Convert MTS (and M2TS) to MP4
MTS and M2TS are the AVCHD camcorder format - Sony Handycams, Panasonic camcorders, and AVCHD Blu-ray discs record into it. Inside is almost always H.264 video with AC-3 audio, which MP4 accepts directly. Wave repackages the streams without re-encoding.
What actually changes
MTS and M2TS are the same container - MPEG-2 Transport Stream wrapped in BDAV, the AVCHD variant Sony and Panasonic standardised on around 2006 for consumer camcorders. The extension differs by tool: cameras record .mts on the SD card, Blu-ray-authored discs and PC-side tools use .m2ts. Wave treats them identically.
Because the payload is H.264 video plus AC-3 or LPCM audio, MP4 accepts almost everything. When the audio is AC-3, the conversion is a pure re-mux - every byte of video and audio is copied bit-for-bit, and the container index is rebuilt for fast-start playback. When the audio is LPCM (some older Panasonic camcorders, some AVCHD Blu-ray tracks), the audio re-encodes to AAC at 192 kbps because MP4 doesn't carry PCM in a broadly-playable way. Video always copies through.
Three steps.
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Step 1
Drop your .mts or .m2ts file onto the card.
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Step 2
Wave inspects the streams and shows Fast copy for the video track. Audio may need a quick re-encode if it's LPCM.
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Step 3
Convert and save the MP4.
Answers, specifically.
Why not just rename .mts to .mp4?
Because MTS is a transport stream inside - different packet structure, no MP4-style index. Players that trust the extension will crash or refuse the file. A real remux rewrites the container and builds an MP4 index, without touching the video pixels or audio samples.
My camcorder splits long recordings into 4 GB chunks. Can Wave stitch them?
Not automatically in the current build. Concatenate the chunks yourself first (any AVCHD-aware tool, or ffmpeg concat), then drop the joined file onto Wave for the remux to MP4.
Do subtitle or chapter tracks come across?
AVCHD MTS files rarely carry text subtitles; when they do, Wave preserves them. Chapter markers from AVCHD discs pass through as MP4 chapter atoms.
What about 4K MTS from newer camcorders?
4K H.264 (60p, high bitrate) remuxes cleanly. Very large files (over 4–5 GB per clip) push against browser memory even for a pure remux - Wave warns above 2 GB and the ceiling is 8 GB per file.
Will the file get smaller?
Typically slightly smaller. AVCHD transport-stream packaging adds a few percent of overhead that MP4's tighter container structure sheds. The picture and sound are identical.