Extract Audio from MTS to M4A — Free Online Tool
Extract audio from AVCHD camcorder footage (.mts) and save it as an M4A file with AAC encoding — perfect for pulling interview audio, event recordings, or ambient sound from Sony or Panasonic camcorder clips without any server upload.
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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
MTS files use an MPEG-2 Transport Stream container, typically carrying H.264 video alongside AC-3 or AAC audio tracks recorded by the camcorder. This tool strips the video stream entirely and re-encodes the audio as AAC at 128k bitrate inside an MPEG-4 (.m4a) container. If the source MTS file already contains an AAC audio track, the re-encoding step is technically redundant but ensures clean container compatibility. If the camcorder recorded AC-3 (Dolby Digital) audio — common on many AVCHD devices — that track is fully decoded and transcoded to AAC, making the output universally playable on Apple devices, browsers, and podcast platforms without needing AC-3 decoder support.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg program, the open-source multimedia processing engine running under the hood of this browser tool via WebAssembly (FFmpeg.wasm). All conversion logic is executed locally in your browser using this engine. |
-i input.mts
|
Specifies the input file — your AVCHD camcorder clip in MTS format. FFmpeg reads the MPEG-2 Transport Stream container and demuxes its H.264 video and AC-3 or AAC audio elementary streams for processing. |
-vn
|
Disables video output, telling FFmpeg to ignore the H.264 video stream from the MTS file entirely. This is essential for audio extraction — without it, FFmpeg would attempt to include or re-encode the video track, which is unwanted in an audio-only M4A file. |
-c:a aac
|
Sets the audio codec to AAC (Advanced Audio Coding) using FFmpeg's built-in AAC encoder. AAC is the native and default codec for M4A files and is required for compatibility with Apple iTunes, iOS devices, and most podcast platforms. If the MTS source contains AC-3 audio, this triggers a full decode-and-reencode transcode; if it's already AAC, it still re-encodes into the new container. |
-b:a 128k
|
Sets the AAC audio output bitrate to 128 kilobits per second, which is the standard default balancing file size and audio quality. For camcorder speech recordings this is generally sufficient; for music or high-fidelity event audio extracted from a high-bitrate AVCHD source, consider increasing this to 192k or 256k. |
-vn
|
A second instance of the video-disable flag applied at the output stage. While redundant given the earlier '-vn', it explicitly enforces that no video stream is mapped into the output M4A file, ensuring a clean audio-only result regardless of stream auto-selection behavior. |
output.m4a
|
Defines the output filename with the .m4a extension, which tells FFmpeg to wrap the encoded AAC audio in an MPEG-4 audio container. The .m4a extension (as opposed to .mp4) signals to Apple software and media players that this is an audio-only file, enabling correct library import and metadata handling in iTunes and Music apps. |
Common Use Cases
- Pull the audio from a Sony or Panasonic camcorder interview recording to edit in a podcast or voiceover project
- Extract ambient sound or event audio from AVCHD wedding or concert footage to use as a standalone audio file
- Convert camcorder MTS clips to M4A for playback in iTunes, Apple Music, or on iOS devices that don't support raw AVCHD
- Separate the audio commentary from a camcorder-recorded presentation or lecture for distribution as a podcast episode
- Archive the audio track from old MTS camcorder recordings in a compact, widely supported format before the original files are deleted or stored offline
- Prepare audio extracted from AVCHD footage for upload to platforms like Spotify or Apple Podcasts, which accept M4A/AAC natively
Frequently Asked Questions
It depends on the audio codec in your original MTS file. If the camcorder recorded AC-3 (Dolby Digital) audio, converting to AAC involves decoding AC-3 and re-encoding as AAC at 128k — a lossy-to-lossy transcode that introduces a small amount of generational quality loss. If the source already has AAC audio, the re-encoding is still performed but the quality difference at 128k is negligible for speech and most music. For critical archival work, you can increase the bitrate to 256k or 320k using the FFmpeg command shown on this page.
Some AVCHD camcorders record a secondary audio track, such as a backup channel from a secondary microphone or a stereo/5.1 downmix variant. By default, the FFmpeg command on this page extracts only the first audio track. M4A does not support multiple audio tracks in a single file, so if you need a specific track, you can modify the command by adding '-map 0:a:1' to select the second audio stream instead of the default first stream.
Yes, marginally. Sony camcorders typically record AVCHD with AAC stereo audio, while Panasonic models more commonly use AC-3 (Dolby Digital) at 256k or higher. The AC-3 source generally has a bit more headroom, so transcoding it to AAC at 128k may result in a slightly more noticeable quality reduction compared to AAC-to-AAC conversion. Both cases are handled automatically by this tool, but the original camcorder audio bitrate sets the ceiling for output quality regardless of the setting you choose.
In the command 'ffmpeg -i input.mts -vn -c:a aac -b:a 128k -vn output.m4a', replace '128k' in the '-b:a 128k' flag with your desired bitrate — for example, '-b:a 256k' for higher fidelity or '-b:a 96k' for a smaller file. For extracting speech from a camcorder interview, 128k is typically sufficient. For music or high-quality event audio where the original recording was captured at a high bitrate, 192k or 256k is recommended to preserve more of the source detail.
Yes. On Linux or macOS, you can run: 'for f in *.mts; do ffmpeg -i "$f" -vn -c:a aac -b:a 128k -vn "${f%.mts}.m4a"; done' in your terminal. On Windows Command Prompt, use: 'for %f in (*.mts) do ffmpeg -i "%f" -vn -c:a aac -b:a 128k -vn "%~nf.m4a"'. This is particularly useful for processing a full memory card's worth of AVCHD clips from a camcorder shoot. The browser tool processes one file at a time, so the FFmpeg command is the recommended approach for bulk conversions.
AVCHD MTS files embed limited metadata in the transport stream, often including recording timestamps. FFmpeg will attempt to carry over any recognized metadata tags to the M4A container, but AVCHD-specific camcorder metadata (such as GPS coordinates or scene mode stored in proprietary AVCHD structures) is generally not preserved since M4A uses iTunes-style metadata atoms that have no equivalent fields for that data. Standard tags like creation time may transfer, but you should not rely on the M4A output to retain full AVCHD metadata fidelity.
Technical Notes
MTS is a strict subset of the MPEG-2 Transport Stream format specified by the AVCHD standard, and its audio payload is almost always either AC-3 (Dolby Digital, typically at 256k stereo or 5.1 surround) or AAC-LC in a fixed-length packetized elementary stream. FFmpeg handles both transparently. The output M4A container is an MPEG-4 Part 14 file with an audio-only constraint — the same underlying container as MP4 but with the .m4a extension signaling audio-only content, which allows iTunes and Apple Music to import it correctly as a music or podcast file. The '-vn' flag appears twice in the generated command (once before and once after the codec flags), which is harmless — the second instance reinforces the video exclusion at the output mapping stage. One known limitation: if your MTS file contains a 5.1 surround AC-3 track, the default AAC encoder in FFmpeg will downmix it to stereo unless you explicitly pass '-ac 6' and an AAC encoder that supports multi-channel output. For camcorder footage this is rarely an issue since most consumer AVCHD recordings are stereo, but broadcast or professional AVCHD sources may warrant checking the channel layout with 'ffprobe' before converting.