To fix this issue, please try the steps below;

1. Turn on "Absolute Volume" in the developer options or select "Sync Bluetooth device volume with phone" in the Bluetooth settings.

2. Make sure the charging case has enough power and reset the earbuds as per the steps below:

- Place the earbuds in the charging case and leave the case open. 

- Press and hold the charging case button for 10 seconds until the LED strip flashes white rapidly three times. This confirms that the reset is successful. 

3. Re-pair your earbuds and turn up the volume of both your phone and earbuds with the music/video to the maximum. 

4. Use a Q-tip with a bit of rubbing alcohol to gently clean the metal mesh filter under the rubber ear tips.