Can I control slider value programmatically?

I have used following code

    for (UIView *view in [volumeView subviews]){
        if ([[[view class] description] isEqualToString:@"MPVolumeSlider"]) {
            volumeViewSlider = (UISlider *) view;
        }
    }

    //[volumeViewSlider setBackgroundColor:[UIColor colorWithRed:1.00 green:0.0 blue:0.0 alpha:1.0]];
    UIImage *stetchLeftTrack = [[UIImage imageNamed:@"leftslide.png"]
                                stretchableImageWithLeftCapWidth:10.0 topCapHeight:0.0];
    UIImage *stetchRightTrack = [[UIImage imageNamed:@"rightslide.png"]
                                 stretchableImageWithLeftCapWidth:10.0 topCapHeight:0.0];
    //    [customSlider setThumbImage: [UIImage imageNamed:@"slider_ball.png"] forState:UIControlStateNormal];
    [volumeViewSlider setMinimumTrackImage:stetchLeftTrack forState:UIControlStateNormal];
    [volumeViewSlider setMaximumTrackImage:stetchRightTrack forState:UIControlStateNormal];
    [volumeViewSlider setMinimumValueImage:[UIImage imageNamed:@"SpeakerSoft.tif"]];
    [volumeViewSlider setMaximumValueImage:[UIImage imageNamed:@"SpeakerLoud.tif"]];


    [NSTimer scheduledTimerWithTimeInterval:60.0 target:self selector:@selector(changeTheTimer) userInfo:nil repeats:NO];
}

-(void)changeTheTimer{
    [volumeViewSlider setValue:0 animated:YES];
    NSLog(@"Value is set to 0");
}

I want to stop all playbacks after one minute , but slider moves to zero and leaves of effect of master volume.

You can certainly make use of the UISlider instance method

- (void)setValue:(float)value animated:(BOOL)animated

This will reduce the slider value with or without animation.

UPDATE

Check this link on Controlling Master Volume