Convert AVCHD to MP4
AVCHD (Advanced Video Coding High Definition) is the recording format Sony and Panasonic camcorders have used since 2006. If you have footage from a Sony Handycam, a Panasonic HDC series, or an AVCHD Blu-ray, it's AVCHD - stored on the SD card as .mts files or transferred to disc as .m2ts files. The picture and sound inside (H.264 video with AC-3 or LPCM audio) are already what MP4 accepts, so Wave just changes the outer wrapper. No re-encoding, no quality loss, seconds to run. The output plays everywhere modern video plays - iPhones, browsers, smart TVs, uploads to social platforms.
What actually changes
AVCHD (Advanced Video Coding High Definition) is a recording format spec published jointly by Sony and Panasonic in 2006. It's a specific way of writing MPEG-2 Transport Streams (.mts or .m2ts file extensions) that carry H.264 video and AC-3 or LPCM audio, plus a directory structure on the SD card that camcorders use to organize clips (BDMV / PRIVATE / AVCHD folders with playlist and clip index files). What comes off your camcorder's card, when you look at it directly, is a folder tree with clips buried several levels deep - the actual video is in the STREAM/00001.MTS file, not somewhere sensible.
The conversion is a container swap - technically a "remux" (see Remux vs re-encode for what changes on each path). AVCHD stores H.264 at exactly the bitrates and profiles MP4 accepts, so Wave rewrites the container header (MPEG-TS to MP4), copies the video data through untouched, and converts the AC-3 or LPCM audio to AAC. MP4 technically accepts AC-3, but Chrome and Firefox play it as silence, so AAC is the safe choice. Zero video decoding, zero video re-encoding, seconds to run. If the container / codec distinction is unfamiliar, Codecs vs containers covers it.
The technical reason to convert: modern smart TVs, phones, browsers and upload sites expect MP4. AVCHD .mts files play in VLC and in the editors that grew up with them (Final Cut, Premiere, Vegas), but most phones, browsers and upload sites don't accept them. Windows Media Player has played AVCHD since Windows 7, though some files trip it up, and macOS's QuickTime Player won't open .mts files at all. The camcorder that recorded the file usually plays it back through its own screen or HDMI output, but off-camera playback is where the format falls down.
AVCHD Progressive (1080p60 recording added around 2011) and AVCHD 2.0 (3D and 4K in some cameras from 2012) both use the same underlying MTS/M2TS container with H.264 High Profile inside. Wave handles them identically - the codec/container relationship is the same; only bitrate and pixel dimensions differ. A 90-minute 1080p60 AVCHD recording is typically 25-40 GB (28 Mbps peak); the MP4 that comes out is essentially the same size because nothing gets re-encoded.
Three steps.
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Step 1
Copy the .mts or .m2ts file off the camcorder's SD card. It's inside the AVCHD/BDMV/STREAM folder, numbered like 00001.MTS.
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Step 2
Drop it onto Wave. Wave confirms the fast remux path.
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Step 3
Save the output MP4. The video and audio bytes are identical to the source; only the container header is rewritten.
Answers, specifically.
AVCHD vs MTS vs M2TS - what's the difference?
AVCHD is the recording format spec; MTS and M2TS are file extensions used by cameras that follow the spec. Sony camcorders typically use .m2ts; Panasonic often uses .mts. Contents are identical - MPEG-2 Transport Stream carrying H.264 + AC-3 or LPCM. Wave handles both identically.
The MP4 is the same size as the .mts. Bug?
No - that's expected. The video and audio streams are copied through untouched; only the container header rewrites. AVCHD is already H.264 in a transport stream, and MP4 accepts H.264 directly, so no re-encoding happens. Same size, same quality, different container.
AC-3 5.1 surround audio - does it survive?
Yes, as 5.1 AAC at 384 kbps. Wave converts the AC-3 track instead of copying it: AC-3 is legal inside MP4, but Chrome, Firefox and many Android players have no decoder for it and play the clip silent. AAC keeps all six channels and plays everywhere.
AVCHD 2.0 with 4K recording?
Yes. Same H.264 codec at a higher resolution. Wave handles 4K AVCHD identically to 1080p AVCHD - remux, no re-encode.
Chapter markers from the camcorder's "start recording" points?
AVCHD camcorders write chapter references into the playlist file (.mpl or .clpi), not into the .mts itself. Wave reads the raw .mts stream and doesn't currently import chapters from the playlist sidecars. Chapter preservation is on the roadmap; today's output has no chapter markers.
Multiple clips from a long recording (SD card split into 4 GB chunks) - can I merge them?
Not in the current build. AVCHD camcorders split recordings above 4 GB into consecutive .mts files (00001.MTS, 00002.MTS, etc.). Wave converts each separately; combining into one MP4 needs an editor or ffmpeg locally: `ffmpeg -f concat -safe 0 -i files.txt -c copy output.mp4`.
Timecode or GPS metadata from the camcorder - preserved?
Wave preserves the standard AVCHD metadata blocks that fit the MP4 container schema (creation date, camera model, coding parameters). Camcorder-specific extended metadata (per-clip GPS from GPS-equipped cameras, timecode tracks from some Sony pro camcorders) may not survive - some are container-level extensions MP4 has no home for.