Convert MTS to FLAC — Free Online Tool
Extract and preserve the audio track from your AVCHD camcorder footage (.mts) as a lossless FLAC file. This tool strips the H.264 video and transcodes the AC-3 or AAC audio stream into FLAC — giving you a perfect, bit-for-bit accurate audio archive without the overhead of the video container.
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 are AVCHD recordings from Sony or Panasonic camcorders, wrapping H.264 video alongside AC-3 or AAC audio inside an MPEG-2 Transport Stream container. Since FLAC is a pure audio format, the video stream is completely discarded during this conversion. The AC-3 or AAC audio track is decoded from the MTS file and then re-encoded using the FLAC codec at compression level 5. Unlike most conversions between audio formats, switching to FLAC is lossless — FLAC compression only reduces file size through mathematical encoding, not by discarding audio data. The resulting .flac file contains the full fidelity audio from your camcorder recording, including any stereo or multichannel audio, though FLAC supports only a single audio track, so if your MTS file contains multiple audio streams, only the default stream is extracted.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg media processing tool. In this browser-based tool, FFmpeg runs locally via WebAssembly (FFmpeg.wasm) — no data is sent to a server. |
-i input.mts
|
Specifies the input AVCHD file in MTS format — a MPEG-2 Transport Stream container carrying H.264 video and AC-3 or AAC audio as recorded by Sony or Panasonic camcorders. |
-c:a flac
|
Selects the FLAC codec to encode the output audio stream. The AC-3 or AAC audio from the MTS file is decoded to raw PCM and then re-encoded using lossless FLAC compression. No video codec is specified because FLAC is audio-only and the video stream is automatically dropped. |
-compression_level 5
|
Sets the FLAC compression effort to level 5 on a scale of 0–8. This controls encoding speed and file size but never affects audio quality, which is always bit-perfect. Level 5 is the standard default, offering a good balance between compression ratio and processing time for typical camcorder audio lengths. |
output.flac
|
Defines the output file as a FLAC audio file. The .flac extension tells FFmpeg to use the FLAC container, which stores the losslessly compressed audio along with any available metadata tags extracted from the source MTS file. |
Common Use Cases
- Archiving the audio from a wedding or event ceremony recording shot on a Sony or Panasonic camcorder, where the audio quality must be preserved perfectly for later editing or remastering
- Extracting a musical performance or live concert audio captured in AVCHD format to create a lossless master file before distributing in other formats
- Pulling the audio from a camcorder-recorded interview or documentary footage for use in an audio-only podcast or radio production without any generation loss
- Preserving the original on-camera audio from a film shoot as a lossless backup before the MTS files are transcoded or the memory card is wiped
- Creating a lossless FLAC reference file from camcorder footage to compare against separately recorded audio from a dedicated recorder during post-production sync
- Extracting ambient sound or field recordings captured incidentally on an AVCHD camcorder for use as lossless audio assets in a sound library
Frequently Asked Questions
No — FLAC is a lossless codec, meaning it perfectly reconstructs the original audio data with no loss. However, it is important to note that the process does involve decoding the source audio (AC-3 or AAC from the MTS file) and re-encoding it as FLAC. If the original MTS audio was AC-3 or AAC, those codecs are already lossy, so any quality reduction introduced during camcorder recording is already baked in. FLAC preserves exactly what is in the MTS audio track — it does not restore quality that was lost when the camcorder originally compressed the audio.
The video stream — which is H.264 encoded inside the AVCHD/MPEG-2 Transport Stream container — is completely discarded. FLAC is a pure audio format and has no capacity to store video data. Only the default audio track from the MTS file is decoded and preserved in the output FLAC file. If you need to keep the video, this conversion is not appropriate; you would need a video-preserving output format instead.
FLAC supports only a single audio track, so FFmpeg will extract the default audio stream from the MTS file, which is typically the first detected audio track. Some AVCHD recordings include a secondary audio track for dual-channel recording or language variants. If you need a specific non-default audio stream, you would need to modify the FFmpeg command locally by adding a stream selector such as '-map 0:a:1' to target a specific audio track by index.
The compression level in FLAC controls the trade-off between encoding speed and output file size — it has no effect on audio quality, which is always lossless. You can change the '-compression_level 5' value to any integer from 0 (fastest encoding, largest file) to 8 (slowest encoding, smallest file). For example, use '-compression_level 8' for the smallest possible FLAC file or '-compression_level 0' for the fastest conversion with a slightly larger file. Level 5 is the widely accepted default that balances speed and compression well.
Basic metadata that FFmpeg can read from the MTS container — such as creation timestamps or stream language tags — may be carried over, but rich camcorder-specific metadata like GPS coordinates, scene modes, or camera model information embedded in the AVCHD structure is typically not preserved in the FLAC output. FLAC supports standard audio metadata tags (title, artist, album, etc.) via Vorbis comments, but these fields are generally not populated from camcorder MTS files. You would need to add metadata tags manually after conversion using a tool like MusicBrainz Picard or Mp3tag.
The command shown processes a single file, but you can adapt it for batch processing in a terminal. On Linux or macOS, use a shell loop: 'for f in *.mts; do ffmpeg -i "$f" -c:a flac -compression_level 5 "${f%.mts}.flac"; done'. On Windows Command Prompt, use: 'for %f in (*.mts) do ffmpeg -i "%f" -c:a flac -compression_level 5 "%~nf.flac"'. This is particularly useful when offloading an entire AVCHD memory card of recordings at once.
Technical Notes
AVCHD MTS files typically carry AC-3 (Dolby Digital) audio at 48 kHz, often recorded at 256 kbps stereo or 5.1 surround from Sony and Panasonic camcorders, though some models use AAC instead. Both AC-3 and AAC are lossy codecs, so the FLAC output file faithfully represents the audio as it was stored on the camcorder — losslessly encoding those already-compressed PCM samples after decoding. Because FLAC uses lossless compression, the output file size will typically be significantly smaller than uncompressed WAV would be, but notably larger than the original AAC or AC-3 stream in the MTS — this is expected, as FLAC is measured against PCM, not lossy codecs. The 48 kHz sample rate common in AVCHD recordings is fully supported by FLAC. Multichannel audio (e.g., 5.1 surround from professional AVCHD cameras) is preserved in channel count, though if the source is true 5.1 AC-3, all six channels will be present in the output FLAC. One known limitation is that FLAC does not support chapters or cue sheet embedding in this workflow, and subtitle or timecode data from the transport stream is not transferable to FLAC.