Extract Audio from 3G2 to J2B — Free Online Tool
Extract audio from 3G2 mobile video files and convert it to J2B format using the LAME MP3 encoder. This tool strips the AAC or MP3 audio stream from the CDMA-era 3G2 container and re-encodes it as a J2B file — the ASYLUM Music Format wrapper used by Jazz Jackrabbit 2 — entirely in your browser with no upload required.
to
FFmpeg Command
Copy this command to run the same conversion locally with FFmpeg on your desktop. Download FFmpeg
Drop your 3G2 file here
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Settings
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 store audio using either AAC or MP3 (via libmp3lame), optimized for low-bitrate transmission over CDMA mobile networks. During this conversion, FFmpeg discards the video stream entirely and re-encodes the audio using the LAME MP3 encoder (libmp3lame) at 128k bitrate by default. The resulting audio is wrapped in the J2B container format, which is a lightweight header around the ASYLUM Music Format used by the Jazz Jackrabbit 2 game engine. Because 3G2 audio is often AAC and J2B requires MP3, transcoding always occurs — this is not a lossless remux. The output inherits the audio content from the 3G2 source but loses any mobile-streaming metadata specific to the 3GPP2 container.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg tool, which handles all demuxing, decoding, re-encoding, and muxing steps for this 3G2-to-J2B audio extraction in a single pass. |
-i input.3g2
|
Specifies the input 3G2 file — a 3GPP2 multimedia container typically holding H.264 video and AAC or MP3 audio recorded on CDMA mobile devices. |
-vn
|
Disables video output entirely, ensuring that only the audio stream from the 3G2 file is processed and that no video data is passed to the J2B output, which is an audio-only format. |
-c:a libmp3lame
|
Selects the LAME MP3 encoder to re-encode the audio extracted from the 3G2 file. Since J2B requires MP3-compatible audio and the 3G2 source is typically AAC, transcoding through libmp3lame is mandatory rather than optional. |
-b:a 128k
|
Sets the MP3 output bitrate to 128 kilobits per second — a moderate quality level that balances file size against audio fidelity. Since 3G2 audio is often encoded at low bitrates for mobile networks, 128k is generally sufficient to represent the available source quality. |
output.j2b
|
Specifies the output filename with the .j2b extension, instructing FFmpeg to write the re-encoded MP3 audio into a J2B-wrapped file compatible with Jazz Jackrabbit 2 tooling and ASYLUM Music Format consumers. |
Common Use Cases
- Recovering game-compatible audio from 3G2 video clips to create custom music tracks for Jazz Jackrabbit 2 mods or community levels
- Extracting mobile-captured audio from old CDMA phone recordings stored in 3G2 format for use in retro game projects that accept J2B files
- Converting archived 3G2 field recordings or sound effects into J2B for integration into Jazz Jackrabbit 2 fan-made episode soundtracks
- Stripping the audio layer from 3G2 promotional or demo videos to reuse the music content in J2B-compatible game modding tools
- Batch-preparing a library of 3G2 audio sources into J2B format for a retro game preservation project that uses the ASYLUM Music Format
- Generating the exact FFmpeg command to automate 3G2-to-J2B audio extraction locally for large files or batch workflows beyond the 1GB browser limit
Frequently Asked Questions
Yes, this is a lossy-to-lossy conversion in most cases. If the 3G2 file contains AAC audio (the default codec for 3G2), the audio must be decoded and then re-encoded as MP3 using the LAME encoder, which introduces a second generation of compression artifacts. If the 3G2 already uses MP3 audio internally, re-encoding to MP3 again still degrades quality slightly. To minimize quality loss, increase the output bitrate in the FFmpeg command using '-b:a 256k' or '-b:a 320k'.
J2B is specifically the ASYLUM Music Format with a simple header, designed for the Jazz Jackrabbit 2 game engine's tracker-style music system. Audio extracted from a 3G2 file is PCM/MP3-style linear audio, not tracker module data, so the resulting J2B file will be structurally non-standard and is unlikely to play correctly in the JJ2 game engine itself. This conversion is more useful for modding tools or custom engines that accept J2B as a generic audio wrapper rather than for direct in-game playback.
J2B is a pure audio format with no support for video streams, so the video is intentionally discarded. The '-vn' flag in the FFmpeg command explicitly instructs FFmpeg to ignore all video streams from the 3G2 input. Even without '-vn', FFmpeg would reject the video since J2B has no video codec container support.
Adjust the '-b:a 128k' flag to your desired bitrate. J2B via libmp3lame supports 64k, 128k, 192k, 256k, and 320k. For example, use '-b:a 320k' for the highest MP3 quality or '-b:a 64k' to produce a smaller file closer to the low-bitrate spirit of the original 3G2 mobile format. The full modified command would be: ffmpeg -i input.3g2 -vn -c:a libmp3lame -b:a 320k output.j2b
No. 3G2 files often contain 3GPP2-specific metadata such as device information, GPS tags, and mobile network flags stored in atoms like 'moov' and 'udta'. The J2B format has no equivalent metadata structure — it uses only a minimal fixed-length header wrapping the audio data. All mobile-specific metadata is discarded during this conversion.
Yes. You can adapt the displayed command into a shell loop for batch processing. On Linux or macOS, use: for f in *.3g2; do ffmpeg -i "$f" -vn -c:a libmp3lame -b:a 128k "${f%.3g2}.j2b"; done. On Windows Command Prompt: for %f in (*.3g2) do ffmpeg -i "%f" -vn -c:a libmp3lame -b:a 128k "%~nf.j2b". This is especially practical for collections of archived CDMA phone recordings that exceed the browser tool's 1GB limit.
Technical Notes
3G2 was designed for CDMA networks (used by carriers like Verizon and Sprint) and typically stores audio as AAC at low bitrates — often 64k or below — to minimize data transmission costs. When extracting to J2B, the AAC audio is fully decoded and re-encoded by the LAME MP3 encoder, meaning the output quality is bounded by the source bitrate: a 64k AAC source re-encoded at 128k MP3 will not recover detail that was lost in the original 3G2 encoding. The J2B format itself is structurally simple — a 4-byte magic header ('MUSE') followed by version and data length fields, then raw ASYLUM module data — though in this FFmpeg workflow the output is essentially MP3 audio data with a J2B file extension, not a true tracker module. FFmpeg does not have a native J2B muxer and writes the audio stream using libmp3lame without strict ASYLUM format compliance, so compatibility depends entirely on the consuming application's tolerance for non-module J2B data. No chapter markers, subtitle tracks, or multiple audio streams are supported by either format in this conversion path.