Manatee

How to convert MTS or M2TS camcorder video to MP4 on a Mac

· 6 min read

MTS and M2TS files come from AVCHD camcorders, and the video inside them is almost always plain H.264, which every Mac can play. The problem is the wrapper: a transport stream that QuickTime does not understand, usually carrying Dolby Digital audio that MP4 players do not expect. Converting to MP4 means moving the video into a friendlier container and re-encoding the audio, which Manatee does by drag and drop, and which iMovie or a Finder quick action can do if your Mac is able to read the file at all.

What an MTS file actually is

AVCHD was the recording format of most consumer and prosumer camcorders sold from the late 2000s through the 2010s. The camera writes an MPEG-2 transport stream with the extension .MTS into a folder tree on the memory card (PRIVATE/AVCHD/BDMV/STREAM). When transfer software copies those clips to a computer it often renames them .m2ts; the two extensions describe the same thing.

Inside the stream there are two tracks: H.264 video, often 1920x1080 and often interlaced (1080i), and audio that is usually Dolby Digital (AC-3), occasionally uncompressed PCM on higher-end models. This matters because the video needs no real conversion, only a new container, while the audio generally does need converting, because AC-3 inside an MP4 file is not something QuickTime Player, Photos, or most phones will play. If you have ever wondered why a video plays on one Mac and not another, container vs codec is the whole story.

Copy the files off the card first

Work from a copy on your internal drive, never from the card directly.

  1. Put the card in a reader (or connect the camcorder by USB) and open it in Finder.
  2. Copy the entire PRIVATE folder to your Mac. Keeping the structure intact is useful if you later want iMovie to import the footage as a set.
  3. Look in BDMV/STREAM for the .MTS files. They are numbered 00000.MTS, 00001.MTS and so on.
  4. Notice any recordings that span consecutive numbers. Memory cards formatted as FAT32 cannot hold a file over 4 GB, so the camcorder silently splits a long recording into several sequential files. None of the methods below joins them; you will get one MP4 per file, and a video editor is the tool for stitching them back together.

Copying is also the point where files get damaged. If a clip copies as a suspiciously round size or refuses to play after transfer, read file transfer interrupted: how to salvage a half-copied video before converting anything.

Convert with Manatee

Manatee accepts both .mts and .m2ts among its 122 input types and writes MP4 as one of its conversion targets. It bundles its own conversion engine, so it does not depend on whether macOS can decode the file.

  1. Open Manatee. It is free with every feature for 24 hours, with no account or card required, then $9 once.
  2. Drag the .MTS files onto the menu bar icon or into the window’s drop zone. You can drop a whole STREAM folder’s worth at once; each file becomes a job in the list.
  3. Choose Convert and pick MP4.
  4. Wait for the job list to finish. Each MP4 is written next to the original, and the original is never modified.

The MP4 that comes out plays in QuickTime Player, imports into Photos, and sends through Messages or AirDrop without complaint. If you need the file smaller than the camcorder’s original bitrate produced (AVCHD clips run to around 200 MB per minute at the highest settings), run the MP4 through Manatee’s Shrink mode afterward and name the size you want. Do the shrink from the freshly converted file rather than converting and shrinking repeatedly; compressing twice always costs quality.

Manatee is not a video editor. It will not deinterlace, trim, color-correct, or join split clips. It converts what is in the file.

Convert with what is already on your Mac

Whether these work depends on your Mac’s version of macOS and the particular camcorder’s flavor of AVCHD. Try them in this order.

Finder quick action. Select the .MTS file, right-click, choose Quick Actions, then Encode Selected Video Files. Pick 1080p (or the clip’s native size) and click Continue. If the option is missing or the encode fails immediately, macOS cannot read the stream and you will need Manatee or iMovie. The result may carry an .m4v extension, which is an MP4 in everything but name; renaming it to .mp4 is safe.

iMovie. Choose File, then Import Media, and navigate to the PRIVATE folder you copied. iMovie recognizes the AVCHD structure and lists the clips by thumbnail. Import them, drop them in a project, then File, Share, File to export an MP4. This route works for almost every AVCHD camcorder but makes you create a project and re-encodes the footage on the way out.

QuickTime Player. Recent versions of macOS can open some .MTS files directly. If yours opens, File, Export As, 1080p produces a .mov, not an MP4. For most purposes that is just as good; the two containers hold the same video, and nearly everything that plays one plays the other.

Interlacing and what to expect from quality

Many AVCHD camcorders recorded 1080i, which is interlaced: each frame is two half-frames captured a fraction of a second apart. Played on a computer screen, fast motion shows a comb pattern at the edges. Converting to MP4 does not cause this and does not cure it; the interlacing was in the original. If combing bothers you, import through iMovie or another editor that deinterlaces during import, then export from there.

Aside from interlacing, a conversion at the source resolution should look indistinguishable from the original on any normal screen. The camcorder’s H.264 was already a decent encode, and a conversion that keeps the resolution and frame rate has nothing to gain by discarding detail. Dolby Digital to AAC is not a change you will hear on camcorder sound.

If the file will not convert at all

A clip that every tool rejects is usually damaged rather than merely unusual. Camcorders are hard on files: batteries die mid-recording, cards get pulled early, and the index at the end of the stream never gets written. Manatee’s Repair mode handles this case. Drop the file, choose Repair, and it reports one of three outcomes: Fixed, Partial (for instance, the first eleven minutes of a fourteen-minute clip), or Not fixable. Data that was never written cannot be recovered, and Manatee will say so rather than hand you a file that looks whole and is not.

To diagnose before you repair, see how to check whether a video file is corrupted on a Mac.

Questions

Is M2TS the same as MTS?

Yes. Both are MPEG-2 transport streams carrying H.264 video. The camcorder writes .MTS because the card’s file system limits names to eight characters and a three-letter extension; software that copies the clips to a computer often expands it to .m2ts. Any converter that takes one takes the other.

Can I just rename the file from .mts to .mp4?

No. The extension is a label, not the container. A renamed file will either refuse to open or play video with no sound, depending on the player. Convert it properly.

Why does the AVCHD folder look like a single file on my Mac?

Finder shows the AVCHD folder as a package. Right-click it and choose Show Package Contents, then open BDMV and STREAM to reach the .MTS files inside.

Will the MP4 be bigger or smaller than the MTS?

Roughly similar, because the output keeps the source resolution and frame rate. If you need it smaller, that is a separate step: convert first, then use Shrink on the MP4 and name the size.