Convert M2TS to J2B — Free Online Tool
Convert M2TS Blu-ray video files to J2B game audio format, extracting and encoding only the audio stream as MP3 using the LAME encoder. This niche conversion strips the high-definition video and multichannel audio from a BDAV transport stream down to a single compressed MP3 track compatible with the Jazz Jackrabbit 2 ASYLUM Music Format container.
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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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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
M2TS is a BDAV MPEG-2 Transport Stream container typically carrying H.264 or H.265 video alongside high-bitrate audio such as AC-3, DTS, or TrueHD — often in multiple tracks. J2B is an audio-only format used by Jazz Jackrabbit 2, consisting of an MP3 stream wrapped in a lightweight ASYLUM Music Format header. During this conversion, FFmpeg completely discards the video stream and any subtitle or secondary audio tracks, then re-encodes the primary audio track from its original codec (whatever the M2TS source carries) into MP3 using the libmp3lame encoder at 128k bitrate. Because J2B supports only a single mono or stereo MP3 track, any surround or multichannel audio in the M2TS source is automatically downmixed to stereo during the transcode.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg multimedia processing tool. In the browser this runs via FFmpeg.wasm (WebAssembly), but the command is identical to what you would run in a local terminal on Windows, macOS, or Linux. |
-i input.m2ts
|
Specifies the input file — an M2TS Blu-ray BDAV transport stream, which may contain H.264/H.265 video, multichannel audio (TrueHD, DTS-HD, AC-3, etc.), subtitles, and multiple audio tracks. |
-c:a libmp3lame
|
Selects the LAME MP3 encoder for the audio stream. This is required because J2B stores its audio payload as MP3, and libmp3lame is the standard high-quality MPEG Layer 3 encoder available in FFmpeg. |
-b:a 128k
|
Sets the MP3 audio bitrate to 128 kilobits per second — the J2B default, balancing file size and audio quality for the game audio context. You can raise this to 192k, 256k, or 320k for higher fidelity if the M2TS source audio warrants it. |
output.j2b
|
Specifies the output filename with the .j2b extension, which signals FFmpeg to write the MP3 audio payload wrapped in the ASYLUM Music Format header structure expected by the Jazz Jackrabbit 2 game engine. |
Common Use Cases
- Extracting a musical score or theme recorded on a Blu-ray disc and packaging it in J2B format for use as a custom soundtrack in a Jazz Jackrabbit 2 mod or level pack.
- Converting AVCHD camcorder footage (.m2ts) of a live music performance to a J2B file to use the audio as background music in a JJ2 custom episode.
- Pulling dialog or sound effect clips from a Blu-ray rip in M2TS format and wrapping them as J2B assets for a fan-made Jazz Jackrabbit 2 game modification.
- Archiving or cataloguing audio content from Blu-ray-sourced M2TS files into J2B as an experimental or novelty retro game audio format.
- Testing how high-quality M2TS audio sources degrade when transcoded to the lossy MP3 encoding pipeline used by the J2B format at various bitrates.
Frequently Asked Questions
No — J2B is a strictly audio-only format based on the ASYLUM Music Format used by Jazz Jackrabbit 2, so it has no capacity to store video data whatsoever. FFmpeg automatically drops the video stream during this conversion. If you need to keep the video, J2B is not an appropriate output format and you should choose a container that supports both video and audio.
FFmpeg will decode whichever audio codec the M2TS carries — including lossless or lossy surround formats like TrueHD, DTS-HD MA, AC-3, or PCM — and then re-encode it to MP3 stereo using libmp3lame. Because J2B supports only a single stereo (or mono) MP3 track, any 5.1 or 7.1 surround channels will be automatically downmixed to two channels during the transcode. This is an inherent limitation of the J2B target format.
The degree of quality loss depends on the source audio codec in the M2TS. If the source carries lossless audio (TrueHD, PCM, DTS-HD MA), transcoding to MP3 at 128k introduces the compression artifacts typical of mid-bitrate MPEG Layer 3 encoding — audible to critical listeners, but generally acceptable for background game music. If the source is already lossy (AC-3, DTS core), you are performing a generation-loss transcode, which compounds compression artifacts. For the highest quality J2B output, use the 320k bitrate option if your source is high-quality.
Yes — the bitrate is controlled by the -b:a flag in the command. Replace '128k' with any value supported by J2B and libmp3lame: 64k, 128k, 192k, 256k, or 320k. For example, use '-b:a 320k' for the highest quality MP3 output. Keep in mind that J2B files are intended for a retro game engine, so extremely high bitrates may not be perceptible in that playback context and will simply increase file size.
None of these will be carried over. J2B does not support chapters, subtitles, or multiple audio tracks — it is a single-stream audio format. FFmpeg will select only the first (or best-ranked) audio stream from the M2TS and encode that to MP3. All other streams, including subtitles, alternate language tracks, and commentary tracks, are silently discarded.
Yes — on Linux or macOS you can use a shell loop: 'for f in *.m2ts; do ffmpeg -i "$f" -c:a libmp3lame -b:a 128k "${f%.m2ts}.j2b"; done'. On Windows Command Prompt the equivalent is: 'for %f in (*.m2ts) do ffmpeg -i "%f" -c:a libmp3lame -b:a 128k "%~nf.j2b"'. This processes each M2TS file in the current directory and writes a corresponding J2B file. Note that the in-browser tool handles one file at a time.
Technical Notes
J2B is an obscure, game-specific audio container tied to Jazz Jackrabbit 2, built on the ASYLUM Music Format with a simple binary header wrapping an MP3 payload. FFmpeg can write this format via the libmp3lame encoder, but support is limited compared to mainstream audio containers — no metadata tags (ID3 or otherwise), no chapter markers, and no multi-track capability are preserved from the M2TS source. The M2TS container commonly carries multiple audio streams (e.g., a primary TrueHD 7.1 track plus an AC-3 compatibility track), but FFmpeg will select only the default or highest-priority stream for the J2B output. The original M2TS audio codec must be fully decoded before re-encoding to MP3, meaning this is always a full transcode — there is no possibility of stream copying. File sizes will be dramatically smaller than the source M2TS because all video data is removed and audio is compressed to a low-overhead MP3 stream; a typical Blu-ray M2TS of several gigabytes will yield a J2B file of only a few megabytes. Users processing M2TS files larger than 1GB should use the desktop FFmpeg command directly, as the browser tool is optimized for files under that threshold.