mediainfo-gui: 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/mediainfo-gui - from package: mediainfo-gui

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

On Debian possible default full paths are:

/usr/bin/mediainfo-gui - from package: mediainfo-gui

You may install the required package with command apt-get install {package}

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