Not casting to Chromecast

[fancy]

Hello everyone,
I have a problem using chromecast on my MacBook Air : when I launch a video on VLC, only the images of the video are displayed on the TV, but the sound comes out from my computer. So I tried I tried to slide my video on Chrome but no sound appears, the sound icon is grayed out... I contacted the google assistance that told me Apple forbid Chromecast to take control of the sound of the Mac's desktop, but with the sound of Chrome it normally works which is not the case here... Do you know how to fix my problem please ?