MTS files from a camcorder, and how to make them play

You copy footage off a Sony or Panasonic camcorder and get a folder of .MTS files that most software refuses to open. Nothing is broken. The camera recorded AVCHD, which is a camcorder standard rather than a delivery format, and the .MTS extension is the container it uses.

The video is already fine

This is the useful part. AVCHD stores H.264 video and AC-3 or PCM audio. H.264 is the same codec sitting inside almost every MP4 on the internet. Your player is not failing to decode the video, it is failing to read the container around it.

So the fix is to move the tracks into an MP4 container without touching them. No decoding, no re-encoding, no quality loss, and it finishes in seconds because the bytes are being copied rather than processed. Tools call this remuxing.

If a file will not play but the codec is supported, you need a container change, not a conversion.

Worth remembering

Copy the whole card, not just the clips

• AVCHD splits long recordings into separate .MTS files at around 2 GB each
• The folder structure holds the information about how those parts join up
• Dragging out only the .MTS files loses that, and long takes arrive in pieces
• Copy the entire AVCHD or PRIVATE folder off the card before you touch anything

When you do need a real conversion

Two cases. AC-3 audio is not universally supported on the web, so a clip headed for a browser may need its audio re-encoded to AAC while the video is still copied across untouched. And interlaced footage, which older camcorders produce, shows combing on fast movement. Deinterlacing changes every frame, so that one is a genuine re-encode with a genuine quality cost.

Everything else is a container swap. If a converter takes ten minutes on a five minute clip, it is re-encoding video that never needed it.