Extract Audio from MTS to FLAC — Free Online Tool
Extract lossless audio from AVCHD camcorder footage (.mts files) and save it as FLAC. This tool strips the H.264 video stream and re-encodes the AC-3 or AAC audio track from your MTS file into FLAC's lossless compression format, preserving every bit of audio fidelity from your original recording.
to
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 from Sony and Panasonic camcorders store audio as either AC-3 (Dolby Digital) or AAC inside an MPEG-2 Transport Stream container. Because FLAC is a lossless format and AC-3/AAC are lossy codecs, this conversion cannot be truly 'lossless' in the absolute sense — the audio was already lossy-compressed in the camera. What FLAC guarantees is that the decoded audio data from your MTS file is captured and stored without any additional quality loss: no second-generation compression artifacts are introduced. The tool discards the video stream entirely using the -vn flag, decodes the audio from the transport stream, and re-encodes it into FLAC at compression level 5 — which affects only file size and encoding speed, never audio quality.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg tool. In the browser-based version of this tool, FFmpeg runs locally via WebAssembly (FFmpeg.wasm) — your MTS file never leaves your device. |
-i input.mts
|
Specifies the input AVCHD file in MTS format. FFmpeg reads and demuxes the MPEG-2 Transport Stream, separating the H.264 video stream and the AC-3 or AAC audio stream for processing. |
-vn
|
Disables video output entirely. This tells FFmpeg to ignore the H.264 video stream from the MTS file, so only the audio track is processed and written to the FLAC output — essential for audio-only extraction. |
-c:a flac
|
Sets the audio codec to FLAC (Free Lossless Audio Codec). FFmpeg decodes the AC-3 or AAC audio from the MTS source and re-encodes it into FLAC's lossless format, introducing no further quality loss beyond what was already present in the camcorder's original recording. |
-compression_level 5
|
Sets the FLAC compression level to 5 on a scale of 0–8. This controls only the trade-off between encoding speed and output file size — all levels of FLAC compression produce audio that is bit-for-bit identical on playback. Level 5 is the default and offers a good balance for typical camcorder audio files. |
output.flac
|
Specifies the output filename with the .flac extension. FFmpeg uses this extension to confirm the FLAC container format and writes the losslessly compressed audio extracted from your MTS camcorder file. |
Common Use Cases
- Archiving the clean audio from wedding or event footage shot on a Sony or Panasonic AVCHD camcorder before handing the video off to an editor
- Extracting high-quality interview audio from MTS camcorder clips to use as source material in a podcast or documentary without introducing extra compression artifacts
- Pulling ambient sound or field recordings captured on an AVCHD camcorder to use as stems in a music production or sound design project
- Creating a lossless audio archive of a live performance recorded in MTS format so the audio can be re-encoded to any format later without quality degradation
- Extracting the audio track from MTS footage to sync it with a separate audio recorder's track in a double-system sound workflow
- Saving the audio from family camcorder MTS recordings separately as FLAC for long-term digital preservation alongside the video files
Frequently Asked Questions
Not in the absolute sense — AC-3 (Dolby Digital), which is common in AVCHD camcorders, is itself a lossy codec. When FFmpeg decodes the AC-3 stream and re-encodes it to FLAC, no additional quality is lost compared to the AC-3 source. However, the audio was already compressed with some loss when the camcorder originally recorded it. FLAC simply ensures you do not lose any further quality beyond what the camera already introduced.
Some AVCHD camcorders record AC-3 5.1 surround audio, which FFmpeg will preserve in the FLAC output — FLAC supports multi-channel audio. However, if your camcorder recorded stereo (which is most common in consumer models), the output will naturally be stereo. If you are getting an unexpected channel count, check your original MTS file with a tool like MediaInfo to confirm the source channel layout before converting.
The FLAC file will typically be larger than the compressed audio inside the MTS container because FLAC stores audio in lossless form while AC-3 or AAC achieves smaller sizes through lossy compression. For typical camcorder audio, a FLAC file might be 3–6 times larger than the equivalent AC-3 audio data. The video stream, which makes up the vast majority of an MTS file's size, is discarded entirely, so the FLAC output will still be much smaller than the original MTS file overall.
You can change the compression level by adjusting the -compression_level value, which accepts integers from 0 to 8. Level 0 encodes fastest with the largest file size, while level 8 encodes slowest with the smallest file size. Crucially, all levels produce bit-for-bit identical audio — compression level only affects encoding speed and file size, never audio quality. The default of 5 is a well-balanced midpoint for most users.
Yes. Many AVCHD camcorders record multiple audio streams (for example, a main microphone track and a secondary input). By default, FFmpeg selects the first audio stream. To target a specific track, add -map 0:a:1 before the output filename to select the second audio stream (index 1), or -map 0:a:0 for the first. The full command would look like: ffmpeg -i input.mts -vn -map 0:a:1 -c:a flac -compression_level 5 output.flac.
FFmpeg will attempt to copy any metadata tags embedded in the MTS container to the FLAC output, but AVCHD transport streams carry limited standardized metadata compared to formats like MP4. Recording timestamps may transfer, but camera-specific metadata (model, GPS coordinates, scene settings) stored in proprietary AVCHD structures is typically not accessible or preserved. FLAC supports rich metadata via Vorbis comments, so you can add tags manually after conversion using a tool like fre:ac or Mp3tag.
Technical Notes
AVCHD MTS files use the MPEG-2 Transport Stream container, which was designed for broadcast and streaming reliability rather than clean metadata handling — this is why extracting audio can occasionally produce timing quirks. FFmpeg handles MTS demuxing well but may apply a small amount of timestamp correction when building the FLAC output. The audio in AVCHD recordings is almost always AC-3 at 48 kHz (common in Sony camcorders) or AAC at 48 kHz (more common in Panasonic models); FLAC will preserve the 48 kHz sample rate exactly, which is important to note if you plan to use the audio in a project defaulting to 44.1 kHz. FLAC does not support chapters or subtitle streams, but since this conversion extracts only audio, neither is relevant. The -vn flag is essential here — without it, FFmpeg would attempt to find a video codec compatible with FLAC's container, which would fail. One known edge case: some older MTS files from early AVCHD camcorders use a non-standard AC-3 wrapping that causes FFmpeg to emit warnings during demux; the audio output is usually correct despite these warnings.