The Xiaomi 'MI Box S (Google Assistant)', like many other streaming devices, has limitations when it comes to playing AVI files directly.

- Compatibility: The MI Box S, which runs on Android TV, may not natively support all types of AVI files. AVI is a container format that can contain various codecs, and not all of these codecs are supported by the MI Box S.
- Solution: To play AVI files on your MI Box S, you may need to convert them to a more compatible format such as MP4 or MKV. You can use video conversion software like HandBrake, VLC, or other video converters to achieve this.
- Alternative: If you prefer not to convert files, you can use apps like VLC or other media players that support a wider range of formats, including AVI. However, the compatibility still depends on the specific codecs used within the AVI files.

In summary, while the MI Box S may not support all AVI files out of the box, converting the files or using a compatible media player can help resolve the issue.