It depends.
A video played in the Chrome browser (e.g. on youtube) actually allows this ("Cast this Tab").
A video played in the VLC or similar player locally: Unfortunately no, here Chromecast is used in the Chrome browser to stream "Cast Full Screen". However, this leads to poor quality and is not recommended.

We ourselves are waiting for Windows/macOS players like VLC or Quicktime to finally offer 100% Chromecast support. This would make it possible, but to my knowledge this is not "yet" the case.

Best regards