how do you open a file manager app and play video directly?

Add the below code to inside activity(that you want to open) inside manifest:

        <intent-filter>
            <action android:name="android.intent.action.VIEW"/>
            <category android:name="android.intent.category.DEFAULT"/>
            <data android:mimeType="video/*"/>
            <data android:scheme="content"/>
            <data android:scheme="file"/>
        </intent-filter>

use below code to your activity to get the uri of your file. I have tested the path in exoplayer.

Uri uri = getIntent().getData();