monline

Many video recorders (eg. GoPro cameras and many phones) split video files into 2 (or 4) GB pieces. To concatenate these pieces into a single file (without reencoding them), you can use ffmpeg's "concatenate" demuxer:

P.S.: of course to do this, you need to run ffmpeg on a filesystem that supports files with larger than 4 GB files (i.e. not fat or fat32, but something better ... like HFS+ for Macs or ExFAT for Windows or ext2/ext3/ext4 (etc.) for Linux).