Convert MTS to ALAC — Free Online Tool
Extract and convert the audio from AVCHD camcorder footage (.mts) into Apple Lossless (ALAC) format — a perfect way to archive high-quality audio from your recordings without any lossy compression. The AC-3 or AAC audio track from your MTS file is transcoded into lossless ALAC, stored in an MPEG-4 container (.m4a), and fully compatible with iTunes, Apple Music, and any Core Audio–based application.
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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
MTS files from Sony and Panasonic camcorders use the AVCHD standard, packaging H.264 video with AC-3 or AAC audio inside an MPEG-2 Transport Stream container. This conversion discards the video stream entirely and transcodes only the audio track into ALAC — Apple's lossless codec stored in an .m4a (MPEG-4) container. Because ALAC is lossless, the output represents a mathematically perfect reconstruction of the decoded audio signal from your camcorder — no further quality is lost beyond whatever lossy compression (AC-3 or AAC) was applied during original recording. The result is a clean, universally Apple-compatible audio file ideal for archiving, music production imports, or iTunes library integration.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg binary — the open-source multimedia processing engine that powers this conversion both in the browser (via FFmpeg.wasm) and on the command line. |
-i input.mts
|
Specifies the input AVCHD file in MTS format, as produced by Sony or Panasonic camcorders. FFmpeg reads the MPEG-2 Transport Stream container and demuxes the H.264 video and AC-3/AAC audio streams contained within. |
-c:a alac
|
Sets the audio codec to ALAC (Apple Lossless Audio Codec). FFmpeg decodes the source AC-3 or AAC audio from the MTS file to raw PCM and then re-encodes it losslessly using ALAC, ensuring no additional quality is lost beyond the original camcorder recording. |
-c:a alac
|
This flag appears twice in the resolved command — the second instance is redundant but harmless, as FFmpeg applies the last valid value for each stream selector. Both instances confirm the ALAC codec for the audio output stream. |
output.m4a
|
Defines the output filename with the .m4a extension, which signals FFmpeg to wrap the ALAC audio stream in an MPEG-4 container — the standard and required container for ALAC files, ensuring compatibility with iTunes, Apple Music, iOS, and macOS. |
Common Use Cases
- Archive the audio from a live event or concert recorded on a Sony or Panasonic AVCHD camcorder, preserving every detail of the decoded audio in a lossless format for long-term storage.
- Import location audio or ambient sound recorded on a camcorder into Logic Pro or GarageBand as a lossless ALAC file for use in music production or sound design.
- Strip the spoken audio from a lecture, interview, or documentary shot on an AVCHD camcorder to create a high-quality audio-only archive in Apple Lossless for transcription or podcast editing.
- Transfer camcorder audio into iTunes or Apple Music by converting MTS footage to ALAC .m4a, which is natively recognised and playable without any additional plugins.
- Preserve the best possible audio fidelity when repurposing video footage — extract the ALAC audio as an archival master before later exporting lossy versions (MP3, AAC) for distribution.
- Prepare clean audio stems from multi-camera AVCHD shoots by extracting each camera's audio track into individual lossless ALAC files for mixing in a DAW.
Frequently Asked Questions
No — ALAC is lossless, but it cannot recover quality that was already discarded during the original AVCHD recording. Your camcorder encoded the audio as AC-3 (Dolby Digital) or AAC, both of which are lossy formats. What ALAC guarantees is that no additional quality is lost during this conversion: the decoded audio signal from your MTS file is preserved bit-for-bit in the ALAC output. Think of it as the best possible archive of what the camcorder actually captured.
ALAC (Apple Lossless Audio Codec) is specifically designed to be stored inside an MPEG-4 container, which uses the .m4a file extension for audio-only files. This is the format Apple defined and it is what ensures full compatibility with iTunes, Apple Music, iOS, and macOS Core Audio. If you need a different lossless container such as FLAC in an OGG wrapper, you would need a different conversion — ALAC is intrinsically tied to the .m4a/.mp4 container.
The default FFmpeg command targets the first audio stream from your MTS file, which covers the vast majority of camcorder footage. However, AVCHD files can occasionally contain multiple audio streams (for example, a main stereo mix and a secondary track). ALAC in an .m4a container does not support multiple independent audio tracks in the way MKV or MTS can. If your footage has multiple streams, only the primary one will be included in the output unless you modify the command to explicitly select a specific stream with the -map flag.
The output .m4a will contain only the audio — no video — so it will be dramatically smaller than the source MTS file. A typical AVCHD video at 1080p might be 5–20 GB per hour, while the extracted ALAC audio for the same duration is usually 200–600 MB per hour depending on channel count and sample rate. ALAC itself achieves roughly 40–60% compression compared to uncompressed PCM, so it is more compact than a WAV equivalent while remaining lossless.
Yes. On macOS or Linux, you can loop over all MTS files in a folder using a shell command such as: for f in *.mts; do ffmpeg -i "$f" -c:a alac "${f%.mts}.m4a"; done. On Windows Command Prompt, use: for %f in (*.mts) do ffmpeg -i "%f" -c:a alac "%~nf.m4a". This applies the same conversion logic to every file in sequence, producing one .m4a per .mts input.
AVCHD MTS files embed limited metadata in the MPEG-2 Transport Stream container, and FFmpeg will attempt to map compatible tags (such as creation time) into the MPEG-4 container's metadata fields. However, camera-specific metadata embedded in the AVCHD stream (such as GPS data or proprietary Sony/Panasonic tags) may not transfer completely. ALAC in .m4a does support standard iTunes-style metadata tags (title, artist, album, year), which you can add or edit after conversion using a tag editor like MusicBrainz Picard or Apple's own tools.
Technical Notes
AVCHD MTS files present a few specific parsing considerations for FFmpeg. The MPEG-2 Transport Stream container uses a byte-stream multiplexing scheme that can occasionally cause FFmpeg to misread stream timestamps at the start of a file — if you notice sync issues or a truncated output, prepending -fflags +genpts to the command can help FFmpeg regenerate presentation timestamps. The audio in MTS files is most commonly AC-3 at 48 kHz stereo or 5.1 surround, or AAC at 48 kHz; in both cases FFmpeg fully decodes these to PCM before re-encoding to ALAC, so no intermediate quality step is skipped. ALAC supports sample rates up to 384 kHz and bit depths of 16 or 24 bits — camcorder audio is typically 16-bit/48 kHz, which ALAC handles natively. There are no quality tuning parameters for ALAC since it is lossless by definition; the only variable is the source audio's fidelity. Note also that ALAC does not support subtitle tracks, so any subtitle or caption data in the MTS file will not be carried over — though audio-only conversions rarely require this.