VLC does not support certain formats. I haven't dug into it, but I don't think it supports transcoding video to a chromecast endpoint either.
>If media codecs are supported by your Chromecast device, VLC only acts as a streaming server (which is battery consuming). If not, VLC will transcode and stream media, which is highly cpu and battery consuming.
[1] https://geoffreymetais.github.io/features/vlc-30/#chromecast