Convert M4V to VOC — Free Online Tool
Convert M4V video files to VOC audio format, extracting the audio stream and encoding it as raw PCM unsigned 8-bit audio — the native format of Creative Labs Sound Blaster cards. This tool strips the MPEG-4 container and AAC or MP3 audio, outputting a legacy-compatible VOC file ready for DOS-era applications and retro game modding.
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FFmpeg Command
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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
M4V files typically contain a video stream encoded in H.264 or H.265 alongside an AAC audio track, all wrapped in Apple's MPEG-4 container. During this conversion, the video stream is discarded entirely — VOC is an audio-only format with no support for video. The AAC audio from the M4V is decoded to raw PCM and then re-encoded as unsigned 8-bit PCM (pcm_u8), the default codec for VOC files. This re-encoding step does involve quality reduction, since AAC is a modern compressed format and pcm_u8 offers only 256 amplitude levels and typically a sample rate capped around 44.1kHz — sufficient for retro applications but noticeably less dynamic than the source. The resulting VOC file carries the raw audio data in Creative Labs' structured chunk format, which DOS game engines and Sound Blaster-era tools can read directly.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg tool, which handles the full pipeline of demuxing the M4V container, decoding the AAC audio stream, and re-encoding it as PCM for the VOC output. |
-i input.m4v
|
Specifies the input file — an M4V container, which is Apple's MPEG-4 variant typically holding H.264 or H.265 video and AAC audio. FFmpeg will read all streams but only the audio will be used in the output. |
-c:a pcm_u8
|
Sets the audio codec to unsigned 8-bit PCM, which is the native and most compatible codec for the VOC format. This decodes the source AAC audio and re-encodes it as raw 8-bit PCM data that Sound Blaster hardware and DOS applications expect. |
output.voc
|
Specifies the output filename with the .voc extension, which tells FFmpeg to use the VOC muxer. The resulting file will be a Creative Labs VOC-format audio file containing the extracted and re-encoded audio from the M4V source, with no video, metadata, or subtitle data. |
Common Use Cases
- Extracting a music track or sound effect from an iTunes M4V download to use as a custom sound in a DOS game or retro game mod that requires VOC-format audio assets
- Converting narration or dialogue recorded in M4V format into VOC files for playback in a DOSBox environment running classic multimedia software
- Preparing audio content from Apple video files for use with legacy Creative Labs tools like Sound Blaster Wave Studio or early CD-ROM game editors that only accept VOC input
- Archiving or restoring period-accurate audio assets for retro computing projects where the Sound Blaster VOC format is required for hardware or emulator compatibility
- Pulling voice-over audio from an M4V tutorial or presentation to convert into VOC format for embedding in a custom DOS-based interactive demo or slideshow application
- Sampling audio from iTunes-purchased M4V content to create 8-bit style sound bites for chiptune or demoscene projects that work within the VOC format's raw PCM constraints
Frequently Asked Questions
Yes, there is a noticeable quality reduction. AAC audio in M4V files is a modern lossy codec capable of high-fidelity sound at 128kbps or above, with 16-bit or higher bit depth. VOC's pcm_u8 codec uses only 8-bit unsigned PCM, which means just 256 discrete amplitude levels and a higher noise floor — you may hear a slight graininess or hiss compared to the source. For retro gaming and DOS-era applications, this quality level is entirely appropriate and matches original Sound Blaster content.
The video stream is completely discarded. VOC is a strictly audio-only format developed for the Sound Blaster card and has no mechanism to store video data, chapters, or subtitles. Only the first audio track from the M4V is extracted and converted. If your M4V contains multiple audio tracks, FFmpeg will select the default audio stream — typically the first one.
Yes, VOC supports signed 16-bit little-endian PCM (pcm_s16le), which provides 65,536 amplitude levels compared to pcm_u8's 256 — a substantial quality improvement. To use it, change the FFmpeg command to: ffmpeg -i input.m4v -c:a pcm_s16le output.voc. However, be aware that some older DOS applications and Sound Blaster hardware only support 8-bit VOC files, so pcm_s16le compatibility depends on your target application.
No. The VOC format has no support for metadata tags, chapter markers, or any of the rich metadata that M4V files can carry (such as iTunes artist, album, or track titles). All of this information is lost during conversion. VOC stores only raw audio data in a simple chunk-based structure with minimal header information — it was designed for real-time audio playback on DOS systems, not media organization.
You can specify the output sample rate by adding the -ar flag to the command. For example, to output at 22050 Hz — a common rate for DOS game audio — use: ffmpeg -i input.m4v -c:a pcm_u8 -ar 22050 output.voc. Many classic VOC files used 8000 Hz, 11025 Hz, or 22050 Hz sample rates. Using a lower sample rate reduces file size but further reduces audio fidelity, which may actually be desirable for period-accurate retro content.
Yes, on the command line you can use a shell loop to process multiple files. On Linux or macOS, use: for f in *.m4v; do ffmpeg -i "$f" -c:a pcm_u8 "${f%.m4v}.voc"; done. On Windows Command Prompt, use: for %f in (*.m4v) do ffmpeg -i "%f" -c:a pcm_u8 "%~nf.voc". This is especially useful for batch-converting a collection of M4V files for a retro game mod or DOSBox project, and is the recommended approach for large batches that exceed the browser tool's 1GB file limit.
Technical Notes
The VOC format was introduced by Creative Labs in 1989 alongside the Sound Blaster card and uses a chunk-based binary structure with a fixed 26-byte header. FFmpeg's VOC muxer supports two PCM codecs: pcm_u8 (8-bit unsigned, the historical default matching original Sound Blaster hardware) and pcm_s16le (16-bit signed little-endian, supported by later Sound Blaster 16 hardware). When converting from M4V, FFmpeg must fully decode the AAC audio before re-encoding to PCM — there is no possibility of stream copying since the source codec and container are entirely incompatible with VOC. M4V files may contain DRM-protected content (FairPlay); FFmpeg cannot process DRM-locked M4V files, and this tool will fail on such inputs — only DRM-free M4V files (such as those from iTunes purchases that have been unlocked, or M4V files created from non-DRM sources) will convert successfully. The M4V container's iTunes-specific features — multiple audio tracks, subtitle tracks, and chapter data — are all silently dropped, as VOC supports none of these. Output file sizes will be significantly larger than the source AAC audio despite the lower quality, because raw PCM is uncompressed: a 3-minute audio clip at 44.1kHz pcm_u8 will produce approximately 7.9MB, compared to a few hundred kilobytes for equivalent AAC content.