Extract Audio from 3GP to J2B — Free Online Tool
Extract audio from 3GP mobile video files and save it as J2B, the ASYLUM Music Format-based audio container used by Jazz Jackrabbit 2. The tool decodes the AAC audio track from your 3GP file and re-encodes it to MP3 using the LAME encoder, producing a J2B-compatible output entirely in your browser.
to
FFmpeg Command
Copy this command to run the same conversion locally with FFmpeg on your desktop. Download FFmpeg
Drop your 3GP 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
3GP files store audio using AAC (Advanced Audio Coding) by default, optimized for the low-bandwidth constraints of 3G mobile networks. J2B is a niche game audio format used by Jazz Jackrabbit 2, built on the ASYLUM Music Format with a simple wrapper header, and it uses MP3 as its underlying audio encoding. Because AAC and MP3 are two different lossy codecs, this conversion cannot simply copy the audio stream — FFmpeg must fully decode the AAC audio from the 3GP container and then re-encode it using the LAME MP3 encoder at 128k bitrate into the J2B output file. The video stream in the 3GP file is discarded entirely using the -vn flag. Since both the source and destination codecs are lossy, this is a lossy-to-lossy transcode, meaning some additional audio quality degradation is expected compared to transcoding from a lossless source.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg tool, which is running here as FFmpeg.wasm compiled to WebAssembly and executed entirely inside your browser — no data leaves your device during this conversion. |
-i input.3gp
|
Specifies the input file, a 3GP mobile video container that typically holds H.264 video and AAC audio encoded at low bitrates for 3G network delivery. |
-vn
|
Disables video output entirely, instructing FFmpeg to skip the H.264 video stream in the 3GP file and produce an audio-only result, which is required since J2B is a pure audio format. |
-c:a libmp3lame
|
Selects the LAME MP3 encoder to re-encode the audio, transcoding the AAC audio track from the 3GP source into MP3, which is the audio codec required by the J2B format used in Jazz Jackrabbit 2. |
-b:a 128k
|
Sets the MP3 output audio bitrate to 128 kilobits per second, a standard quality level for LAME-encoded MP3 that balances file size and fidelity; given typical 3GP source bitrates of 32k–96k AAC, 128k MP3 represents a reasonable ceiling for perceptible quality. |
output.j2b
|
Defines the output filename with the .j2b extension, signaling the Jazz Jackrabbit 2 audio format; FFmpeg writes the LAME-encoded MP3 audio into this file for use with JJ2-compatible game audio tools or level editors. |
Common Use Cases
- Extracting the audio track from an old 3GP mobile phone video to repurpose it as a custom music or sound file for Jazz Jackrabbit 2 modding projects
- Converting a 3GP field recording or voice memo captured on a legacy 3G handset into a J2B file for integration into a JJ2 level or fan-made game mod
- Archiving or experimenting with the ASYLUM Music Format by feeding real-world audio from 3GP mobile clips into J2B containers for research or retro game development
- Preparing a short musical clip recorded on a mobile device in 3GP format for use as background music in a Jazz Jackrabbit 2 custom level pack
- Testing J2B audio output pipelines using readily available 3GP source files from older Android or Nokia devices before committing to a full retro game audio workflow
- Stripping the video from a 3GP clip captured on a 3G phone to isolate a sound effect or jingle for use in a J2B-compatible game engine context
Frequently Asked Questions
Yes, some quality loss is inevitable because this is a lossy-to-lossy transcode. The original AAC audio in the 3GP file is already compressed, and re-encoding it to MP3 via LAME introduces a second round of lossy compression artifacts. The default 128k bitrate is reasonable for MP3 and will produce acceptable results for most audio, but if your 3GP source was already encoded at a very low bitrate (such as 32k or 48k, common on 3G mobile devices), the output quality will be limited by the source regardless of the output bitrate you choose.
J2B is tied to the Jazz Jackrabbit 2 game engine, which was developed in the late 1990s when MP3 was the dominant compressed audio format and AAC did not yet exist in widespread use. The ASYLUM Music Format at the core of J2B predates AAC entirely, and the J2B wrapper inherits this MP3 dependency. This is a format constraint of the game's audio system, not a quality decision — so even though AAC is technically more efficient than MP3, J2B files must use LAME-encoded MP3 audio.
The video stream is completely discarded. The -vn flag in the FFmpeg command instructs FFmpeg to ignore all video streams in the 3GP input and produce an audio-only output. 3GP video is typically encoded with H.264 (libx264), which has no place in a J2B audio file, so stripping it is both necessary and correct. Only the audio track is decoded and re-encoded into the J2B output.
Replace the -b:a 128k value in the command with a higher bitrate supported by the J2B format, such as 192k, 256k, or 320k. For example: ffmpeg -i input.3gp -vn -c:a libmp3lame -b:a 320k output.j2b. Keep in mind that because the 3GP source uses AAC at typically low mobile bitrates (often 64k or below), increasing the MP3 output bitrate beyond the effective quality of the source will increase file size without meaningfully recovering lost detail. A bitrate of 128k to 192k is usually the practical ceiling for 3GP-sourced audio.
The command as shown processes a single file, but you can batch process using a shell loop. On Linux or macOS, use: for f in *.3gp; do ffmpeg -i "$f" -vn -c:a libmp3lame -b:a 128k "${f%.3gp}.j2b"; done. On Windows Command Prompt, use: for %f in (*.3gp) do ffmpeg -i "%f" -vn -c:a libmp3lame -b:a 128k "%~nf.j2b". This is especially useful if you have a collection of old 3G phone clips you want to convert in bulk for a modding project.
Generally no. 3GP files can carry metadata in their MP4-style container atoms, but J2B is a minimal format based on the ASYLUM Music Format with a simple binary header designed for game engine use, not general metadata storage. FFmpeg will not map 3GP metadata tags into the J2B output in any meaningful way. If preserving audio metadata is important, consider an intermediate format like MP3 or OGG instead, as J2B is purpose-built for Jazz Jackrabbit 2 and lacks standard metadata support.
Technical Notes
3GP is a subset of the MPEG-4 container format designed for 3G mobile networks, and its audio tracks are almost universally AAC-encoded at low bitrates (32k–96k) to minimize file size for mobile storage and streaming constraints. J2B, by contrast, is a highly niche format tied specifically to Jazz Jackrabbit 2; it wraps the ASYLUM Music Format in a short proprietary header and expects MP3-encoded audio from the LAME encoder. Because FFmpeg does not have native, well-documented J2B container support as a general multimedia format, the output file is produced by encoding the audio with libmp3lame and writing it with the .j2b extension — compatibility with the Jazz Jackrabbit 2 engine depends on whether the game or a compatible player correctly parses the ASYLUM header. The conversion is fully lossy at both ends: AAC decoding introduces no additional loss, but LAME re-encoding will add generation loss on top of the existing AAC compression. Users working on JJ2 modding should be aware that the ASYLUM Music Format was originally designed for tracker-style module music (similar to .mod or .it files), and using a straight MP3 extraction in a J2B wrapper may or may not behave identically to natively authored J2B files depending on the game version and any mods or loaders in use.