Convert M2TS to M4B — Free Online Tool
Convert M2TS Blu-ray or AVCHD video files into M4B audiobooks by extracting and re-encoding the audio track to AAC inside an MPEG-4 container with full chapter and bookmarking support. Ideal for turning recorded lectures, concerts, or long-form video content into a portable audiobook format playable in Apple Books, Overcast, and compatible podcast apps.
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 is a BDAV MPEG-2 Transport Stream container typically carrying H.264 or H.265 video alongside multi-channel audio encoded as AC-3 (Dolby Digital), DTS, or LPCM. M4B is a pure audio format — it has no video track — so this conversion is not a remux but a full transcode of the audio stream. FFmpeg discards the video stream entirely and re-encodes the audio (whatever codec it uses in the M2TS) into AAC at 128k bitrate, wrapping it inside an MPEG-4 container with the .m4b extension. The -movflags +faststart flag repositions the MPEG-4 metadata header to the beginning of the file, enabling progressive playback and streaming before the full file has loaded. Chapter markers from the source M2TS are not automatically carried over because M4B chapters use a different metadata structure (QuickTime chapter tracks), but the output container is fully capable of holding them if added separately.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg multimedia processing tool. This command runs entirely in your browser via FFmpeg.wasm (WebAssembly) without uploading your file to any server, but the identical command can be run locally on your desktop for files larger than 1GB. |
-i input.m2ts
|
Specifies the input file as an M2TS container — a BDAV MPEG-2 Transport Stream carrying the Blu-ray or AVCHD video, audio, and subtitle streams that FFmpeg will demux and process. |
-c:a aac
|
Instructs FFmpeg to re-encode the audio stream to AAC using its built-in native AAC encoder. This transcode is mandatory because M4B does not support the AC-3, DTS, or LPCM codecs commonly found in M2TS files from Blu-ray sources. |
-b:a 128k
|
Sets the AAC audio bitrate to 128 kilobits per second, which is a reasonable default for speech and general listening. Increase to 192k or 256k for music or high-fidelity Blu-ray audio sources where the additional bitrate will help compensate for the lossy transcode from LPCM or DTS-HD. |
-movflags +faststart
|
Moves the MPEG-4 moov atom (the file's metadata and index block) to the beginning of the output file after encoding completes. This is required for M4B files to stream progressively and for Apple Books to correctly recognize chapters and enable bookmarking before the entire file is read. |
output.m4b
|
Specifies the output filename with the .m4b extension, which signals to Apple Books, Overcast, and other audiobook players that the file supports bookmarking, chapter navigation, and variable playback speed — features not activated by the otherwise identical .m4a extension. |
Common Use Cases
- Extract the audio from a recorded Blu-ray lecture series or educational disc to create a self-contained M4B audiobook you can listen to offline in Apple Books with bookmarking support
- Convert an AVCHD camcorder recording of a conference keynote or seminar into an M4B file so listeners can resume playback exactly where they left off on their iPhone or iPad
- Turn a long-form Blu-ray concert or opera recording into an M4B audio file for background listening without needing a video screen or high-bandwidth stream
- Strip the audio from an M2TS home video archive to produce a compact M4B memoir or personal audio diary that is compatible with audiobook apps and preserves a small file footprint
- Re-package an AVCHD interview recording into M4B format for podcast-style distribution via RSS feeds that support the M4B container
- Prepare audio extracted from a Blu-ray documentary for use in an Apple Podcasts-compatible M4B feed, leveraging the format's native chapter and bookmarking metadata capabilities
Frequently Asked Questions
No. M4B is an audio-only format derived from MPEG-4, so FFmpeg automatically drops all video streams during this conversion. Only the first audio track from the M2TS is extracted and re-encoded to AAC. If your M2TS contains multiple audio tracks — for example, a main mix and a director's commentary — only the default (first) track is included in the output unless you modify the FFmpeg command to select a specific stream with -map 0:a:1 or similar.
Yes, a full transcode is required. M4B only supports AAC, MP3, or FLAC audio, so AC-3, DTS, and LPCM streams found in Blu-ray M2TS files cannot be copied directly into the container. FFmpeg decodes the source audio and re-encodes it to AAC at the specified bitrate. This means there is a generation of lossy compression applied even if the source was lossless LPCM, so choosing a higher bitrate like 192k or 256k is advisable for high-fidelity source material.
Not automatically. Blu-ray chapter information is stored in external BDMV metadata files rather than inside the M2TS stream itself, so FFmpeg cannot read them during a simple file conversion. M4B chapters use QuickTime chapter track metadata, which must be added as a separate step using a tool like mp4chaps or by passing a chapter metadata file via FFmpeg's -map_metadata flag. The M4B container is fully capable of storing rich chapter data once it is supplied.
Replace the 128k value in the -b:a 128k flag with your preferred bitrate. For spoken-word content like audiobooks or lectures, 64k or 96k AAC is typically transparent and produces smaller files. For music, concert recordings, or high-fidelity source material from Blu-ray LPCM tracks, 192k or 256k is recommended to minimize perceptible quality loss during the transcode from a lossless source. The full adjusted flag would look like: ffmpeg -i input.m2ts -c:a aac -b:a 192k -movflags +faststart output.m4b
Yes. On Linux or macOS you can use a shell loop: for f in *.m2ts; do ffmpeg -i "$f" -c:a aac -b:a 128k -movflags +faststart "${f%.m2ts}.m4b"; done. On Windows PowerShell the equivalent is: Get-ChildItem *.m2ts | ForEach-Object { ffmpeg -i $_.FullName -c:a aac -b:a 128k -movflags +faststart ($_.BaseName + '.m4b') }. This is especially useful for processing a full Blu-ray disc's worth of M2TS segment files in a single operation.
M2TS files contain a full high-definition video stream — typically H.264 or H.265 at several megabits per second — plus multi-channel audio, which together can easily reach 20–50 GB for a full Blu-ray. The M4B output contains only a stereo AAC audio track at 128k bitrate, which is roughly 57 MB per hour of audio. Dropping the video stream alone accounts for the vast majority of the size reduction, with the AAC transcode adding a small additional reduction compared to lossless or high-bitrate source audio.
Technical Notes
M2TS files originating from Blu-ray discs often contain multi-channel audio (5.1 or 7.1) encoded as AC-3, E-AC-3, DTS-HD, or uncompressed LPCM. When FFmpeg re-encodes these to AAC for the M4B output, it defaults to downmixing to stereo unless you explicitly specify the channel layout with -ac. For audiobook use this is generally desirable, but for music or cinematic content you may want to retain surround channels if your playback device supports them — though most M4B-compatible players only handle stereo. The -movflags +faststart flag performs a second pass to move the moov atom to the start of the file, which is essential for streaming and for Apple Books to correctly recognize and bookmark the file. ID3-style metadata tags (title, author, album art) present in the M2TS — which are rare — are not reliably mapped to M4B's iTunes/QuickTime metadata fields by default; use -metadata title='...' flags or a post-processing tool like AtomicParsley to embed proper audiobook metadata. Note that M4B is effectively an AAC audio file in an MPEG-4 container with the extension renamed from .m4a — some players treat .m4a and .m4b identically, while Apple's ecosystem uses the .m4b extension specifically to enable bookmarking and chapter navigation features.