Convert MTS to M4B — Free Online Tool
Convert MTS camcorder footage to M4B audiobook format by stripping the H.264 video and re-encoding the AC-3 or AAC audio track into a chapter-aware MPEG-4 audio file. This is ideal for extracting narration, interviews, or spoken content recorded on Sony or Panasonic AVCHD cameras and repurposing it as a bookmarkable audiobook or podcast episode.
to
FFmpeg Command
Copy this command to run the same conversion locally with FFmpeg on your desktop. Download FFmpeg
Drop your MTS file here
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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 are AVCHD containers carrying H.264 video and either AC-3 or AAC audio, recorded directly by Sony and Panasonic camcorders. M4B is an audio-only MPEG-4 container that supports chapters and bookmarking but carries no video stream. During this conversion, the video stream is discarded entirely — there is no video re-encoding. The audio stream is decoded from its original AC-3 or AAC encoding and re-encoded to AAC at 128k bitrate, then wrapped in an MPEG-4 container with the +faststart flag applied. The +faststart flag moves the MOOV atom to the beginning of the file, enabling progressive playback in podcast apps and audiobook players like Apple Books before the full file has loaded.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg command-line tool, which is running here as a WebAssembly (FFmpeg.wasm) instance entirely inside your browser — no files leave your machine. |
-i input.mts
|
Specifies the input AVCHD MTS file from your Sony or Panasonic camcorder. FFmpeg reads the MPEG-2 Transport Stream container and identifies the H.264 video and AC-3 or AAC audio streams inside. |
-c:a aac
|
Encodes the output audio stream using FFmpeg's native AAC encoder. This is required because M4B only supports AAC audio — any AC-3 audio from Panasonic AVCHD recordings must be transcoded, and even existing AAC audio is re-encoded to ensure clean M4B container compatibility. |
-b:a 128k
|
Sets the AAC audio bitrate to 128 kilobits per second. For spoken word content like narration or interviews extracted from camcorder footage, 128k AAC provides clean, clear audio while keeping the M4B file size manageable. |
-movflags +faststart
|
Moves the MOOV atom (the file's index and metadata block) from the end of the M4B file to the beginning. This is essential for podcast and audiobook distribution, as it allows Apple Books, Overcast, and other players to begin playback before the entire file has finished downloading. |
output.m4b
|
Specifies the output filename with the .m4b extension. The .m4b extension is what signals to Apple Books, iTunes, and podcast apps that this MPEG-4 audio file supports chapter navigation and playback bookmarking — a plain .m4a file with the same content would not trigger these features in many players. |
Common Use Cases
- Extract spoken narration or commentary recorded on a Sony or Panasonic AVCHD camcorder and publish it as a bookmarkable audiobook episode in Apple Books
- Convert a recorded lecture or presentation filmed on an AVCHD camcorder to M4B so students can listen on the go and resume playback from where they left off
- Pull the audio interview track from a multi-hour MTS recording and package it as a podcast episode in M4B format with chapter support
- Archive fieldwork audio notes recorded on a Panasonic HC-series camcorder into a portable M4B file that supports bookmarking for later reference
- Convert MTS footage of a walking tour or guided event to M4B so the audio commentary can be distributed as a self-guided audiobook experience
- Strip the video from a training video recorded in AVCHD format and deliver the instructional audio as an M4B file compatible with Apple Podcasts and Overcast
Frequently Asked Questions
The AC-3 audio from your MTS file is always re-encoded — it cannot be copied directly into an M4B container because M4B is an MPEG-4 format that only supports AAC, MP3, or FLAC audio. FFmpeg decodes the AC-3 track and re-encodes it to AAC at 128k bitrate. If your MTS file already contains an AAC audio track, it is still re-encoded rather than stream-copied, because the M4B container's requirements and the +faststart flag necessitate a full mux pass.
M4B is a purely audio format — it is an MPEG-4 container variant specifically designed for audiobooks and podcasts, and it does not support video streams. The H.264 video recorded by your camcorder is intentionally discarded during this conversion. If you need to keep the video, you should convert your MTS file to a video format like MP4 instead.
M4B natively supports chapters, which is one of its key advantages over plain M4A or MP3 files. However, the FFmpeg command shown here does not automatically generate chapter markers from an MTS source, since AVCHD recordings do not typically embed chapter metadata. To add chapters, you would need to supply a chapter metadata file using FFmpeg's -i flag with a metadata text file, or use a dedicated audiobook tool like Chaptered or mp4chaps after conversion.
Adjust the -b:a flag to change the AAC audio bitrate. For example, replace 128k with 192k for higher quality speech or 96k to reduce file size for voice-only content. For audiobooks and spoken word recordings from a camcorder, 96k to 128k AAC is generally sufficient, as the human voice doesn't benefit significantly from higher bitrates. The full adjusted command would look like: ffmpeg -i input.mts -c:a aac -b:a 192k -movflags +faststart output.m4b
AVCHD MTS files embed minimal metadata in their transport stream headers, including timestamps and sometimes GPS data depending on the camcorder model. This metadata is largely incompatible with the ID3-style tags used in M4B files and is not carried over automatically by FFmpeg. If you need to embed audiobook metadata such as title, author, or album art into the M4B, you should use FFmpeg's -metadata flag to set these values explicitly during conversion.
The browser-based tool supports files up to 1GB processed entirely locally without any upload. For MTS files exceeding 1GB — which is common for longer AVCHD recordings since MTS files span at 2GB boundaries on camcorder memory cards — you can copy the exact FFmpeg command shown on this page and run it directly on your desktop with FFmpeg installed. The command is identical; desktop FFmpeg has no file size limit and will typically process large MTS files faster than the browser-based version.
Technical Notes
MTS files from Sony and Panasonic AVCHD camcorders use MPEG-2 Transport Stream packaging with H.264 video and either Dolby Digital AC-3 (common on Panasonic models) or AAC audio (common on Sony models). M4B uses the MPEG-4 Part 14 container — the same underlying structure as MP4 and M4A — but with the .m4b extension signaling chapter and bookmark support to audiobook-aware players. Because M4B supports only AAC, MP3, or FLAC audio, any AC-3 audio from AVCHD must be transcoded, introducing a generation of lossy re-encoding. Starting from a well-recorded camcorder source at typical AC-3 bitrates of 192–256k and targeting AAC at 128k, the quality loss for spoken word content is minimal and generally imperceptible. The -movflags +faststart flag is particularly important for M4B files distributed as podcasts, as it repositions the file's index data to the front of the file, allowing podcast apps to begin playback during download. Note that AVCHD recordings spanning multiple 2GB MTS segment files (recorded continuously) are not automatically joined by this tool — each segment must be converted individually or concatenated first using FFmpeg's concat demuxer.