MTS to M4B Converter

Convert MTS to M4B Online

MTS is the AVCHD video format your camcorder writes; M4B is Apple's audiobook container. This converter pulls the audio track out of an MTS recording and wraps it as an .m4b file, so a lecture, sermon, talk, or interview you filmed on a camcorder opens in Apple Books and other audiobook apps with their resume-position feature. The video is discarded — only the soundtrack is kept.

What MTS (AVCHD) Audio Looks Like

What M4B Is — and What It Doesn't Do

The single most important thing to understand: converting one MTS file to M4B produces one continuous track, not a chaptered audiobook. A two-hour recording becomes a two-hour file with a single implied chapter. Chapter markers — the kind that let you jump between sections — have to be authored in a dedicated audiobook tool (for example Audiobook Binder on Mac); no format conversion can invent them from a plain recording. What you do get for free is the .m4b extension's resume behavior, which is the feature most people actually want: close the app, reopen days later, and an audiobook player picks up exactly where you stopped.

How to Convert MTS to M4B

1. Upload Your MTS File: Drag and drop the .mts onto the page or click "Add Files." Long recordings are large, so the main wait is the upload finishing.
2. Set the Bitrate under File Compression: The panel opens on the Quality Preset dropdown, the hands-off mode — nothing is pre-selected in it, so leaving it alone hands the server its own default rather than the label on screen, and it is the least predictable control here. For a result you can plan around, switch to Custom Bitrate and type 64 kbps for narration or 96–128 kbps if there is music or a full room of speakers, or use Constant Bitrate, whose ladder runs 8 to 384 kbps and opens on 128 kbps.
3. Set Audio Channel and Sample Rate (Optional): Leave Audio Channel on Original, or choose Mono to roughly halve the size of a single-speaker recording. Leave Audio Sample Rate on Original; AVCHD audio is already capped at 48 kHz, so raising it adds nothing.
4. Convert and Download: Click Convert and save the .m4b. No sign-up, no watermark.

Frequently Asked Questions

Does converting MTS to M4B create chapters automatically?

No. A format conversion turns one MTS recording into one continuous .m4b track — a two-hour talk becomes a two-hour file with no chapter breaks. The M4B container can hold chapter markers, but they have to be authored deliberately in an audiobook-building tool; nothing about converting a single file generates them. What the .m4b extension does give you automatically is resume-position support in Apple Books and other audiobook players, which is usually the real reason to pick this format over a plain audio file.

What is the difference between M4B and M4A here?

Almost nothing technical — both wrap AAC audio in an MPEG-4 container, and the bytes of the audio are identical. The only real difference is the extension: .m4b tells audiobook apps to treat the file as a book and save where you stopped, while .m4a is treated as a regular music track with no global resume point. If you want the resume/bookmark behavior, use this page; if you just want plain AAC audio for a music library, MTS to M4A produces the same audio with the music-style extension.

Will I lose quality converting AVCHD audio to M4B?

It depends on the camcorder's audio codec. Most consumer AVCHD cameras record Dolby Digital (AC-3), which is already lossy; re-encoding that to AAC is a lossy-to-lossy step, so it cannot recover detail and a low output bitrate will degrade it further — keep the bitrate at or above the source. Higher-end models record uncompressed LPCM, and encoding that to AAC is a clean first-generation compression with no earlier loss to compound. For spoken word the difference is rarely audible at 64 kbps or above.

What bitrate should I use for a recorded lecture or talk?

For a single speaker, 64 kbps is the long-standing voice default — it keeps a multi-hour file manageable without audible harm to speech. Step up to 96–128 kbps if the recording has music, audience sound, or several voices, where the extra bits help. In our testing, a one-hour single-speaker MTS recording exported at 64 kbps mono produced an M4B of roughly 28–30 MB.

Can I keep the video instead of just the audio?

Not with this tool — converting MTS to M4B discards the picture by design, because M4B is an audio-only container. If you want to keep the footage in a widely playable format, use MTS to MP4 instead. If you only need plain audio and don't care about the audiobook resume feature, MTS to MP3 is the most universally compatible target.

How do I add chapter markers to the M4B afterward?

Because a format conversion can't invent chapters, you add them in a dedicated audiobook tool after downloading. On a Mac, Audiobook Binder can import the audio and let you place chapter marks; cross-platform, the open-source m4b-tool builds a chaptered .m4b from marker timestamps. You define where each section begins, and the tool writes those markers into the container so players show a chapter list.

Will the M4B resume where I left off on another device?

The resume behavior comes from the .m4b extension telling the player to remember your position, and Apple Books syncs that position across your devices through iCloud when Books syncing is turned on — so you can stop on an iPhone and pick up on an iPad or Mac.

The position is stored by the player, not inside the file itself, so a different app (or a device not signed into your iCloud) starts its own bookmark. If cross-device resume matters, keep the audiobook in one player's library rather than copying the raw file around.

How are my uploaded recordings handled?

Files are uploaded over an encrypted connection, processed on our servers, and deleted automatically a few hours after conversion. There is no sign-up, no watermark, and your files are never shared or made public. With a long recording, the main wait is upload and encode time, which scale with the length of the file rather than any per-file size cap.