What is the reason that the square dance of the downloaded mp4 is played on the mobile EvD with only image but no sound?

Hello pro, I hope it can help pro.1 you can play the MP4 you downloaded with your cell phone or tablet or computer to see if there is sound.2 if there is no sound then it is the problem of the file.3 if there is sound then you need to check if the audio cable of your EVD is plugged in correctly.4 a bad cable or a bad speaker or poor contact will also have no sound , you can re-plug or change a cable to try.