mp4dump: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/mp4dump - from package: libmp4v2

You may install the required package with command yum install {package}

Error in other languages:
mp4dump: bevel nie gevind nie
mp4dump: comandă negăsită
mp4dump: comando não encontrado
mp4dump: commande introuvable
mp4dump: command not found
mp4dump: käsku ei ole
mp4dump: không tìm thấy lệnh
mp4dump: komanda nerasta
mp4dump: Kommando nicht gefunden.
mp4dump: kommandot finns inte
mp4dump: komut yok
mp4dump: nie znaleziono polecenia
mp4dump: níor aimsíodh an t-ordú
mp4dump: no se encontró la orden
mp4dump: no s'ha trobat l'ordre
mp4dump: opdracht niet gevonden
mp4dump: parancs nem található
mp4dump: perintah tidak ditemukan
mp4dump: príkaz nenájdený
mp4dump: příkaz nenalezen
mp4dump: команда не найдена
mp4dump: командата не е открита
mp4dump: 命令找不到
mp4dump: コマンドが見つかりません