This is a known, memory-related issue with Chromecast 1st & 2nd generation. When you play your content at a very high bitrate, the Chromecast Default Media Receiver can sometimes run out of memory available to it, which can either result in freezing or poor playback experience (it may manifest as buffering).
In this case, you can fix the problem by following the steps below:
Disconnect your Chromecast from the app.
Open the Elmedia Player Preferences. Go to the Streaming tab and decrease the video quality and/or bitrate.
Reconnect your Chromecast with the app and stream that video again.
Video streaming should be working alright again.