avplayer has no sounds when play video

Check if the iPhone has silent mode engaged, it is a button above the 2 top left buttons. A toggle switch that allows silent mode.

For Swift 4.2, put following lines in viewDidLoad

do {
    try AVAudioSession.sharedInstance().setCategory(.playback, mode: .default, options: [])
}
catch {
    print("Setting category to AVAudioSessionCategoryPlayback failed.")
}

For Swift 5

do {
            try AVAudioSession.sharedInstance().setCategory(.playback, mode: .default, options: [])
           }
           catch {
               print("Setting category to AVAudioSessionCategoryPlayback failed.")
           }

Check your phone is silent mode or not. If it is silent try add code below to viewDidLoad:

Swift 2.3

try! AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryPlayback, withOptions: [])

Swift 3

try! AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryPlayback, with: [])

Swift 4.2

try! AVAudioSession.sharedInstance().setCategory(.playback, options: [])

Or just

try! AVAudioSession.sharedInstance().setCategory(.playback)