How to join (merge or concatenate) video files

join files by avconv

avconv  -i concat:file1.mp4\|file2.mp4\|file3.mp4\|file4.mp4

example

avconv -i concat:file1.mp4\|file2.mp4 -c copy output.mp4

join files by mencoder

mencoder -oac copy -ovc copy video1.mp4 video2.mp4 -o output.mp4

mencoder -oac pcm -ovc copy video.mp4 video.mp4 video.mp4 -o output.mp4