Extract Audio from CAVS to M4A — Free Online Tool
Extract the AAC audio track from a CAVS video file and save it as an M4A file — Apple's MPEG-4 audio container optimized for iTunes, iPhone, and web playback. Because CAVS natively encodes audio as AAC, the audio stream is copied directly without re-encoding, preserving the original quality instantly.
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FFmpeg Command
Copy this command to run the same conversion locally with FFmpeg on your desktop. Download FFmpeg
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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
CAVS (Chinese Audio Video Standard) files carry their audio as AAC, which is also the native codec for the M4A container. This means the conversion is primarily a remux operation for the audio stream: FFmpeg strips out the video entirely using the -vn flag, then lifts the AAC audio data and repackages it inside an MPEG-4 (.m4a) wrapper without decoding and re-encoding the audio. The result is a lossless copy of the original audio quality at near-instant speed. The only active encoding step is if you change the default bitrate, in which case the AAC stream is re-encoded at your chosen target. The output M4A file is fully compatible with Apple devices, iTunes metadata tagging, gapless playback, and HTML5 web audio players.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg multimedia processing engine, which runs here as a WebAssembly module entirely inside your browser — no server receives your CAVS file at any point. |
-i input.cavs
|
Specifies the input file in CAVS format. FFmpeg reads the container, identifies the H.264 video stream and the AAC audio stream inside it, and prepares to process them according to the output options. |
-vn
|
Disables video output entirely, ensuring the M4A file contains only the audio track. Since M4A is an audio-only container and CAVS's video uses H.264 which has no place in an M4A file, this flag is essential to produce a valid output. |
-c:a aac
|
Sets the audio codec to AAC. Because the CAVS source already contains AAC audio and the output M4A container uses AAC natively, this setting enables a direct stream copy pathway, preserving the original audio without re-encoding when the bitrate is unchanged. |
-b:a 128k
|
Sets the audio bitrate to 128 kilobits per second. This matches the default quality setting and is suitable for broadcast speech and general audio; if the original CAVS audio bitrate differs, FFmpeg will re-encode the AAC stream at this target rather than copying it. |
-vn
|
A second instance of the video-disable flag, which is redundant but harmless. The effective instruction to strip the video was already given by the first -vn; this duplicate has no additional impact on the output. |
output.m4a
|
Defines the output filename and signals FFmpeg to use the MPEG-4 audio container format. The .m4a extension ensures compatibility with Apple iTunes, iPhone, Safari, and any player that recognizes the standard MPEG-4 audio file type. |
Common Use Cases
- Extracting broadcast-quality audio from Chinese digital television recordings stored in CAVS format for archiving or editing in a DAW
- Pulling the soundtrack or dialogue from a CAVS-encoded video to create an M4A file that plays natively on iPhone, iPad, or Apple Music without any additional conversion
- Isolating narration or commentary from a CAVS broadcast clip to use as a podcast episode or audio-only asset on platforms like Apple Podcasts
- Reducing file size for distribution by discarding the CAVS video stream and delivering only the AAC audio track in a universally playable M4A container
- Preparing CAVS audio content for use in iOS or macOS apps that rely on the MPEG-4 audio format for AVFoundation playback compatibility
- Archiving the audio layer of CAVS-format media separately so it can be re-synced with re-encoded video later in a post-production workflow
Frequently Asked Questions
In most cases, no. Because CAVS files encode audio as AAC and M4A is also an AAC container, FFmpeg remuxes the audio stream directly without decoding or re-encoding it. The audio data is bit-for-bit identical to the original, so there is zero generation loss. Quality degradation would only occur if you explicitly change the bitrate setting, which forces a re-encode at the new target bitrate.
M4A is the logical choice here because both the source CAVS file and M4A use AAC audio, making a direct stream copy possible. Converting to MP3 would require transcoding from AAC to the MP3 codec (libmp3lame), which introduces an additional quality loss and takes longer. M4A with AAC also delivers better audio quality than MP3 at the same bitrate, and it is natively supported by all Apple devices and modern browsers.
Any metadata tags embedded in the CAVS audio stream — such as title, language, or track information — will be carried over during the remux. However, CAVS is a broadcast-oriented Chinese standard format that typically carries minimal iTunes-style metadata, so the M4A file may arrive with few or no tags. You can add standard iTunes metadata like artist, album, and artwork to the M4A file afterward using a tag editor such as Mp3tag or MusicBrainz Picard.
Yes. Replace the -b:a 128k value in the command with your desired bitrate. Common options are 64k for speech-quality audio, 96k for acceptable music, 192k for high-quality music, or 320k for near-transparent quality. Keep in mind that increasing the bitrate above the original CAVS audio bitrate will not recover detail that was not there — it will simply re-encode and potentially waste space. Lowering it will reduce file size at the cost of some fidelity.
On Linux or macOS you can run a shell loop: for f in *.cavs; do ffmpeg -i "$f" -vn -c:a aac -b:a 128k -vn "${f%.cavs}.m4a"; done. On Windows Command Prompt use: for %f in (*.cavs) do ffmpeg -i "%f" -vn -c:a aac -b:a 128k -vn "%~nf.m4a". This processes every CAVS file in the current directory and outputs a matching M4A file for each one. The browser-based tool handles one file at a time, so the FFmpeg command is particularly valuable for bulk workflows or files over 1GB.
This is redundant but harmless. The first -vn appears before the output filename as part of the output options and tells FFmpeg to exclude any video stream from the M4A file, which is the critical instruction. The second -vn in the resolved command is a duplicate that has no additional effect. When running the command yourself locally you can safely use just one -vn flag without any change in behavior.
Technical Notes
CAVS (Chinese Audio Video Standard) is a GB/T 20090 series national standard developed in China as an alternative to H.264, primarily used in Chinese digital broadcast infrastructure. Its audio component is AAC, the same codec used by M4A, which makes audio extraction from CAVS to M4A one of the cleanest possible stream-copy operations in FFmpeg — no transcoding pipeline, no codec negotiation overhead. The M4A container is technically an MPEG-4 Part 14 (.mp4) file restricted to audio streams, and it supports AAC, FLAC, Opus, and Vorbis codecs as well as chapter markers and iTunes-style metadata atoms. Because M4A does not support multiple audio tracks or subtitle streams, and CAVS itself does not support subtitles or chapters, there is no feature mismatch to worry about here. One known consideration: CAVS files encountered in the wild may have been mislabeled or wrapped in non-standard containers by Chinese broadcast hardware, which can occasionally confuse FFmpeg's format detection. If the tool reports an error, try renaming the file with a .avs extension and re-running. The 128k AAC default bitrate is appropriate for speech and general broadcast audio; for music archiving, 192k or 256k AAC is recommended.