Extract Audio from M2TS to J2B — Free Online Tool
Extract audio from M2TS Blu-ray and AVCHD files and save it as a J2B file encoded with the LAME MP3 engine. This tool strips the video stream entirely and re-encodes only the audio track using libmp3lame at 128k bitrate — running fully in your browser with no uploads required.
to
FFmpeg Command
Copy this command to run the same conversion locally with FFmpeg on your desktop. Download FFmpeg
Drop your M2TS 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
M2TS files are MPEG-2 Transport Stream containers most commonly found on Blu-ray discs and AVCHD camcorders. They typically carry high-definition video alongside audio encoded in AAC, AC-3, DTS, or TrueHD. J2B is a highly niche audio format tied to the Jazz Jackrabbit 2 game engine — it wraps audio in the ASYLUM Music Format header and expects MP3-encoded audio via libmp3lame. Because J2B does not support video, the conversion process discards the video stream entirely using the -vn flag and re-encodes the first audio track from whatever codec it was stored in within the M2TS container into MP3 using the LAME encoder. This is a full audio transcode, not a remux — the audio data is decoded and then re-encoded, which involves some quality loss inherent to the lossy MP3 format.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg binary. In this browser tool, it runs as a WebAssembly module (FFmpeg.wasm) entirely client-side — no data leaves your machine. When running locally on your desktop, this calls your installed FFmpeg executable. |
-i input.m2ts
|
Specifies the input M2TS file — the Blu-ray BDAV or AVCHD transport stream container. FFmpeg will read and demux all streams it contains, including video, audio, and any subtitle tracks, making them available for the subsequent processing flags. |
-vn
|
Disables video output entirely. Since J2B is an audio-only format, this flag ensures FFmpeg does not attempt to encode or include any of the M2TS video streams in the output, saving processing time and producing a valid audio-only J2B file. |
-c:a libmp3lame
|
Instructs FFmpeg to re-encode the audio stream using the LAME MP3 encoder. This is mandatory for J2B output since the format is built around MP3 audio wrapped in an ASYLUM Music Format header — no other codec is compatible with the J2B container. |
-b:a 128k
|
Sets the MP3 audio bitrate to 128 kilobits per second. This is the default for J2B output and provides a reasonable balance between file size and audio quality. It can be increased to 256k or 320k on the command line if higher fidelity is needed from the M2TS source audio. |
output.j2b
|
Defines the output filename with the .j2b extension. FFmpeg uses this extension to confirm the target format, and the resulting file will contain LAME-encoded MP3 audio wrapped in the J2B ASYLUM Music Format header, suitable for use with Jazz Jackrabbit 2 and compatible tools. |
Common Use Cases
- Extracting dialogue or ambient sound from Blu-ray rips to use as audio assets in Jazz Jackrabbit 2 custom levels or mods
- Converting AVCHD camcorder footage audio into a J2B-compatible MP3 stream for retro game audio hobbyist projects
- Pulling a specific audio track from a multi-audio-track M2TS broadcast recording to feed into J2B-based toolchains
- Archiving the audio layer of an M2TS video file in a compact lossy format when the video content is no longer needed
- Testing J2B playback pipelines by generating J2B files from familiar M2TS source material with known audio content
- Stripping the high-definition video from an M2TS file to produce a lightweight audio-only file for analysis or sampling in retro game audio workflows
Frequently Asked Questions
Not fully — this conversion involves a lossy transcode. M2TS files often carry high-quality audio such as AAC, AC-3, or even lossless TrueHD or DTS-HD MA. All of these will be decoded and re-encoded into MP3 at 128k bitrate by the LAME encoder, which introduces compression artifacts. If your source audio is already lossy, this generation-loss compounds. For the best possible result within the J2B format's constraints, consider increasing the bitrate to 256k or 320k if audio fidelity matters.
J2B is the proprietary audio format used by Jazz Jackrabbit 2, developed by Epic Games in 1998. It wraps audio data in the ASYLUM Music Format with a simple custom header, and the game engine was built specifically to decode MP3 streams via the LAME codec architecture. It was never designed as a general-purpose audio container, so it has no support for modern codecs like AAC, Opus, or FLAC — only libmp3lame-compatible MP3 output is valid.
By default, FFmpeg selects the first audio stream it finds in the M2TS container. M2TS files from Blu-ray sources often contain multiple audio tracks — for example, a primary TrueHD 7.1 track and a secondary AC-3 compatibility track. If you need a specific track other than the first, you can modify the FFmpeg command by adding -map 0:a:1 (for the second audio track, zero-indexed) before the output filename. The browser tool processes the default stream, but the displayed FFmpeg command can be customized locally for multi-track selection.
The -b:a flag controls the MP3 bitrate for the J2B output. In the default command, it is set to 128k, which is a reasonable middle ground. You can replace 128k with 64k for a smaller file with lower quality, or increase it to 192k, 256k, or 320k for higher fidelity — all are valid options for libmp3lame. For example: ffmpeg -i input.m2ts -vn -c:a libmp3lame -b:a 256k output.j2b. Note that J2B files above 320k bitrate are not meaningful since that is MP3's maximum supported bitrate.
Yes, the displayed FFmpeg command is a single-file template that you can script for batch processing on your desktop. On Linux or macOS, you can use a shell loop: for f in *.m2ts; do ffmpeg -i "$f" -vn -c:a libmp3lame -b:a 128k "${f%.m2ts}.j2b"; done. On Windows, a similar for loop in Command Prompt or PowerShell achieves the same result. This is especially useful for large Blu-ray rip collections where files may exceed the browser tool's 1GB limit.
No. J2B is a minimalist format built around the ASYLUM Music Format header and has no support for metadata fields like track titles, artist names, language tags, or chapter markers. Any such metadata present in the M2TS source — including the audio language identifiers common in Blu-ray multi-track streams — will be silently discarded during the conversion. If metadata preservation is important, J2B is not a suitable target format; it is intended exclusively for use as a game audio asset container.
Technical Notes
M2TS wraps a Blu-ray BDAV or AVCHD MPEG-2 Transport Stream and can contain a wide variety of audio codecs including AAC, AC-3 (Dolby Digital), DTS, TrueHD, DTS-HD MA, and others depending on the source disc or camcorder. FFmpeg can decode all of these, but the J2B output format accepts only libmp3lame-encoded MP3 audio, meaning a full decode-and-reencode cycle is always required regardless of the source codec — there is no possibility of stream copying in this conversion. J2B files produced by this tool will play back in Jazz Jackrabbit 2's audio engine and compatible J2B players, but should not be expected to work in general-purpose media players since J2B is not a standard format. The conversion also drops all video streams, subtitle tracks, and chapter data that M2TS may carry, as J2B supports none of these features. Audio channel layouts beyond stereo (e.g., 5.1 or 7.1 surround from a Blu-ray source) will be handled by FFmpeg's default downmixing behavior when the MP3 encoder is invoked — libmp3lame outputs stereo MP3 by default. If you need to control the downmix explicitly, the -ac 2 flag can be added to the command before the output filename.