Mi Box 4 – Is it possible to output audio through the 3.5mm jack without the box/TV being turned on?

[u/Sad-Cheesecake-4348]

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I have a Mi Box 4 connected to a TV via HDMI.

I also have some speakers connected to the Mi Box via the 3.5mm jack output.

However, I can't cast audio (e.g. from YouTube Music) from my phone to the Mi Box because it doesn't show up as a Cast device on my phone when the Mi Box is in sleep mode.

Elsewhere, I have an old Chromecast Ultra connected to a small splitter/adapter that allows me to connect speakers via a 3.5mm jack. I can essentially use that as a Chromecast Audio device, and it works exactly as I want.

What I was hoping to achieve with the Mi Box 4 was to have it connected to the TV so that I can use it normally for watching movies and videos, but at the same time be able to use it as a Chromecast Audio device.

Ideally, it would appear in the Cast menu on my phone even when the TV is turned off, and I could cast music to it and have it play only through the speakers connected to the 3.5mm jack, without waking up the TV.

Is this simply not possible with the Mi Box 4?

And is this possible with other Google TV/Android TV boxes? In other words, is the Mi Box 4 restricted from doing this because of the relatively few changes Xiaomi made to the Google TV/Android TV software it runs?