In this post will be described how to use FFmpeg to Concatenate the multiple images, multiple videos convert to a video.   If you have 2 JPG images and would like to Concatenate into a single JPG file with make size 500X500 use the command as below,

$ sudo ffmpeg -loop 1 -i concat:"image1.jpg|image2.jpg" -s 500X500 -c copy thelinuxfaq.jpg

Second one is multiple audio files(format .mp3) and use single image file convert to .mp4 video file. 

$ sudo ffmpeg -loop 1 -i thelinuxfaq.jpg -i concat:"audio_file1.mp3|audio_file2.mp3|audio_file3.mp3" -c:a copy -c:v libx264 -shortest output_video.mp4

You should be able to use the concat protocol method to combine the files:

$ sudo ffmpeg -i "concat:input_video1.mp4|input_video2.mp4|input_video3.mp4" -c copy output_video.mp4​