Webserver Chromecast Stream no sound

Hey guys,

I´m running a raspberry pi 3 with latest osmc and kodi software. I just enabled the webserver of osmc to use the Stream option.
My raspy is connected to a computer via hdmi (LAN to router) and I want to watch movies on my big tv with google chromecast (another room). So I opened the webserver on my smartphone (huawei p20 pro), open a movie and select “Stream”. The button itself works (opens a html5 player with streaming icon) and I also can see the video on my tv, but there is no sound. Of course the volume is up (smartphone, chromecast and tv).
Does anyone has a clue why? It´s just a normal mp4 file, nothing special…
Would be great if someone could help me out…

Regards johnny

Here’s a link to the formats Chromecast supports: https://developers.google.com/cast/docs/media

Might be that audio-format in that mp4 file isn’t supported by chromecast.