extract_a52: 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 Debian possible default full paths are:

/usr/bin/extract_a52 - from package: liba52-0.7.4-dev

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

Error in other languages:
extract_a52: bevel nie gevind nie
extract_a52: comandă negăsită
extract_a52: comando não encontrado
extract_a52: commande introuvable
extract_a52: command not found
extract_a52: käsku ei ole
extract_a52: không tìm thấy lệnh
extract_a52: komanda nerasta
extract_a52: Kommando nicht gefunden.
extract_a52: kommandot finns inte
extract_a52: komut yok
extract_a52: nie znaleziono polecenia
extract_a52: níor aimsíodh an t-ordú
extract_a52: no se encontró la orden
extract_a52: no s'ha trobat l'ordre
extract_a52: opdracht niet gevonden
extract_a52: parancs nem található
extract_a52: perintah tidak ditemukan
extract_a52: príkaz nenájdený
extract_a52: příkaz nenalezen
extract_a52: команда не найдена
extract_a52: командата не е открита
extract_a52: 命令找不到
extract_a52: コマンドが見つかりません