mpeg2vldemo: 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 CentOS possible default full paths are:

/usr/bin/mpeg2vldemo - from package: libva-utils

You may install the required package with command yum install {package}
Error in other languages:
mpeg2vldemo: bevel nie gevind nie
mpeg2vldemo: comandă negăsită
mpeg2vldemo: comando não encontrado
mpeg2vldemo: commande introuvable
mpeg2vldemo: command not found
mpeg2vldemo: käsku ei ole
mpeg2vldemo: không tìm thấy lệnh
mpeg2vldemo: komanda nerasta
mpeg2vldemo: Kommando nicht gefunden.
mpeg2vldemo: kommandot finns inte
mpeg2vldemo: komut yok
mpeg2vldemo: nie znaleziono polecenia
mpeg2vldemo: níor aimsíodh an t-ordú
mpeg2vldemo: no se encontró la orden
mpeg2vldemo: no s'ha trobat l'ordre
mpeg2vldemo: opdracht niet gevonden
mpeg2vldemo: parancs nem található
mpeg2vldemo: perintah tidak ditemukan
mpeg2vldemo: príkaz nenájdený
mpeg2vldemo: příkaz nenalezen
mpeg2vldemo: команда не найдена
mpeg2vldemo: командата не е открита
mpeg2vldemo: 命令找不到
mpeg2vldemo: コマンドが見つかりません