Can I mute for youtube-ios-player-helper?

I'm using youtube-ios-player-helper to play youtube video in my application. I'd like to be able to mute. Here is what I did:

1. Add setVolume() and mute() function in YTPlayerView

   -(void)setVolume:(int)volume {    if ( volume < 0 )        volume = 0;    else if ( volume > 100 )        volume = 100;    NSString *command = [NSString stringWithFormat:@"player.setVolume(%d);", volume];    [self stringFromEvaluatingJavaScript:command];}-(void)mute {            NSString *command = [NSString stringWithFormat:@"player.mute();"];    [self stringFromEvaluatingJavaScript:command];}

Then I call setVolume:0 or mute functions in my app. But the sound can't be turned off. The volume is still 100.

Did anybody turn off the sound successfully?