#!/bin/bash
filesList=""
for file in $(ls *.mp4|sort -n);do
filesList="$filesList -cat $file"
done
MP4Box $filesList -new merged_files_$(date +%Y%m%d_%H%M%S).mp4
для MP4Box по этой ссылке https://askubuntu.com/questions/122447/best-command-line-tool-to-join-videos/1116505#1116505