ffmpeg merge multiple streams

• [ffmpeg merge]

ffmpeg -i input1.mkv -i input2.webm -i input3.mov \
-filter_complex '[0:v:0][0:a:0][1:v:0][1:a:0][2:v:0][2:a:0]concat=n=3:v=1:a=1[outv][outa]' \
-map '[outv]' -map '[outa]' output.mp4

• See also [ffmpeg – Merge two video clips into one | Unix & Linux Stack Exchange
  ]

  ffmpeg \
    -i input1.mp4 \
    -i input2.mp4 \
    -filter_complex '[0:v]pad=iw*2:ih[int];[int][1:v]overlay=W/2:0[vid]' \
    -map [vid] \
    -c:v libx264 \
    -crf 23 \
    -preset veryfast \
    output.mp4