Many AVCHD video cameras write large video in many MTS fragments. For example, there are typical flash card files from a Sony NEX camera:
00123.MTS 1905 MB 00124.MTS 2026 MB 00125.MTS 2026 MB 00126.MTS 783 MB 00127.MTS 2003 MB
Here 00125.MTS, 00126.MTS and 00127.MTS are parts of the same recording session: the first two files have the same size 2 GB.
To use these spans in any video editor or media player you should join them together.
Use a Windows batch command:
copy /b 00125.MTS + 00126.MTS + 00127.MTS out.mts
In some cases this way may not work, so use next methods:
ffmpeg.exe -i "concat:00125.MTS|00126.MTS|00127.MTS" -vcodec copy -acodec ac3 -sn out.mov
AC3 is not supported by DaVinci Resolve before version 14, so you can use next method:
ffmpeg.exe -i "concat:00125.MTS|00126.MTS|00127.MTS" -vcodec copy -acodec pcm_s16be -sn out.mov
Please note that very long sequences may not be placed in MOV container. You can try MKV instead. Or make MP4 with a near-lossless AAC encoding:
ffmpeg.exe -i "concat:00125.MTS|00126.MTS|00127.MTS" -vcodec copy -acodec aac -ab 512k -cutoff 22050 -sn out.mp4
Please note that AAC encoder from FFmpeg has very poor quality, so we use 512k. You can try 320k or less if your audio record is not important. For old FFmpeg versions add -strict experimental.
Extended editions of Video Artifact can automatically join MTS files when importing. They can find all required spans automatically. But a manual joining is required if you use the Basic edition.
Steps to get spans joined are:
Place all MTS spans to the project folder.
Execute import script related to your camera model from va\import\Generic\camera-manufacturer\camera-model.bat.
Get the result in the src/ folder.