1) Navegue para ACP --> Management --> Custom BBCode --> Add New BBCode


2) Preencha o formulário da seguinte maneira.

BBCode Title: YouTube
BBCode Description: : Use isso para incorporar um vídeo do YouTube
BBCode Example: VIDEO ID
BBCode Tag: youtube
Use Option in tag?: No
BBCode Replacement:
Código:
<object width="425" height="350"><param name="movie" value="http://www.youtube.com/v/{content}"></param><param name="wmode" value="transparent"></param><embed src="http://www.youtube.com/v/{content}" type="application/x-shockwave-flash" wmode="transparent" width="425" height="350"></embed></object>

Which groups can use this BBCode?:
All Current and future groups
Where can the BBCode be used?: Available in all sections

Depois de configurado clique em Add BBCode.