with no support for metadata fields like artist, title, or creation date. Any metadata embedded in your 3GP file (such as recording date or device information stored in MP4-style atoms) will be silently dropped during conversion, as AU has no mechanism to carry it. The 3GP format does not support transparency or subtitle tracks, so nothing is lost in that regard. Because 3GP was designed for constrained 3G networks, its audio is often recorded at reduced sample rates (8 kHz for voice, occasionally up to 22.05 kHz) with narrow dynamic range; the AU output will faithfully represent these characteristics. One practical concern: the AU format uses big-endian byte order, which means AU files created on little-endian x86 systems via FFmpeg are still written correctly (FFmpeg handles the byte-swapping), but some very old or non-standard AU parsers may struggle if they assume host byte order. For maximum compatibility with modern tools, WAV is generally preferred, but AU remains the correct choice for Unix legacy pipelines and telephony systems that expect it natively.