Most consumer cameras have a file size limit of 4 GB. If the recording is longer, it will be split into multiple parts. If you want to stabilize such split video, you'll have to merge the parts before stabilization. Gyroflow has a built-in tool to do that for you.
In case of GoPro files, it should detect the sequence automatically and ask you to merge the videos, when you load the first file from the sequence:
In case of all other cameras, you can simply drag & drop all files in your sequence to Gyroflow, and it will ask you if you want to merge them:
When joining video files from RunCam cameras, which have corresponding
.gcsvfiles with gyro data will also be automatically merged.