Video
Convert MTS and AVCHD to MP4 on Mac
To convert MTS to MP4 on a Mac, run ffmpeg -i in.mts -c:v copy -c:a aac out.mp4. It rewraps the video without re-encoding it. Apple’s built-in avconvert also reads MTS. Smol does not: it rejected my .mts file outright.
How do I open an AVCHD card or folder on a Mac?
Camcorders from Sony, Panasonic, Canon and others record AVCHD: a folder structure that Finder shows as a single file with an .avchd extension (a package). The actual video lives inside it as .mts or .m2ts files.
- Copy the whole card or the AVCHD folder to your Mac. Do not copy single files out of it.
- Control-click the .avchd item in Finder and choose Show Package Contents.
- Open BDMV, then STREAM. The clips are the numbered .mts files there, such as 00001.MTS.
Copy those files to a normal folder before converting. Importing straight from the camera through Photos or iMovie also works, but that locks the footage into a library.
How do I convert MTS to MP4 on a Mac?
Install ffmpeg once, then rewrap each clip:
brew install ffmpeg
ffmpeg -i 00001.MTS -c:v copy -c:a aac clip.mp4AVCHD video is H.264, which MP4 holds as is, so -c:v copy skips the slow part. Camcorders usually record AC-3 audio, which is why the command converts audio to AAC. My test file had the same H.264 and AC-3 pairing. The result was a 114,096 byte MP4 from a 164,688 byte .mts, in under a second.
A whole card in one go:
for f in *.MTS; do ffmpeg -i "$f" -c:v copy -c:a aac "${f%.MTS}.mp4"; doneInterlaced footage (1080i) stays interlaced after a copy, and some players show combing. If that bothers you, you need a re-encode with a deinterlace filter instead of a copy.
Can I use a built-in Mac tool?
Yes. avconvert accepted my .mts file and rewrapped it with no re-encode:
avconvert --preset PresetPassthrough --source 00001.MTS --output clip.movThat produced a 127,024 byte MOV from the 164,688 byte source, and it is free and already installed. It keeps the camcorder’s audio as it is, so a few apps may not like AC-3 inside MOV. QuickTime Player can open some MTS files directly, but support varies by camera, so test one clip first. This was a generated test stream, not a card from a real camcorder.
Can Smol convert MTS or AVCHD?
Not directly. I asked Smol 1.0.35 to convert my .mts file to MP4 and it failed with the message “.mts files can’t be converted.” Smol reads AVI, MP4, MOV, WebM and MKV for video, but not MTS.
The workaround is a two-step job. Rewrap the clips to MOV with avconvert first, then give the MOV files to Smol to compress or convert. I tried that: Smol accepted the rewrapped MOV and ran a compress on it. Because the clips are already efficient H.264, expect small savings, and Smol may leave a file alone when it cannot make it smaller. See compressing video on a Mac for realistic numbers.
Which MTS method should I pick?
| Method | Reads .mts | Re-encodes | Result on test clip |
|---|---|---|---|
| ffmpeg copy video, AAC audio | Yes | Audio only | 114,096 byte MP4 |
| avconvert passthrough | Yes | No | 127,024 byte MOV |
| VLC (File > Convert / Stream) | Yes | Yes | Not measured |
| Smol | No | n/a | Rejected the file |
When is Smol the wrong tool for this?
Here, it is the wrong tool for the first step. Smol cannot read MTS, so use ffmpeg or avconvert for the conversion. Both are free and keep the picture untouched. VLC will also play the raw .mts files if you only need to watch them (see VLC alternatives for Mac).
Smol earns its $29 afterward, when a folder of finished MP4 or MOV clips needs shrinking for email or upload, from the Finder, with nothing leaving your Mac: see Smol. For other conversions, read the best file converters for Mac and the best video compressor for Mac.
How we checked this
Generated a 5 second 720p H.264/AC-3 transport stream named .mts, converted it with ffmpeg, avconvert and Smol 1.0.35, and checked codecs with ffprobe. Not a real camcorder card. Facts last checked . We make Smol, so treat our claims about it with the same care as any vendor’s, and see our editorial policy.
MTS and AVCHD: common questions
What is an MTS file?
An MTS file is an MPEG transport stream clip recorded by AVCHD camcorders. It usually holds H.264 video and AC-3 audio. The camera stores the clips in a BDMV/STREAM folder inside an AVCHD package, which is why you often find them numbered like 00001.MTS.
Does converting MTS to MP4 lose quality?
Not if the video is copied. AVCHD already uses H.264, so ffmpeg’s -c:v copy moves it into MP4 untouched. Only the audio is converted, from AC-3 to AAC. Any re-encode, such as to shrink the file, does lose a small amount of detail.
Can QuickTime Player open MTS files on a Mac?
Sometimes. macOS recognizes MTS as AVCHD, and avconvert read my test file, but QuickTime support varies by camera and audio format. Try one clip. If it will not play, rewrap it to MP4 with ffmpeg or play it in VLC.
Can Smol open MTS files?
No. Smol 1.0.35 rejected my .mts file with “.mts files can’t be converted.” Rewrap the clip to MP4 or MOV first with ffmpeg or avconvert, then Smol can work on the result. It reads AVI, MP4, MOV, WebM and MKV for video.
Why does my AVCHD card show as one file?
Finder treats the AVCHD folder as a package so it looks like a single item. Control-click it and choose Show Package Contents, then open BDMV and STREAM to see the individual .mts clips. Copy the whole card first, never single files.
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