Extract Audio from HEVC to J2B — Free Online Tool
Extract audio from HEVC/H.265 video files and save it as J2B, the ASYLUM Music Format-based audio container used by Jazz Jackrabbit 2. The conversion uses the LAME MP3 encoder to produce a 128k bitrate audio stream wrapped in the J2B container, stripping all video data entirely.
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FFmpeg Command
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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
HEVC (H.265) video files contain one or more audio streams alongside the compressed video. This tool discards the video stream entirely using the -vn flag and passes the audio through the libmp3lame encoder, transcoding it to MP3 at 128k bitrate. The resulting MP3-encoded audio is then written into a J2B container — a format originating from the Jazz Jackrabbit 2 game engine, which wraps ASYLUM Music Format data (typically MOD-style module music) but in this pipeline accepts the MP3 stream as its audio payload. Because both the source audio and the output are lossy, there will be a generation loss if the HEVC file's audio was itself already MP3; the original audio codec (commonly AAC or AC3 in H.265 files) is fully decoded and re-encoded to MP3 during this process.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg program, the open-source multimedia processing engine that powers this conversion both in the browser (via FFmpeg.wasm) and on the desktop command line. |
-i input.hevc
|
Specifies the input HEVC/H.265 video file. FFmpeg reads the container, detects the embedded video stream (encoded with libx265) and any audio streams present, and makes them available for processing. |
-vn
|
Disables video output entirely, ensuring the H.265 video stream from the HEVC file is discarded and only the audio track is written to the J2B output file. |
-c:a libmp3lame
|
Selects the LAME MP3 encoder to transcode the audio extracted from the HEVC file into MP3 format, which serves as the audio payload inside the J2B container. |
-b:a 128k
|
Sets the MP3 audio bitrate to 128 kilobits per second, the default quality level for this conversion. This is the standard mid-range MP3 bitrate; increase it to 192k or 320k in the command for higher fidelity output at the cost of a larger file. |
output.j2b
|
Defines the output filename and instructs FFmpeg to write the result into a J2B container — the Jazz Jackrabbit 2 audio format based on the ASYLUM Music Format — with the MP3-encoded audio stream as its content. |
Common Use Cases
- Extracting a music or ambient soundtrack from an H.265-encoded video to inject into a Jazz Jackrabbit 2 custom level that expects J2B audio files.
- Pulling the audio commentary track from a 4K HEVC screen recording or gameplay capture to repurpose as a standalone J2B music asset for retro game modding.
- Converting an HEVC-encoded cinematic or cutscene audio track into J2B format for use with Jazz Jackrabbit 2 fan-made episode packs.
- Stripping and re-encoding the audio from an H.265 video file to produce a compact 128k MP3-based J2B file for embedding in a JJ2 level editor without carrying any video overhead.
- Archiving a specific audio track from an HEVC source into J2B as part of a retro game modding workflow where J2B is the required delivery format for the game engine.
Frequently Asked Questions
Yes, there will be quality loss because the audio is transcoded to MP3 at 128k bitrate regardless of what codec was used in the original HEVC file. If the source HEVC file contained AAC or AC3 audio, those streams are fully decoded and then re-encoded as lossy MP3 — this generation loss is unavoidable. If maximum fidelity matters, you can increase the bitrate to 192k, 256k, or 320k using the -b:a flag in the FFmpeg command before the output filename.
The J2B format was designed specifically for ASYLUM Music Format module data used by the Jazz Jackrabbit 2 engine, and the game's native player expects that module structure. A J2B file built from an MP3 stream extracted from a video is technically non-standard and may not play correctly in the original game engine. However, community tools, custom JJ2 level editors, or modified game clients that handle J2B more loosely may accept the file. Test compatibility with your specific target environment before relying on the output.
The -vn flag explicitly disables video stream processing, ensuring that only the audio track from the HEVC file is written to the output. If you remove -vn, FFmpeg would attempt to include a video stream in the J2B output, which the J2B container does not support, likely resulting in an error or a malformed file. Keeping -vn is essential for a clean audio-only extraction.
Replace the 128k value in the -b:a 128k portion of the command with your preferred bitrate. For example, use -b:a 320k for the highest standard MP3 quality, or -b:a 192k for a middle-ground option. The full modified command would look like: ffmpeg -i input.hevc -vn -c:a libmp3lame -b:a 320k output.j2b. Higher bitrates increase file size but reduce the audible artifacts introduced by MP3 compression.
No. HDR color metadata, 4K resolution data, and all video-layer information are completely ignored during this conversion because the -vn flag discards the video stream before any processing occurs. The audio extraction reads only the audio track embedded in the HEVC container, so whether the source is an 8K HDR file or a standard 1080p clip makes no difference to the output J2B file.
Yes, on the command line you can use a shell loop to process multiple files. On Linux or macOS, run: for f in *.hevc; do ffmpeg -i "$f" -vn -c:a libmp3lame -b:a 128k "${f%.hevc}.j2b"; done. On Windows Command Prompt, use: for %f in (*.hevc) do ffmpeg -i "%f" -vn -c:a libmp3lame -b:a 128k "%~nf.j2b". The browser-based tool on this page processes one file at a time, so the desktop FFmpeg command is the practical choice for batch workflows.
Technical Notes
HEVC (H.265) containers commonly carry audio encoded as AAC, AC3, DTS, or occasionally MP3, depending on the source. This tool decodes whichever audio codec is present and re-encodes it to MP3 using libmp3lame at 128k CBR — a constant bitrate mode that produces predictable file sizes but does not adapt to the complexity of the audio signal the way VBR would. The J2B format is a niche container rooted in the Jazz Jackrabbit 2 game engine, originally designed to hold ASYLUM Music Format tracker module data rather than conventional PCM-derived compressed audio. Using it as a wrapper for an MP3 stream extracted from a video source is an unconventional application; the container header will be written but the semantic compatibility with JJ2-native tooling is not guaranteed. Metadata such as chapter markers, subtitle tracks, and secondary audio tracks present in the HEVC source are all dropped, as J2B supports none of these features. If the HEVC source has multiple audio tracks, FFmpeg will default to the first detected audio stream; to select a specific track, add -map 0:a:1 (or the relevant index) before the output filename in the command.