Convert MTS to J2B — Free Online Tool
Convert MTS camcorder footage from Sony or Panasonic cameras to J2B format by extracting the audio track and encoding it as MP3 using the LAME encoder. This niche conversion strips the H.264 video and AC-3/AAC audio from the AVCHD transport stream, producing a J2B-wrapped MP3 suitable for use with Jazz Jackrabbit 2 game audio tooling.
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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
MTS files are AVCHD recordings packaged in an MPEG-2 Transport Stream container, typically carrying H.264 video and AC-3 or AAC audio captured by Sony or Panasonic camcorders. Since J2B is a game-specific audio-only format used by Jazz Jackrabbit 2 — essentially a simple header wrapping the ASYLUM Music Format — the video stream is completely discarded during this conversion. FFmpeg demuxes the transport stream, extracts the audio track, and re-encodes it using the libmp3lame encoder at 128k bitrate, then writes the result with a .j2b extension. No video data is carried through, and J2B supports only a single audio track, so only the primary audio stream from the MTS file will be preserved.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg tool, which handles demuxing the MPEG-2 Transport Stream from the MTS file, decoding the audio, and re-encoding it for the J2B output. |
-i input.mts
|
Specifies the input AVCHD file in MTS format, as recorded by a Sony or Panasonic camcorder. FFmpeg will parse the MPEG-2 Transport Stream container to locate the H.264 video and AC-3 or AAC audio streams inside. |
-c:a libmp3lame
|
Instructs FFmpeg to encode the audio stream using the LAME MP3 encoder. J2B only supports MP3 audio, so this is a required step — the original AC-3 or AAC audio from the MTS file cannot be passed through directly and must be transcoded. |
-b:a 128k
|
Sets the MP3 audio bitrate to 128 kilobits per second. This is a moderate quality setting that balances file size against audio fidelity for typical camcorder-recorded speech and ambient sound; increase to 256k or 320k if the source audio has significant musical or tonal content. |
output.j2b
|
Defines the output filename with the .j2b extension, causing FFmpeg to write the encoded MP3 audio wrapped in the Jazz Jackrabbit 2 J2B container header. The video stream from the MTS source is automatically discarded because J2B is an audio-only format. |
Common Use Cases
- Extracting ambient sound or location audio recorded on a Sony or Panasonic camcorder to use as a custom music track in Jazz Jackrabbit 2 fan mods or level editors
- Converting field-recorded audio from AVCHD footage into a format compatible with legacy Jazz Jackrabbit 2 audio replacement tools that expect J2B-formatted files
- Stripping the audio from MTS camcorder clips to produce MP3-based J2B files for retro game audio experiments or demoscene projects
- Archiving or repurposing the audio layer of MTS recordings into a compact, single-track MP3 container for use in tools or pipelines that specifically ingest J2B
- Testing or debugging Jazz Jackrabbit 2 audio modding workflows by generating J2B files from real-world recorded audio rather than synthesized module music
Frequently Asked Questions
No — J2B is a strictly audio-only format and cannot store any video data. The entire H.264 video stream from the MTS file is discarded during conversion. Only the audio track is extracted, re-encoded as MP3 via libmp3lame, and written to the J2B file. If you need to retain the video, you should convert to a video-capable format like MP4 or MKV instead.
Because J2B supports only a single audio track, FFmpeg will select the default (usually the first) audio stream from the MTS transport stream. AVCHD recordings sometimes include secondary audio tracks or commentary channels. If you need a specific non-default track, you can modify the FFmpeg command to add '-map 0:a:1' (or the appropriate stream index) before the output filename to explicitly select a different audio stream.
Yes, there will be some quality loss. AC-3 audio in AVCHD is typically encoded at 192k to 448k bitrate, and the conversion re-encodes it as MP3 at 128k using libmp3lame — a lossy-to-lossy transcode. The re-encoding process introduces a second generation of compression artifacts on top of whatever was already introduced by the AC-3 encoding. If audio fidelity matters, you can increase the bitrate in the command by changing '-b:a 128k' to '-b:a 256k' or '-b:a 320k'.
No. While MTS/AVCHD can carry subtitle streams, J2B does not support subtitles or chapters at all. All non-audio data — video, subtitles, metadata — is silently dropped during the conversion. The J2B output contains only the re-encoded MP3 audio wrapped in the J2B header.
The audio bitrate is controlled by the '-b:a 128k' flag in the command. Replace '128k' with your desired bitrate — for example, '-b:a 256k' for better quality or '-b:a 64k' for a smaller file. For this conversion from camcorder audio to MP3, values between 192k and 320k will yield the most transparent results, while anything below 96k will introduce noticeable compression artifacts, particularly in voices and ambient room sound typical of camcorder recordings.
The displayed command processes one file at a time, but on a desktop system you can batch process using a shell loop. On Linux or macOS, run: 'for f in *.mts; do ffmpeg -i "$f" -c:a libmp3lame -b:a 128k "${f%.mts}.j2b"; done'. On Windows Command Prompt, use: 'for %f in (*.mts) do ffmpeg -i "%f" -c:a libmp3lame -b:a 128k "%~nf.j2b"'. Note that the in-browser tool processes one file per conversion due to WebAssembly memory constraints.
Technical Notes
The J2B format is historically tied to Jazz Jackrabbit 2 and is based on the ASYLUM Music Format (AMF) with a small proprietary header — it was never designed as a general-purpose audio container, and conventional media players will not recognize .j2b files. FFmpeg's ability to write this container is limited to wrapping MP3 audio encoded by libmp3lame; no other audio codec is supported for J2B output. The source MTS file's transport stream timestamps, program map tables, and AVCHD metadata (including GPS data, shooting mode, and camera model fields sometimes embedded by Sony and Panasonic devices) are all lost in the output — J2B has no metadata layer. Because this is a lossy re-encode from an already-lossy source (AC-3 or AAC in the AVCHD stream), the resulting audio quality is bounded by both the original recording bitrate and the target MP3 bitrate. For camcorder audio that was recorded at 48kHz, libmp3lame will downsample or resample as needed to conform to standard MP3 sample rates; 48kHz is supported by LAME so the sample rate is typically preserved. Users working with MTS files larger than 1GB should use the displayed FFmpeg command locally rather than the browser-based tool, as WebAssembly processing is memory-constrained.