Extract Audio from MOV to J2B — Free Online Tool
Extract audio from MOV video files and save it as J2B, the Jazz Jackrabbit 2 game audio format based on the ASYLUM Music Format. This tool strips the video stream and re-encodes the audio using the LAME MP3 encoder, outputting a J2B-wrapped MP3 file directly in your browser.
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FFmpeg Command
Copy this command to run the same conversion locally with FFmpeg on your desktop. Download FFmpeg
Drop your MOV 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
MOV files commonly carry AAC audio (Apple's default), though they also support MP3, FLAC, Opus, and Vorbis depending on how they were encoded. Since J2B uses MP3 (via the LAME encoder) as its underlying audio codec, the audio stream cannot simply be copied — it must be transcoded from whatever codec the MOV contains into MP3, then written with the J2B container header. The video stream is completely discarded using the -vn flag, and no video re-encoding takes place. The result is a J2B file whose inner audio data is LAME-encoded MP3 at 128k bitrate by default.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg binary. In the browser version this runs via FFmpeg.wasm (WebAssembly), so no installation is needed and no files leave your device. |
-i input.mov
|
Specifies the input QuickTime MOV file. FFmpeg will demux the container to access the separate video and audio streams, though only the audio will be used in this conversion. |
-vn
|
Disables video output entirely, telling FFmpeg to ignore and discard the video stream from the MOV file. This prevents any unnecessary video decoding and ensures the output J2B file contains only audio data. |
-c:a libmp3lame
|
Sets the audio encoder to LAME, producing MP3-encoded audio. This is required because J2B's underlying ASYLUM Music Format uses MP3 as its audio data, and MOV files most commonly carry AAC or other codecs incompatible with J2B. |
-b:a 128k
|
Sets the MP3 audio bitrate to 128 kilobits per second, which is the default for J2B output. This is a standard lossy quality level suitable for voice and moderate-fidelity music; increase to 256k or 320k for higher-quality game audio assets. |
output.j2b
|
Specifies the output filename with the .j2b extension. FFmpeg uses this extension to write the file with the J2B container header wrapping the LAME-encoded MP3 audio, producing a file compatible with Jazz Jackrabbit 2 level tooling. |
Common Use Cases
- Extracting a music or sound effect track from a MOV recording to import into a Jazz Jackrabbit 2 custom level as background music
- Converting a QuickTime audio demo or soundtrack clip into J2B format for use in JJ2 fan-made episode modding projects
- Stripping audio from a MOV screen capture of gameplay footage to create a J2B asset compatible with JJ2 level editors
- Re-packaging an Apple ProRes or H.264 MOV file's audio track into the J2B format for archival alongside other JJ2 game assets
- Quickly previewing what a MOV-sourced audio track will sound like under LAME MP3 compression before committing it to a JJ2 level package
Frequently Asked Questions
Yes, in most cases. If your MOV file contains AAC audio (Apple's default), transcoding to LAME MP3 at 128k involves converting from one lossy format to another, which introduces a second generation of compression artifacts. If your MOV contains FLAC or uncompressed audio, the quality loss is limited to the single MP3 encoding step. For best results with lossless source audio, consider increasing the bitrate to 256k or 320k in the FFmpeg command.
J2B is a proprietary audio container format used by Jazz Jackrabbit 2, a 1998 platformer game by Epic Games. It wraps the ASYLUM Music Format (AMF) with a simple file header. In modern usage, J2B files typically contain MP3 audio data, which is why FFmpeg uses the libmp3lame encoder to produce them. The format is niche and primarily relevant to JJ2 level modding and fan communities.
By default, FFmpeg selects the first (default) audio track from the MOV file. MOV containers do support multiple audio tracks, but J2B supports only a single audio stream. If you need to extract a specific non-default track from your MOV file, you can modify the FFmpeg command by adding '-map 0:a:1' (for the second audio track, zero-indexed) before the output filename.
The '-b:a 128k' flag controls the MP3 bitrate. You can replace '128k' with any supported value: 64k, 192k, 256k, or 320k. Higher bitrates produce better audio fidelity and larger files. For music content, 192k or 256k is typically a noticeable improvement over 128k. The command becomes: ffmpeg -i input.mov -vn -c:a libmp3lame -b:a 256k output.j2b
No. J2B does not support metadata, chapters, or subtitles — it is a minimal game audio container with no provision for such fields. Any chapter markers, album tags, or track titles embedded in the MOV file will be discarded during conversion. If metadata preservation matters, you should consider a more capable audio format instead.
The single-file command shown on this page processes one MOV at a time. To batch process on your desktop, you can use a shell loop — for example, on Linux or macOS: 'for f in *.mov; do ffmpeg -i "$f" -vn -c:a libmp3lame -b:a 128k "${f%.mov}.j2b"; done'. On Windows Command Prompt, use a for loop: 'for %f in (*.mov) do ffmpeg -i "%f" -vn -c:a libmp3lame -b:a 128k "%~nf.j2b"'. Batch processing is particularly useful for files over 1GB, which exceed the browser tool's limit.
Technical Notes
MOV is Apple's QuickTime container and commonly stores audio as AAC, which is not compatible with J2B's MP3-based internals — so transcoding via libmp3lame is mandatory regardless of source bitrate. The -vn flag ensures that no video decoder is invoked for the input's H.264, HEVC, or other video stream, making the process faster and purely audio-focused. J2B's ASYLUM Music Format wrapper is extremely lightweight, meaning the file size is almost entirely determined by the MP3 bitrate and audio duration. One known limitation is that J2B does not support stereo field metadata or multi-track layouts, so any surround or multi-channel audio in the MOV will be handled according to FFmpeg's default downmix behavior (typically folded to stereo). There is no lossless path to J2B since its only supported codec is lossy MP3. Users working with professionally recorded MOV audio (e.g., from Final Cut Pro workflows) should be aware that the AAC-to-MP3 transcode will introduce artifacts even at high bitrates, and sourcing from a lossless intermediate if available is advisable.