Extract Audio from MKV to VOC — Free Online Tool
Extract audio from MKV video files and save it as a VOC file — the retro PCM audio format developed by Creative Labs for Sound Blaster hardware. The conversion decodes whatever audio codec is inside your MKV (AAC, MP3, Opus, FLAC, etc.) and re-encodes it as raw 8-bit unsigned PCM, the native format of classic DOS Sound Blaster cards.
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FFmpeg Command
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DownloadHow It Works
MKV is a modern container that can hold almost any audio codec — AAC, Opus, FLAC, Vorbis, and more. VOC, by contrast, is a rigid legacy format that only supports raw PCM audio data, specifically 8-bit unsigned (pcm_u8) or 16-bit signed little-endian (pcm_s16le) samples. This conversion strips the video stream entirely, then decodes the MKV's audio codec and re-encodes it as uncompressed 8-bit PCM wrapped in the VOC container structure. Because the source audio is almost certainly a compressed modern codec and the output is uncompressed raw PCM at a fixed 8-bit depth, this is a full transcode — not a remux — and the resulting file reflects the quality ceiling of 8-bit audio, which is noticeably lower fidelity than the source.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg binary — the open-source multimedia processing engine that handles all decoding, stream selection, re-encoding, and VOC container writing in this conversion. |
-i input.mkv
|
Specifies the input Matroska file. FFmpeg will parse the MKV container and detect all contained streams — video, audio (e.g., AAC or FLAC), subtitles, and chapter data — making them available for processing. |
-vn
|
Disables video output entirely. Since VOC is a pure audio format with no video support, this flag ensures the video stream from the MKV is ignored rather than causing an error or being included in the output. |
-c:a pcm_u8
|
Instructs FFmpeg to encode the audio as 8-bit unsigned PCM — the native sample format of the original Creative Labs Sound Blaster VOC specification. This fully decodes the MKV's source audio codec (e.g., AAC, Opus, FLAC) and re-encodes it at this reduced bit depth. |
output.voc
|
Sets the output filename with the .voc extension, which tells FFmpeg to use the VOC muxer and write a properly structured Sound Blaster VOC file containing the raw 8-bit PCM audio data. |
Common Use Cases
- Extracting audio from an MKV gameplay recording to create a sound effect sample for a retro DOS game mod or demoscene project
- Preparing voice lines or music cues stored in MKV format for playback on a vintage Sound Blaster-equipped DOS PC or emulator like DOSBox
- Converting documentary or archival MKV footage audio into VOC format for integration into a retro-style interactive multimedia CD-ROM project
- Extracting a specific audio track from an MKV file to produce a VOC sample compatible with old-school tracker or MOD music software that expects Sound Blaster assets
- Archiving or reproducing the audio assets of a classic game that originally shipped with VOC files, sourcing replacement content from modern MKV recordings
Frequently Asked Questions
Yes, almost certainly. The default VOC output uses pcm_u8, which is 8-bit unsigned PCM — a very low bit depth that produces roughly 48 dB of dynamic range and audible quantization noise compared to modern 16-bit or 24-bit audio. Even if your MKV contains lossless FLAC audio, the re-encoding to 8-bit PCM is a destructive step that cannot be undone. This quality ceiling is an inherent limitation of the VOC format's retro origins, not a flaw in the conversion process.
VOC files are natively understood by very few modern applications. DOSBox and DOSBox-X both support VOC playback as part of their Sound Blaster emulation. Some retro game engines, ScummVM, and audio archaeology tools also read VOC. Standard media players like VLC, Windows Media Player, or macOS QuickTime will typically not open VOC files without plugins. The format is essentially a legacy artifact designed for Sound Blaster ISA cards from the late 1980s and 1990s.
All of them are discarded. VOC is a bare-bones audio-only format with no support for subtitles, chapters, metadata tags, or multiple audio tracks. The FFmpeg command uses -vn to drop the video stream, and the VOC container itself has nowhere to store any of this supplementary data. If your MKV has multiple audio tracks, FFmpeg will select the default audio track (usually track 0) unless you specify otherwise.
You can target a specific audio stream using the -map flag. For example, to select the second audio track, modify the command to: ffmpeg -i input.mkv -map 0:a:1 -vn -c:a pcm_u8 output.voc. The index 0:a:1 means the second audio stream (zero-indexed) from the first input file. You can run ffmpeg -i input.mkv first to list all available streams and identify the one you want.
Yes. Changing -c:a pcm_u8 to -c:a pcm_s16le will produce 16-bit signed little-endian PCM, which offers a significantly higher dynamic range (around 96 dB) and much lower quantization noise. The modified command would be: ffmpeg -i input.mkv -vn -c:a pcm_s16le output.voc. Note that some legacy DOSBox configurations and very old Sound Blaster hardware only support 8-bit VOC natively, so check your target playback environment before switching.
On Linux or macOS, you can loop over files in a directory with: for f in *.mkv; do ffmpeg -i "$f" -vn -c:a pcm_u8 "${f%.mkv}.voc"; done. On Windows Command Prompt, use: for %f in (*.mkv) do ffmpeg -i "%f" -vn -c:a pcm_u8 "%~nf.voc". Each MKV file will be processed sequentially, producing a matching VOC file. The browser-based tool handles one file at a time, so the FFmpeg command is especially useful for bulk processing large collections.
Technical Notes
The VOC format was introduced by Creative Labs around 1989 and stores audio as raw PCM blocks with a simple header describing sample rate, bit depth, and channel count. It has no concept of metadata tags, embedded artwork, or multi-track audio — features MKV was explicitly designed to support. The default codec used here, pcm_u8, stores each sample as an unsigned 8-bit integer, meaning sample values range from 0 to 255 with 128 representing silence. This is the format that original Sound Blaster cards operated in natively. The sample rate of the output VOC will be inherited from the source MKV audio stream, but be aware that very high sample rates (e.g., 96 kHz) may not be compatible with all DOSBox configurations or vintage hardware, which typically expected 8000–44100 Hz. There is no audio quality parameter to tune for this conversion — the output fidelity is entirely determined by the bit depth (8-bit vs. 16-bit) and the sample rate of the source material. File size for VOC will generally be larger than a compressed MKV audio track (since PCM is uncompressed) but smaller than a 16-bit WAV of the same duration, owing to the reduced bit depth.