width and height adjustments on only youtube iframes


Staff member
how to make adjustments on width and height for all youtube embeds only, because there are some iframes that is used and mostly are youtubes

<iframe width="420" height="315" frameborder="0" allowfullscreen="" src="http://www.youtube.com/embed/xbGv2T456dfg3">

this codes is embedded in my wordpress post, I want to adjust the width and height for only youtube iframes and not all iframes, I can adjust manually but when it comes to many videos then it will be long to do.

for example
* all youtube iframes will be 560x316
* and all other iframes will be its default dimension.

can it be done in php? sorry Im new