avprobe: command not found

Have You tried accessing the binary with the full path?

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 Debian possible default full paths are:

/usr/bin/avprobe - from package: libav-tools

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