- Make sure the router is close to your Chromecast and computer
- Plug your computer into your router with an ethernet cable
- Reboot your router and Chromecast by unplugging them and plugging them back in
- Make sure your router has Multicast and SSDP enabled
- Use the HDMI extender that came with your Chromecast (sometimes your TV throws of network interference that the extension can protect your Chromecast from)
- Make sure no one on your network is doing anything heavy (downloading, Netflix, Youtube...)
- Do you live in an apartment building or near lots of other neighbours (and their routers)? Sometimes Wifi interference can be a big issue, try using this app (https://play.google.com/store/apps/details?id=com.farproc.wifi.analyzer&hl=en) to see if your network is running on the same channel as a lot of other local networks. If so, then changing to a less used channel may help a lot!
- Try watching an MP4 file, since those usually don't need to be converted