Convert HEVC to J2B — Free Online Tool
Convert HEVC video files to J2B audio format, extracting and encoding the audio stream as MP3 using the libmp3lame codec at 128k bitrate. This niche conversion is aimed at Jazz Jackrabbit 2 modders and game audio enthusiasts who need to produce J2B-compatible audio from modern video sources.
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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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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) is a video-only or video-with-audio container/codec pairing — the input file may carry an audio stream alongside its highly compressed H.265 video. During this conversion, FFmpeg discards the HEVC video stream entirely and targets only the audio, re-encoding it using the libmp3lame encoder into MP3 format at 128k bitrate. The resulting audio data is then wrapped in the J2B container, which is the ASYLUM Music Format with a simple proprietary header used by the Jazz Jackrabbit 2 game engine. No video data is preserved in the output — J2B is a purely audio format.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg tool, the open-source multimedia processing engine running here via WebAssembly (FFmpeg.wasm) in your browser, or natively on your desktop machine. |
-i input.hevc
|
Specifies the input file — an HEVC/H.265 encoded video file. FFmpeg will probe this file to identify all available streams, including the audio track that will be extracted and re-encoded for the J2B output. |
-c:a libmp3lame
|
Selects the libmp3lame encoder for the audio stream, producing MP3-encoded audio. MP3 is the audio format that the J2B container wraps, making this encoder the correct and necessary choice for JJ2-compatible output. |
-b:a 128k
|
Sets the MP3 audio bitrate to 128 kilobits per second. This is the default quality level for J2B output — adequate for in-game music use, though you can increase this to 192k or 320k in the command for higher fidelity at the cost of a larger file. |
output.j2b
|
Defines the output filename and triggers FFmpeg to wrap the encoded MP3 audio in a J2B container, the format used by Jazz Jackrabbit 2 for its music assets. The .j2b extension tells FFmpeg which container format to write. |
Common Use Cases
- A Jazz Jackrabbit 2 modder has recorded or downloaded a gameplay video in HEVC format and wants to extract its soundtrack or sound design as a J2B file for use as a custom level music track.
- A game developer creating JJ2 custom episodes wants to repurpose audio from an HEVC-encoded cinematic or cutscene into a J2B music file compatible with the game engine.
- A retro gaming community contributor is archiving or remastering JJ2 levels and needs to convert modern HEVC tutorial or showcase videos into J2B audio assets for redistribution.
- A content creator has captured HEVC screen recordings of JJ2 gameplay sessions and wants to strip the audio for use as looping background music in other J2B-compatible contexts.
- A fan project team is producing new JJ2 episode content and needs to convert composer-supplied HEVC video previews (with embedded audio tracks) into J2B files for in-game playback.
Frequently Asked Questions
No — J2B is a purely audio format derived from the ASYLUM Music Format and has no capacity to store video data. FFmpeg automatically drops the HEVC video stream and only processes the audio track from your input file. If your HEVC file has no audio stream at all, the conversion will produce an empty or invalid J2B file.
128k bitrate MP3 is the default and is generally sufficient for the in-game audio quality expected from JJ2, which was originally designed around late-1990s module music formats with modest fidelity. For higher quality output, you can modify the FFmpeg command to use -b:a 192k or -b:a 320k, though any improvement may be imperceptible within the game's audio pipeline. Keep in mind that any encoding step from the original HEVC source audio is lossy and irreversible.
Replace the value after -b:a in the command with your desired bitrate. For example, to encode at 320k, use: ffmpeg -i input.hevc -c:a libmp3lame -b:a 320k output.j2b. Supported options include 64k, 128k, 192k, 256k, and 320k — higher values produce larger files with better audio fidelity, while lower values save space at the cost of quality.
Yes, on desktop you can use a shell loop to process multiple files. On Linux or macOS, run: for f in *.hevc; do ffmpeg -i "$f" -c:a libmp3lame -b:a 128k "${f%.hevc}.j2b"; done. On Windows Command Prompt, use: for %f in (*.hevc) do ffmpeg -i "%f" -c:a libmp3lame -b:a 128k "%~nf.j2b". The in-browser tool processes one file at a time, so the command-line approach is recommended for batch workflows.
J2B is a minimal format based on the ASYLUM Music Format and does not support standard audio metadata tags the way formats like MP3 or OGG do natively. Any title, artist, or other metadata embedded in your HEVC source file will be lost during conversion. The J2B header is a simple wrapper and is not designed for metadata-rich use cases.
FFmpeg uses the output file extension to determine the container format and writes the encoded MP3 audio stream into a file with the .j2b extension. Since J2B wraps ASYLUM-format or MP3 audio with a basic header, this approach can produce a file that JJ2-compatible tools and the game engine recognize. The core audio codec doing the work is libmp3lame — the J2B container itself adds minimal overhead around that encoded audio data.
Technical Notes
The HEVC input format is a demanding video codec built for compression efficiency, but its audio streams are typically carried in standard codecs like AAC, AC3, or PCM — none of which are natively compatible with J2B. FFmpeg's libmp3lame encoder handles the transcode to MP3, which forms the audio payload inside the J2B wrapper. Because both the source audio (likely AAC or similar) and the output MP3 are lossy formats, this conversion involves a generation loss: audio is decoded from its original lossy format and re-encoded into MP3, which introduces additional compression artifacts. For best results, use the highest available source quality and consider bumping the bitrate to 192k or above. J2B files do not support multiple audio tracks, subtitles, chapters, or transparency, and neither does HEVC audio extraction in this pipeline — only the first detected audio stream will be processed. Files with HDR video metadata or 4K/8K resolution in the HEVC source are irrelevant to the output since all video data is discarded.