Convert MP4 to M4A — Free Online Tool
Extract audio from an MP4 video and save it as an M4A file using AAC encoding — the same codec already used in most MP4s, making this a fast, near-lossless stream extraction rather than a full re-encode. M4A is the preferred audio container for iTunes, Apple Music, and podcast workflows, with excellent support across iOS, macOS, and modern browsers.
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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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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
Most MP4 files store their audio as an AAC stream, and M4A is simply an MPEG-4 container that holds audio-only AAC data. Because both formats share the same underlying codec, this conversion works by stripping the video stream entirely and remuxing the AAC audio into the M4A container — no audio decoding or re-encoding is required at the default settings. The result is that audio quality is preserved exactly as it was in the source MP4, and processing is extremely fast since the raw audio data is copied rather than transformed. The -vn flag discards all video, subtitle, and other non-audio streams, while the output container extension (.m4a) signals FFmpeg to wrap the audio in an iTunes-compatible MPEG-4 audio file. Chapter markers present in the source MP4 are also carried over to the M4A output.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg binary — the open-source multimedia processing engine that powers this conversion. In the browser, this runs as a WebAssembly build (FFmpeg.wasm) with no server involvement. |
-i input.mp4
|
Specifies the input file — your source MP4 containing both video and audio streams. FFmpeg will read all streams from this container and allow you to selectively process or discard them. |
-c:a aac
|
Sets the audio codec to AAC (Advanced Audio Coding). Since most MP4 files already contain an AAC audio stream, FFmpeg can copy or lightly re-encode it directly into the M4A container without a costly decode-encode cycle, preserving quality. |
-b:a 128k
|
Sets the audio bitrate to 128 kilobits per second, which is the default for this tool and delivers acceptable quality for speech and general music. Increase to 192k or 256k for higher-fidelity music output in M4A. |
-vn
|
Disables video output entirely — this is the critical flag that transforms an MP4 video file into an audio-only M4A file by instructing FFmpeg to discard the video stream and any other non-audio streams before writing the output. |
output.m4a
|
Specifies the output filename with the .m4a extension. FFmpeg uses this extension to determine the output container format — MPEG-4 audio — which is the iTunes-compatible wrapper that holds the extracted AAC audio stream. |
Common Use Cases
- Strip the audio track from a recorded video lecture or webinar to create a portable audio file you can listen to on your iPhone or Apple Watch via the Podcasts or Music app
- Extract a music performance or concert video's audio into M4A for import into iTunes or Apple Music as a high-quality personal library track with full metadata support
- Pull the audio from a screencasted software tutorial to produce a podcast episode or audio companion, keeping the AAC quality intact without an extra encoding step
- Archive the audio commentary or narration from an MP4 training video as a standalone M4A file for distribution to learners who only need audio
- Extract multi-chapter audiobook audio from an MP4 recording, preserving the chapter structure in the M4A output for navigation in compatible players like Overcast or Apple Podcasts
- Prepare audio from a branded video file for upload to Apple Podcasts or iTunes Connect, which requires AAC audio in an MPEG-4 container — exactly what M4A provides
Frequently Asked Questions
In most cases, no — not in any meaningful way. The vast majority of MP4 files already contain AAC audio, and this tool remuxes that AAC stream directly into the M4A container without decoding and re-encoding it. When the source audio is copied rather than transcoded, there is no generation loss. Quality degradation would only occur if you explicitly changed the audio bitrate to something lower than the source, or if the source MP4 used a non-AAC codec that required transcoding to AAC.
The video stream in an MP4 typically accounts for 80–95% of the total file size. When you extract only the audio into M4A and discard the video with -vn, you are left with just the audio data, which explains the dramatic size reduction. A 500 MB MP4 video might produce a 30–50 MB M4A audio file, depending on the original audio bitrate and duration. This is expected and correct — no audio data is being lost or compressed further.
M4A is natively supported on all Apple devices and software, modern browsers, and VLC. However, compatibility varies elsewhere: Spotify does not accept M4A uploads for local files (it prefers MP3 or OGG), older versions of Windows Media Player have limited M4A support without codec packs, and some Android media players may not support it natively. If broad cross-platform compatibility is your goal, converting to MP3 instead may be more practical, though you would sacrifice a small amount of audio quality due to AAC-to-MP3 transcoding.
Yes. M4A supports chapter markers, and FFmpeg will carry over any chapters embedded in the source MP4 to the output M4A file. This makes it particularly useful for audiobooks and long-form podcast recordings where chapter navigation is important. The chapters will be readable in chapter-aware players like Apple Podcasts, Overcast, and most MPEG-4-compliant audio players.
Replace the value after -b:a with your desired bitrate. For example, use -b:a 192k for higher quality or -b:a 96k for a smaller file. The default in this tool is 128k, which is a reasonable balance for speech and music. For music archival or audiophile use, 256k or 320k is recommended. Note that if the source MP4 audio is already encoded at a lower bitrate than your target, increasing the bitrate will not recover lost quality — it will only inflate the file size.
Yes. On Linux or macOS, you can run a simple shell loop: for f in *.mp4; do ffmpeg -i "$f" -c:a aac -b:a 128k -vn "${f%.mp4}.m4a"; done. On Windows Command Prompt, use: for %f in (*.mp4) do ffmpeg -i "%f" -c:a aac -b:a 128k -vn "%~nf.m4a". This applies the same extraction logic to every MP4 in the current directory, which is especially useful when processing large files over 1GB that exceed browser-based tool limits.
Technical Notes
The MP4 and M4A formats are both built on the ISO Base Media File Format (ISOBMFF), which means they share the same structural DNA. M4A is essentially an MP4 file with an audio-only constraint and the .m4a file extension, which Apple introduced to distinguish audio-only MPEG-4 files from video-bearing MP4s. Because of this shared foundation, remuxing AAC audio from MP4 to M4A is one of the most efficient conversions FFmpeg can perform — it is largely a container restructuring operation. One notable limitation: M4A does not support multiple audio tracks or subtitle tracks, so if your source MP4 contains several language audio streams or embedded subtitles, only the default audio track will be extracted and all subtitles will be discarded. Metadata such as title, artist, and album tags present in the MP4 are generally preserved in the M4A output, and iTunes-specific metadata atoms (iTunSMPB for gapless playback, for example) may be written by some encoders. If you need lossless audio, the M4A container also supports FLAC encoding, which can be achieved by changing the codec flag to -c:a flac in the command, though this requires re-encoding from the lossy AAC source and cannot recover any quality lost during the original MP4 encoding.