AVAudioPlayer 不播放文件夹内的歌曲？

我使用此代码来播放歌曲，但它不播放除文档目录之外的文件夹或文件夹中的歌曲。

NSString *songname=[NSString stringWithFormat:@"%@",songArray[songIndex]];
NSLog(@"songname:%@",songname);

NSString* saveFileName = songname;

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *path = [documentsDirectory stringByAppendingPathComponent:saveFileName];
NSURL *url = [[NSURL alloc] initFileURLWithPath: path];
self.audioPlayer=[[AVAudioPlayer alloc] initWithContentsOfURL:url error:NULL];

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *path = [documentsDirectory stringByAppendingPathComponent:@"github.mp4"];
NSURL *url1 = [[NSURL alloc] initFileURLWithPath: path];
avPlayer = [AVPlayer playerWithURL:url1] ;
[self.avplayer play];