speexdec: 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/speexdec - from package: speex-tools

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

On Debian possible default full paths are:

/usr/bin/speexdec - from package: speex

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

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