What is the FSB file format?
.FSB is an FMOD Sample Bank, a proprietary binary audio container developed by Firelight Technologies for use with the FMOD audio engine. It packages one or more audio samples into a single file optimized for real-time loading and streaming in games and interactive applications.
The format has evolved through several versions: FSB3 and FSB4 were used with the now-discontinued FMOD Designer tool, while FSB5 is the current format used by FMOD Studio and FMOD Engine 2.x. Each .fsb file begins with a 4-byte ASCII magic identifier (FSB3, FSB4, or FSB5). Audio codecs are stored per-sample in the header and can vary across samples within the same bank - options include PCM, IMA ADPCM, MP3, Ogg Vorbis, FADPCM, Opus, AT9 (PlayStation), and XMA (Xbox).
.fsb files are widely used in Unity-based games: Unity 5 and later packages audio as FSB5 banks embedded in .assets bundles. Unity projects can optionally encrypt FSB5 banks using AES-128, which prevents extraction without the project key.
Community tools such as vgmstream (available as a foobar2000 plug-in or standalone CLI) can decode most unencrypted .fsb files. The python-fsb5 library supports FSB5 extraction programmatically.
Security & safety
RISK: LOWFSB files are audio data containers; they cannot execute code. No malware vector is known for .fsb. However, some game publishers restrict audio extraction from their FSB banks for copyright reasons - check the game's EULA before distributing extracted audio.
Format details
in a nutshellPrograms that open FSB files
Windows6 apps
vgmstream (foobar2000 plug-in)
Open-source Install the vgmstream foobar2000 component; drag the .fsb into foobar2000 to play individual samples or batch-decode to WAV.
vgmstream (CLI)
Open-source Run 'vgmstream-cli -o output.wav input.fsb' to extract all samples. Use '-S 0' to specify a subsong index.
python-fsb5
Open-source Python CLI: 'python extract.py input.fsb' - extracts samples from FSB5 files to WAV/OGG. Requires Python 3.
Fmod5Sharp
Open-source C# library for decoding FSB5; used programmatically or via Unity asset extractor tools (AssetRipper).
FSB Extractor (AEZAY)
Free GUI tool for extracting audio from FSB3/FSB4 files; limited FSB5 support.
FMOD Studio
Freemium Official FMOD authoring tool; can open and play FSB banks within a FMOD Studio project context. 
macOS2 apps
vgmstream (CLI)
Open-source Same as Windows CLI; macOS build available via Homebrew or GitHub releases. 
Linux1 app
Technical details
deep spec| Container format | Proprietary Firelight FSB binary container (not ZIP, not RIFF) |
| Magic bytes | 46 53 42 35 = "FSB5" (current); FSB3 = 46 53 42 33, FSB4 = 46 53 42 34 |
| Byte order | Little-endian |
| Format versions | FSB1, FSB2, FSB3, FSB3.1, FSB4, FSB5; FSB5 is current (FMOD Studio / FMOD Engine 2.x) |
| Supported audio codecs (per sample) | PCM, IMA ADPCM, MP3, Ogg Vorbis, FADPCM, Opus, AT9 (PS4/PS5), XMA (Xbox) |
| Encryption | Optional AES-128 (FSB5); Unity encrypts banks by default - extraction requires the project key |
| Typical file size | 500 KB - 500 MB (varies widely by game and sample count) |
| Supported sample rates | 8,000-192,000 Hz per sample; game audio typically 22,050-48,000 Hz |
| Per-sample codec flexibility | Yes - different samples in the same bank can use different codecs and sample rates |
| Platform support | Windows, macOS, Linux, PlayStation, Xbox, Nintendo Switch, Android, iOS |
| Unity integration | Unity 5+ embeds audio as FSB5 banks in .assets bundles; produced automatically by the Unity Editor |
| Integrity verification | None in the FSB format itself; Unity verifies via asset bundle hash externally |
| Runtime role | Runtime audio bank loaded by FMOD Engine at play time; FMOD Studio .bank files are used at authoring level |
| Released | Late 1990s (FMOD API); FSB3 widely used from ~2002; FSB5 from FMOD Studio 1.x (~2013) |
| Latest version | FSB5 (FMOD Studio / FMOD Engine 2.x, current) |
| Specification | www.fmod.com |
FSB conversions
Community Q&A
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