speexenc: 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/speexenc - from package: speex-tools

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

On Debian possible default full paths are:

/usr/bin/speexenc - from package: speex
/usr/lib/debug/usr/bin/speexenc - from package: libspeex-dbg

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