在iOS中使用AVAudioPlayer和MPMusicPlayerController在歌曲播放列表中添加渐变效果

Question

I need to add fade in/out feature in songs playlist (playlist songs are retrive from ipod library). When one song end i need to fade out effect and next song start i need to fade in effect and one other think during fading system or media VOLUME should not changed.

I am using MPMusicPlayerController for play song.

Answer 1

Here is an extension to AVAudioPlayer that I wrote (pre-ARC) that does exactly what you want.

The header AVAudioPlayer+FadeControl.h :

#import <Foundation/Foundation.h>
#import <AVFoundation/AVFoundation.h>


@interface AVAudioPlayer (FadeControl)

-(void)fadeOutWithDuration:(NSTimeInterval)inFadeOutTime;

@end

And the source AVAudioPlayer+FadeControl.m :

#import "AVAudioPlayer+FadeControl.h"

#define     kFadeSteps  20.0

@implementation AVAudioPlayer (FadeControl)

-(void)fadeOutWithDuration:(NSTimeInterval)inFadeOutTime
{
    NSTimeInterval fireInterval = inFadeOutTime/kFadeSteps;
    float volumeDecrement = 1.0/kFadeSteps;
    float originalVolume = self.volume;

    self.volume = originalVolume - volumeDecrement;

    [self retain];
    [NSTimer scheduledTimerWithTimeInterval:fireInterval target:self selector:@selector(fadeOutTimerMethod:) userInfo:[NSNumber numberWithFloat:originalVolume] repeats:YES];

}

- (void)fadeOutTimerMethod:(NSTimer*)theTimer   
{
    float volumeDecrement = 1.0/kFadeSteps;

    if (self.volume > volumeDecrement)
    {
        self.volume = self.volume - volumeDecrement;
    }
    else if ( [theTimer isValid] )
    {
        [self stop];

        NSNumber* originalVolume = [theTimer userInfo];
        self.volume = [originalVolume floatValue];

        [theTimer invalidate];
    }
    else 
    {
        [self stop];
        [self release];
    }


}

@end

It should be trivial to ad an playWithFadeInDuration: method. To use in an ARC project, just add -fno-objc-arc to the file's compile flags.

Answer 2

-(void)doFadeInVolume { 

//play
[audioPlayerMain play];

if (audioPlayerMain.volume < 1.0) {
audioPlayerMain.volume = audioPlayerMain.volume + 0.1;
[self performSelector:@selector(doVolumeFadeMainIn) withObject:nil afterDelay:0.2];
} 
}

And can use the opposite approach for fading out the volume. Hope this helps.