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Apologize for the late response. To make it easier to talk and listen to the Google Assistant while casting content, the Assistant can automatically lower the volume of videos and music being casted to TVs. This feature is on by default, but there's a way to prevent Assistant from lowering volume.
Follow these steps below to know-how:
Hope this helps.
I have the same problem. It used to work fine but now it seems to be broken.
@Muddi The problem is the Google speaker lowest vizio TV volume but no longer raises volume after it is done. So tv essentially just ends up stuck muted. My tv is up to date using cast version 1.50.243780
Hopefully there will be a bug fix soon?
I hate to bump my own post, but it's been over 2 months since this bug was first reported and it still hasn't been fixed. Is there a better way to submit a bug report? It's a bit tricky because the problem may be the google speaker or the chromecast software, or vizio's implementation of it.
I am truly sorry for the trouble and frustration that you are having with the device, and for the delayed reply. I understand that is not the most ideal situation, and I am more than happy to assist. Since you have exhausted all troubleshooting steps, I would like to escalate this to a higher team.
If you could please fill out this form, our Team would then be in contact with you for additional support. Please let me know if you have any questions from here as well.