vpxdec: 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/vpxdec - from package: libvpx-utils

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

On Debian possible default full paths are:

/usr/bin/vpxdec - from package: vpx-tools

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

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