Using a Xiaomi mi box 3s with the latest public update.
Yesterday I had a strange problem watching a movie I bought on Google's Play Store. Until then I never bought a movie on that store. Watching the trailer never gave me any problems: definition was good and audio too.
Thing is when the movie (Fantastic Beasts and where to find them...) starts after a couple seconds I realize that the audio is not working. So I start messing with the box, doing my usual things I do when I'm encountering a problem: reboot, check if it's installing something (updating an app or updating the system in the background), then I try changing the sound modes on the device looking if the movie has some problem with one of them (normally on LINE by default), and finally I try hard rebooting it.
So now I think that the problem might be with my audio setup. I have the box connected with an optical cable to an old but powerful stereo sound system that it everyday use is off (we use it to listen to Spotify ...). So thinking that the app might be detecting it i remove the cable from the box and reboot the device: still not working. I connect the optical cable and, why not, I try turning on the stereo system and magically sound starts coming out !!!
The problem is that from the television is coming sound but from the stereo system a loud beep. I try switching the sound mode on the box hoping for it to solve it but LINE mode is the only mode in which I have sound coming from the TV or Stereo. So finally I have a "great idea" (note that turning off the stereo sound system makes the movie magically not output sound from the TV): turn down the volume of the stereo to 0 (the beep goes away) and just watch it like this.
The movie starts normal music etcetera but at the first scene, I notice that I'm hearing just the background music and the soundtrack, but the primary channel in which the characters are talking is muted so finally I give up. I get the phone and try just one thing: casting it from the phone, and it works, no clue why but it does.
Looking for help if someone knows why ??
UPDATE 12/13/2018
Today I see that there is an update on the Play Store for the movies app, and since now I never tried again to play the movie that gave me problems, so now I launch and after multiple updates to the box itself and to the apps it works.
Xiaomi launched an update to the Mibox for Android Oreo at the beginning of July 2018 and since then, several issues including no 5.1 sound have been registered and basically ignored - with no official response.
They had opened a Beta with Xiaomi.eu but because of some stupid internal dispute, are no longer giving feedback from there and the Mibox forum was deleted.
There is a facebook group for feedback on this, but the bug list they have is totally incomplete and will amount to nothing: https://www.facebook.com/groups/mibox/
The bug list is still available on this post from XDA: https://www.xda-developers.com/xiaomi-mi-box-android-oreo-beta-re-opened/
My advice? sell the Mibox and buy the Nvidia Shield and don't buy anything from Xiaomi again (I have the Yeelights 5 of them and due to software issues also, they are since last weekend working like crap also).
You give peanuts, you get monkeys ... that's the lesson here.