Extract Audio from M2TS to M4B — Free Online Tool
Extract audio from M2TS Blu-ray and AVCHD files and save it as M4B, the MPEG-4 audiobook format with chapter and bookmarking support. This tool strips the video stream entirely and encodes the audio as AAC inside an M4B container — ideal for turning recorded lectures, concerts, or long-form video content into a portable, bookmark-friendly audio file.
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
M2TS files from Blu-ray discs and AVCHD camcorders typically carry audio encoded as AC-3 (Dolby Digital), DTS, or PCM alongside high-definition H.264 or H.265 video. This tool discards the video stream entirely using the -vn flag and re-encodes whichever audio track is present into AAC — the only codec natively supported for playback in M4B files on Apple devices and most podcast players. The resulting M4B container is structured with the -movflags +faststart optimization, which moves the file index to the beginning of the file, enabling faster playback start. Because M4B is inherently a single-audio-track format, only the default audio track from the M2TS source is extracted; if your M2TS has multiple language tracks, the primary track is selected automatically.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg program. When run in the browser, this is executed via FFmpeg.wasm (WebAssembly), a fully client-side port of FFmpeg — no file data is sent to any server. |
-i input.m2ts
|
Specifies the input M2TS file, which is a Blu-ray or AVCHD container potentially containing H.264/H.265 video, high-definition audio (PCM, AC-3, DTS, or TrueHD), and subtitle streams. |
-vn
|
Disables video output entirely, telling FFmpeg to ignore all video streams in the M2TS source. This is essential since M4B is a pure audio container and cannot hold video data. |
-c:a aac
|
Re-encodes the audio stream to AAC-LC using FFmpeg's built-in AAC encoder. This transcode step is mandatory because M2TS audio codecs (AC-3, DTS, PCM, TrueHD) are incompatible with the M4B/MPEG-4 container. |
-b:a 128k
|
Sets the AAC audio bitrate to 128 kilobits per second, which is the default and provides reasonable quality for speech and moderate-quality music. Increase to 256k or 320k if your M2TS source contained high-bitrate or lossless audio and you want to minimize quality loss. |
-movflags +faststart
|
Moves the M4B file's metadata index (the moov atom) to the start of the file. This is a required flag for M4B files to enable immediate playback and proper audiobook behavior in Apple Books, iPhone, and podcast applications without needing to read the entire file first. |
output.m4b
|
Specifies the output filename with the .m4b extension, which signals to Apple devices and audiobook players that this MPEG-4 audio file should be treated as an audiobook, enabling bookmarking and resume functionality rather than standard music playback. |
Common Use Cases
- Convert a Blu-ray rip of a recorded lecture series or university course into M4B so you can listen with bookmarking in Apple Books or a podcast app, resuming exactly where you left off
- Turn an AVCHD camcorder recording of a live concert, theater performance, or spoken-word event into a portable M4B audiobook file for distraction-free listening
- Extract audio commentary tracks from Blu-ray M2TS files and package them as M4B files for easy playback alongside the film without needing the video
- Convert long-form documentary or interview recordings captured in M2TS format into M4B for distribution as podcast episodes or audio courses
- Archive the audio from AVCHD home video recordings of family events into M4B format, which supports chapter markers for organizing long recordings by scene or time
- Prepare audio from a Blu-ray-sourced M2TS recording of a conference keynote or panel discussion as an M4B file for listeners who want audiobook-style chapter navigation
Frequently Asked Questions
Almost certainly yes, because M2TS files from Blu-ray sources commonly carry lossless (PCM, Dolby TrueHD) or high-bitrate lossy (AC-3, DTS) audio, and converting any of these to AAC at 128k is a lossy transcode. The degree of perceptible quality loss depends on your source — lossless PCM to AAC 128k will be more noticeable than AC-3 192k to AAC 128k. If quality matters, increase the -b:a value to 256k or 320k in the FFmpeg command before running the conversion.
M4B natively supports chapters, which is one of the main reasons it is used for audiobooks and long-form audio. However, M2TS files do not store chapters in a format that FFmpeg automatically maps to M4B chapter markers during this extraction. If you want chapter markers in your output M4B, you would need to add them separately using a tool like mp4chaps or by embedding a chapter metadata file with FFmpeg's -metadata_from_file flag after the initial conversion.
FFmpeg selects the default audio stream, which is typically the first audio track in the M2TS container. M4B does not support multiple audio tracks, so only one can be included. If you need a specific non-default track, you can modify the command by adding -map 0:a:1 (for the second audio stream) before the output filename, replacing the index number with whichever track you need.
M4B and M4A use the identical MPEG-4 container and AAC audio encoding — the only difference is the file extension and a flag in the container header that signals to Apple software that the file is an audiobook rather than music. The .m4b extension enables bookmarking behavior in Apple Books, iPhone, and iTunes, so the player remembers your position. Using .m4a would produce a functionally identical audio file but without the bookmarking behavior on Apple devices.
Replace the 128k value in the -b:a 128k portion of the command with your desired bitrate. For example, use -b:a 256k for higher quality output suitable for music or detailed speech, or -b:a 64k for smaller file sizes when audio quality is less critical (such as voice-only recordings). The full modified command would look like: ffmpeg -i input.m2ts -vn -c:a aac -b:a 256k -movflags +faststart output.m4b.
The command shown processes a single file, but you can batch process on your desktop using a shell loop. On Linux or macOS, run: for f in *.m2ts; do ffmpeg -i "$f" -vn -c:a aac -b:a 128k -movflags +faststart "${f%.m2ts}.m4b"; done. On Windows PowerShell: Get-ChildItem *.m2ts | ForEach-Object { ffmpeg -i $_.FullName -vn -c:a aac -b:a 128k -movflags +faststart ($_.BaseName + '.m4b') }. The browser-based tool processes one file at a time.
Technical Notes
M2TS is a strict superset of the MPEG-2 Transport Stream format, designed for Blu-ray and AVCHD, and can carry a wide variety of audio codecs including PCM, Dolby TrueHD, AC-3, E-AC-3, DTS, and DTS-HD MA — none of which are compatible with the M4B container. This means audio re-encoding to AAC is always required; there is no lossless remux path for this format pair. The AAC encoder used here is FFmpeg's native aac encoder, which produces broadly compatible AAC-LC output. If you need higher-fidelity AAC encoding, the libfdk_aac encoder (not included in standard FFmpeg builds) would produce marginally better results at the same bitrate, but the native encoder is perfectly adequate for speech and most music at 128k and above. The -movflags +faststart flag reorganizes the MP4/M4B atom structure so the moov atom (file index) is placed before the mdat (media data), which is important for streaming and fast playback initiation. ID3-style metadata tags (title, artist, album) from the M2TS source are not automatically carried over and would need to be embedded manually using -metadata flags. M4B does not support subtitles, so any subtitle streams in the M2TS source are silently dropped.