Thanks for reaching out. Please note that we don't officially support pairing Nest any of our Google Home and Nest speakers with Chromecast or cast-enabled TV as an audio output for video playing. Our Google Home/Nest devices are standalone speaker/displays, and it is best to add it on your TV with a Chromecast device in a speaker group to play music, podcasts, and other audio entertainment.
We're always looking for ways to improve -- we'll take this as feedback, and we'll gladly pass it along to the team. You can also send feedback using your device by saying, "Hey Google, send feedback." Visit this link for more steps.