You can use ffmpeg for this concatenating movies. First check if you have ffmpeg installed by running ffmpeg
. If the first line ends with "the FFmpeg developers", you're fine. If it is "the Libav developers", then ffmpeg is secretly an alias to avconv (this is the case on Ubuntu). If you don't have ffmpeg and the real ffmpeg is not in your repository, you have to compile ffmpeg yourself.
Now that you have the real ffmpeg, create the file inputs.txt with the following text:
file 1.flv
file 2.flv
file 3.flv
and run:
ffmpeg -f concat -i inputs.txt -c copy result.flv