Extract Audio from M4V to CAF — Free Online Tool
Extract audio from M4V video files and save it as CAF (Core Audio Format), Apple's professional-grade audio container. This tool strips the video stream entirely and outputs uncompressed PCM audio in a CAF file — ideal for high-fidelity audio archiving within the Apple ecosystem.
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FFmpeg Command
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Settings
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 carry AAC audio alongside H.264 or H.265 video. This tool discards the video stream entirely and re-encodes the audio as 16-bit signed little-endian PCM (pcm_s16le) inside a CAF container. Unlike simply remuxing the existing AAC stream, the conversion to PCM means the audio is decoded from its compressed AAC state and written as uncompressed waveform data — resulting in a lossless representation of what was encoded in the original file. CAF was designed by Apple specifically to overcome the 4GB file size limit of AIFF and WAV, making it a robust choice for storing large or long-duration audio tracks extracted from video.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg tool — in this browser-based tool, it runs as a WebAssembly binary (FFmpeg.wasm) entirely within your browser with no server involvement. On your desktop, this calls your locally installed FFmpeg executable. |
-i input.m4v
|
Specifies the input M4V file. FFmpeg reads the container and identifies all streams inside — typically an H.264 or H.265 video stream and an AAC audio stream, plus any subtitle or chapter tracks the M4V may contain. |
-vn
|
Disables video output entirely, telling FFmpeg to ignore the H.264 or H.265 video stream from the M4V. Without this flag, FFmpeg would attempt to include video in the output, which CAF cannot contain since it is a pure audio container. |
-c:a pcm_s16le
|
Sets the audio codec to signed 16-bit little-endian PCM, decoding the AAC audio from the M4V and writing it as uncompressed waveform data in the CAF file. This is the standard uncompressed format for Core Audio on Apple platforms and requires no decompression at playback time. |
-b:a 128k
|
Specifies a target audio bitrate of 128 kbps. For PCM codecs like pcm_s16le, FFmpeg ignores this value because the bitrate of uncompressed audio is fixed by sample rate and bit depth — it is included here as a parameter placeholder but has no effect on the output. |
output.caf
|
Defines the output filename and tells FFmpeg to write a CAF container. FFmpeg infers the CAF format from the .caf file extension and wraps the decoded PCM audio stream in Apple's Core Audio Format container structure. |
Common Use Cases
- Extracting the audio track from an iTunes-purchased M4V movie or TV episode to use as a high-quality source for audio editing in Logic Pro or GarageBand, both of which natively support CAF files.
- Archiving the audio commentary track from an M4V video in an uncompressed CAF file for long-term storage without further generational quality loss from re-compression.
- Pulling dialogue or narration audio from an M4V screencast or lecture recording into CAF format for use as stems in an Apple-ecosystem post-production workflow.
- Extracting music or a soundtrack from an M4V video file into CAF for use as a source asset in an Xcode project or iOS app that uses Core Audio APIs.
- Converting M4V audio to uncompressed PCM CAF as an intermediate step before applying processing in Audio Unit plugins that require uncompressed input.
- Stripping the audio from a large M4V file (potentially over 4GB in duration) into CAF, which — unlike WAV or AIFF — has no file size ceiling, making it safe for very long recordings.
Frequently Asked Questions
The original M4V file almost certainly contains AAC audio, which is already a lossy-compressed format. Converting that AAC audio to uncompressed PCM (pcm_s16le) in CAF does not recover any detail lost during the original AAC encoding, but it does not introduce any additional quality degradation either. What you get in the CAF file is a mathematically exact, uncompressed representation of the decoded AAC audio — no more, no less. Think of it as thawing out the compressed audio into its raw waveform form.
This tool uses pcm_s16le as the default output codec because CAF's primary strength is as a container for uncompressed, high-resolution audio in professional Apple workflows. While CAF does support AAC, simply remuxing AAC into CAF would produce a file with limited interoperability compared to the standard AIFF or M4A formats most apps expect for compressed audio. The PCM output is universally readable by every Core Audio-based application on macOS and iOS. If you need AAC specifically, the FFmpeg command shown can be adapted by replacing pcm_s16le with aac.
CAF does not support subtitles, chapters, or multiple audio tracks — it is a single-stream audio container. This tool extracts only the first audio track from the M4V file; any additional audio tracks, embedded subtitles, and chapter markers are discarded. If your M4V contains multiple audio tracks (e.g., a director's commentary alongside the main mix), you would need to run separate FFmpeg commands using the -map flag to target each track individually.
Significantly larger in most cases. AAC audio in M4V is compressed, typically at 128–256 kbps, while uncompressed PCM at 16-bit stereo 44.1 kHz runs at approximately 1.4 Mbps — roughly 5 to 10 times larger than the audio-only portion of the source file. A one-hour M4V whose audio track occupied around 56MB at 128k AAC would produce a CAF file of roughly 600MB. This is the tradeoff for having fully uncompressed audio.
The command uses -c:a pcm_s16le for uncompressed 16-bit audio, and the -b:a 128k flag is effectively ignored by FFmpeg for PCM codecs since bitrate is determined by sample rate and bit depth, not a compression target. To use a compressed codec instead, replace pcm_s16le with aac and set -b:a to your desired bitrate (e.g., 256k). For 24-bit uncompressed audio, replace pcm_s16le with pcm_s24le. To use FLAC (lossless compressed), replace it with flac and remove the -b:a flag entirely, since FLAC is lossless and bitrate-targeting does not apply.
Yes. On macOS or Linux, you can wrap the command in a shell loop: for f in *.m4v; do ffmpeg -i "$f" -vn -c:a pcm_s16le "${f%.m4v}.caf"; done. This iterates over every M4V in the current directory and produces a matching CAF file. On Windows Command Prompt, use: for %f in (*.m4v) do ffmpeg -i "%f" -vn -c:a pcm_s16le "%~nf.caf". The -b:a flag can be omitted for PCM output since it has no effect on uncompressed codecs.
Technical Notes
CAF (Core Audio Format) was introduced by Apple to serve professional audio use cases where AIFF and WAV fall short — specifically their 4GB file size limit imposed by 32-bit chunk size headers. CAF uses 64-bit chunk sizes, meaning a single CAF file can store theoretically unlimited audio data, which is relevant when extracting audio from very long M4V recordings. The default codec used here, pcm_s16le (signed 16-bit little-endian PCM), matches CD-quality resolution and is directly compatible with Core Audio on macOS and iOS without any decoding overhead. M4V files may carry DRM (FairPlay) protection on iTunes Store purchases; FFmpeg cannot process DRM-protected M4V files and will return an error — this applies equally to desktop use of the command. Non-DRM M4V files, such as those encoded locally or downloaded without protection, process normally. Metadata such as title, artist, and album tags embedded in the M4V are not automatically carried over to CAF, as CAF uses a different metadata chunk structure (CAF Info Strings) that FFmpeg does not populate from M4V atoms during this conversion.