/var/www/bin/ffmpeg -i "videologo/999999_second_stage.mp4" -i "output.mp4" -i "outros/final-outro.mp4" -filter_complex "[0:v] [0:a] [1:v] [1:a] [2:v] [2:a] concat=n=3:v=1:a=1: "[v]" "[a]"" -map '[v]' -map '[a]' -vcodec libx264 output3.mp4


Stream specifier ':a' in filtergraph description [0:v] [0:a] [1:v] [1:a] [2:v] [2:a] concat=n=3:v=1:a=1 [v] [a] matches no streams.