What is the SFK file format?
.sfk is a temporary cache file generated automatically by Sound Forge, VEGAS Pro, and ACID Pro - software originally developed by Sonic Foundry and later owned by Sony, then MAGIX. The .sfk file stores precomputed graphical peak data that visually represents a .wav audio waveform, enabling the host application to redraw the audio timeline instantly without re-reading the full audio on every load. .sfk files do not contain any actual audio samples; the audio itself remains in the paired .wav or other supported media file.
.sfk files only represent WAV file data and do not contain any actual audio data - such data is stored in the related media file. Because an .sfk is purely a display cache, it cannot be meaningfully opened or edited manually; a hex editor can inspect its binary contents, but no dedicated viewer exists for the proprietary format.
An .sfk file is generated automatically when a media file is opened in any of the supported applications. The .sfk file is saved in the same folder and under the same base filename as the related media file - for example, recording.wav generates recording.sfk. If .sfk files have not been automatically removed upon closing the program, they can be deleted manually without any loss of audio data.
Deleting an .sfk is safe; the application will regenerate it the next time the media file is opened. Related peak-cache formats serving the same role on other platforms include .sfl (the older Sound Forge format), .pkf (Pro Tools), and .asd (Ableton Live).
Security & safety
RISK: LOWSFK is a harmless, disposable cache file - it holds only waveform-drawing data, no executable code and no audio. It is safe to delete: Sound Forge/VEGAS simply regenerate it the next time you open the matching audio file. The only thing to avoid is third-party 'SFK player/converter' downloads from ad portals - there is nothing inside an .sfk to play or convert, so such tools are at best useless and often PUP/adware. The real audio is always in the neighbouring source file.
Format details
in a nutshellPrograms that open SFK files
Windows3 apps
MAGIX/Sony Sound Forge (Pro)
Paid You don't open the .sfk directly - open the matching audio file (e.g. song.wav) in Sound Forge; it uses the .sfk to draw the waveform and regenerates it if missing.
MAGIX/Sony VEGAS Pro
Paid Same as Sound Forge: VEGAS Pro creates/uses .sfk peak files for its timeline audio; open the audio/project, not the .sfk.
Hex editor (e.g. HxD)
Free Only to confirm what it is - an .sfk has no playable audio. Use this just to inspect; there is nothing to extract. Technical details
deep spec| Format type | Binary waveform peak cache - stores precomputed min/max amplitude data, not audio samples |
| Naming convention | Shares the base filename of its paired media file; recording.wav produces recording.sfk in the same directory |
| Platform | Windows (Sound Forge, VEGAS Pro, and ACID Pro are Windows-only applications) |
| MIME type | application/octet-stream - no dedicated MIME type is registered for this format |
| Binary structure | Proprietary binary with an undocumented Sound Forge peak header; no published specification exists |
| Data content | Min/max amplitude values (peaks) per time segment at multiple resolutions, enabling fast waveform rendering at any zoom level |
| Auto-generation | Created automatically the first time a supported audio file is opened in Sound Forge, VEGAS Pro, or ACID Pro |
| Deletability | Safe to delete - no audio data is stored; the host application regenerates the file on the next open |
| Predecessor format | .sfl - the older Sound Forge peak format that .sfk replaced in later versions of the software |
| Related peak formats | .pkf (Pro Tools), .asd (Ableton Live), .ovw (Adobe Audition) serve the same waveform-cache role in other DAWs |
| Developer lineage | Sonic Foundry (1990s) → Sony Creative Software → MAGIX (2016 acquisition) → Boris FX (Sound Forge Pro) |
| File size | Much smaller than the paired audio file; contains only statistical peak data, not audio samples |
| Orphaned files | Left behind when a media file is moved or the application crashes; safe to delete without consequence |
| Rendering purpose | Eliminates the need to decode the full audio on every session open, making waveform display near-instantaneous |
| Released | 1990s (Sonic Foundry Sound Forge); replaced the older .sfl peak format |
SFK conversions
Community Q&A
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