Extract Audio from MP4 to VOC — Free Online Tool
Extract audio from an MP4 video file and save it as a VOC file — the classic Sound Blaster audio format used in DOS-era games and multimedia. This tool decodes the MP4's AAC or MP3 audio stream and re-encodes it to raw unsigned 8-bit PCM (pcm_u8), the native codec of the VOC container.
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Estimated output:
Conversion Complete!
DownloadHow It Works
MP4 files typically carry compressed audio encoded in AAC, MP3, or Opus. The VOC format, developed by Creative Labs for Sound Blaster cards, stores raw uncompressed PCM audio — specifically unsigned 8-bit or signed 16-bit little-endian samples. This conversion fully decodes the compressed audio stream from the MP4 and re-encodes it as unsigned 8-bit PCM (pcm_u8) inside a VOC container. The video stream is discarded entirely. Because pcm_u8 is 8-bit audio, the resulting file will have reduced dynamic range compared to the original compressed audio — 8-bit PCM provides 48dB of dynamic range versus the effectively much higher fidelity of AAC. The VOC container also does not support metadata, chapters, or multiple audio tracks, so only the first audio stream is extracted and all metadata is dropped.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg multimedia processing tool. In the browser-based version of this tool, FFmpeg runs locally via WebAssembly (FFmpeg.wasm) — your MP4 file never leaves your device. |
-i input.mp4
|
Specifies the input file, an MP4 container that typically holds a video stream alongside a compressed audio stream encoded in AAC, MP3, or Opus. |
-vn
|
Disables video output entirely, discarding the video stream from the MP4. Since VOC is a purely audio-only format with no video support, this flag ensures only the audio stream is processed. |
-c:a pcm_u8
|
Decodes the MP4's compressed audio stream (typically AAC) and re-encodes it as unsigned 8-bit PCM — the native, most broadly compatible audio codec for the VOC format, matching what original Creative Labs Sound Blaster hardware and DOS software expect. |
output.voc
|
The output filename with the .voc extension, which tells FFmpeg to use its VOC muxer to write the file in the Creative Labs VOC binary container format, complete with the required VOC file header and data block structure. |
Common Use Cases
- Replacing or modding audio assets in classic DOS games that load sound effects from VOC files at runtime
- Creating authentic Sound Blaster-compatible audio files for retro computing projects or vintage hardware such as actual ISA Sound Blaster cards
- Supplying audio samples to DOS-era game engines or emulators like DOSBox that load VOC files for sound playback
- Preparing voice-acted dialogue or sound effects recorded as modern MP4 screencaptures for use in retro game development toolchains
- Archiving or converting MP4-encoded oral history recordings into VOC format for retro software preservation projects
- Extracting a speech or music track from an MP4 tutorial video to use as an in-game audio cue in a DOS homebrew game
Frequently Asked Questions
Yes, noticeably. The pcm_u8 codec stores audio as unsigned 8-bit PCM, which yields only 256 discrete amplitude levels and roughly 48dB of dynamic range. Your MP4 likely contains AAC audio, which despite being lossy delivers much higher perceived fidelity. The conversion to pcm_u8 will introduce audible quantization noise, reduced dynamic range, and a characteristically 'crunchy' lo-fi sound. This is inherent to the VOC format's 8-bit design and is expected for its intended retro/DOS use case.
Yes. VOC files also support signed 16-bit little-endian PCM (pcm_s16le), which provides 65,536 amplitude levels and roughly 96dB of dynamic range — a significant improvement over 8-bit. To use it, change the FFmpeg command to: ffmpeg -i input.mp4 -vn -c:a pcm_s16le output.voc. However, note that not all retro software, DOS games, or older Sound Blaster hardware supports 16-bit VOC files equally well; 8-bit VOC has broader compatibility with original DOS-era programs.
By default, FFmpeg will attempt to use the same sample rate as the source audio stream. However, VOC files and Sound Blaster hardware often expect specific sample rates such as 8000Hz, 11025Hz, 22050Hz, or 44100Hz. If your MP4 audio is at an unusual sample rate, you can force a standard one by adding -ar 22050 (or another target rate) to the command, for example: ffmpeg -i input.mp4 -vn -ar 22050 -c:a pcm_u8 output.voc. Matching the sample rate to what your target DOS software expects is important for correct playback speed.
No. The VOC format does not support metadata of any kind — no title, artist, album, or chapter markers. All such information from the MP4 is silently discarded during conversion. Additionally, if your MP4 contains multiple audio tracks (e.g., multiple language dubs), only the first audio stream is extracted by default. The VOC format is a simple binary audio container with no provision for rich metadata.
On Linux or macOS, you can use a shell loop: for f in *.mp4; do ffmpeg -i "$f" -vn -c:a pcm_u8 "${f%.mp4}.voc"; done. On Windows Command Prompt, use: for %f in (*.mp4) do ffmpeg -i "%f" -vn -c:a pcm_u8 "%~nf.voc". This processes every MP4 in the current directory and saves a corresponding VOC file with the same base filename. Batch processing is particularly useful when replacing multiple sound assets in a DOS game mod.
AAC audio in an MP4 is heavily compressed — a typical 128kbps AAC stream uses data very efficiently. PCM audio in a VOC file is completely uncompressed: every audio sample is stored as a raw byte. Even at 8-bit depth, a mono 22050Hz VOC file consumes about 22KB per second. Stereo or higher sample rates increase this proportionally. So while the audio quality is lower due to 8-bit resolution, the raw uncompressed storage means VOC files are often far larger per second of audio than the original AAC-encoded MP4 audio stream.
Technical Notes
The VOC format is a binary container defined by Creative Labs in the early 1990s, structured as a header block followed by typed data blocks carrying raw PCM samples. FFmpeg's VOC muxer supports pcm_u8 (unsigned 8-bit, the most historically common) and pcm_s16le (signed 16-bit little-endian). The default used here is pcm_u8, matching the widest DOS-era compatibility. Stereo audio is supported in VOC, but many original Sound Blaster cards and DOS game engines expect mono audio — if needed, add -ac 1 to the command to downmix to mono. There is no audio quality parameter for this conversion: since the output is uncompressed PCM, there is no bitrate knob to turn, only sample rate (-ar) and bit depth (choice of codec) to consider. One important limitation: the VOC format's sample rate is encoded as a single-byte divisor in some older VOC versions, which can cause compatibility issues for sample rates above 23kHz in strictly legacy-compliant implementations. FFmpeg writes a modern VOC header that avoids this in most cases, but testing playback in your target environment (DOSBox, actual hardware, etc.) is recommended.