vp9_spatial_scalable_encoder: 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/vp9_spatial_scalable_encoder - from package: libvpx-utils

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

Error in other languages:
vp9_spatial_scalable_encoder: bevel nie gevind nie
vp9_spatial_scalable_encoder: comandă negăsită
vp9_spatial_scalable_encoder: comando não encontrado
vp9_spatial_scalable_encoder: commande introuvable
vp9_spatial_scalable_encoder: command not found
vp9_spatial_scalable_encoder: käsku ei ole
vp9_spatial_scalable_encoder: không tìm thấy lệnh
vp9_spatial_scalable_encoder: komanda nerasta
vp9_spatial_scalable_encoder: Kommando nicht gefunden.
vp9_spatial_scalable_encoder: kommandot finns inte
vp9_spatial_scalable_encoder: komut yok
vp9_spatial_scalable_encoder: nie znaleziono polecenia
vp9_spatial_scalable_encoder: níor aimsíodh an t-ordú
vp9_spatial_scalable_encoder: no se encontró la orden
vp9_spatial_scalable_encoder: no s'ha trobat l'ordre
vp9_spatial_scalable_encoder: opdracht niet gevonden
vp9_spatial_scalable_encoder: parancs nem található
vp9_spatial_scalable_encoder: perintah tidak ditemukan
vp9_spatial_scalable_encoder: príkaz nenájdený
vp9_spatial_scalable_encoder: příkaz nenalezen
vp9_spatial_scalable_encoder: команда не найдена
vp9_spatial_scalable_encoder: командата не е открита
vp9_spatial_scalable_encoder: 命令找不到
vp9_spatial_scalable_encoder: コマンドが見つかりません