主要功能如下：
选择歌曲：
剪切歌曲：
VTMViewController.h
#import <UIKit/UIKit.h>
//基库，一系列的Class(类)来建立和管理iPhone OS应用程序的用户界面接口、应用程序对象、事件控制、绘图模型、窗口、视图和用于控制触摸屏等的接口
#import <AVFoundation/AVFoundation.h> //音频处理
#import <MediaPlayer/MediaPlayer.h> //媒体库
@interface VTMViewController : UIViewController <MPMediaPickerControllerDelegate> {
//媒体选择控制器的委托
MPMediaItem *song; //歌曲 媒体类型
UILabel *songLabel; //歌曲 文本类型
UILabel *artistLabel; //艺术家 文本类型
UILabel *sizeLabel; //大小 文本类型
UIImageView *coverArtView; //转化艺术家 图片类型
UIProgressView *conversionProgress; //进度指示器类型
}
//多线成，retain<>IBOutlet引用计数加2还是1，IB控制关联
@property (nonatomic, retain) IBOutlet UILabel *songLabel; //监控song lable文本
@property (nonatomic, retain) IBOutlet UILabel *artistLabel; //监控artist lable文本
@property (nonatomic, retain) IBOutlet UILabel *sizeLabel; //监控0btyes lable文本
@property (nonatomic, retain) IBOutlet UIImageView *coverArtView; //监控UIImageView块
@property (nonatomic, retain) IBOutlet UIProgressView *conversionProgress;
//监控进度条块
//IBAction->IB控件的相应动作关联
-(IBAction) chooseSongTapped: (id) sender; //选择歌曲 通用对象类型参数
-(IBAction) convertTapped: (id) sender;//改变 通用对象类型参数
- (BOOL)exportAsset:(AVAsset *)avAsset toFilePath:(NSString *)filePath;
//字符串类型
@end
VTMViewController.m
//
// VTMViewController.m
// VTM
//
// Created by jinhu zhang on 11-1-15.
// Copyright 2011 no. All rights reserved.
//
#import "VTMViewController.h"
#import <AudioToolbox/AudioToolbox.h> //音频处理
#define EXPORT_NAME @"exported.caf"
@implementation VTMViewController
//合成器
@synthesize songLabel;
@synthesize artistLabel;
@synthesize sizeLabel;
@synthesize coverArtView;
@synthesize conversionProgress;
#pragma mark init/dealloc
//释放内存
- (void)dealloc {
[super dealloc];
}
#pragma mark vc lifecycle
//视图已完全过渡到屏幕上时调用
-(void) viewDidAppear:(BOOL)animated {
[super viewDidAppear:animated];
}
#pragma mark event handlers
/*
选择歌曲， 监听载入Button按钮
从mediaPlayer.framework里的MPMusicPlayerController类来播放ipod库中自带的音乐
*/
-(IBAction) chooseSongTapped: (id) sender {
MPMediaPickerController *pickerController = [[MPMediaPickerController alloc] //初始化
initWithMediaTypes: MPMediaTypeMusic];
pickerController.prompt = @"Choose song to export";//提示
pickerController.allowsPickingMultipleItems = NO; //是否可以多选
pickerController.delegate = self; //委托给自己
[self presentModalViewController:pickerController animated:YES]; //播放选中的歌曲
[pickerController release]; //引用计数减一
}
/*
剪切歌曲，监听剪切按钮
大概流程
1、获取歌曲路径，初始化音频文件
2、返回音频文件数据，测试是否接收器是否正常
3、设置新的音频路径，
4、开始剪切
*/
-(IBAction) convertTapped: (id) sender {
// set up an AVAssetReader to read from the iPod Library
NSURL *assetURL = [song valueForProperty:MPMediaItemPropertyAssetURL]; //获取歌曲地址
AVURLAsset *songAsset = [AVURLAsset URLAssetWithURL:assetURL options:nil]; //初始化音频媒体文件
NSError *assetError = nil; //错误标识
AVAssetReader *assetReader = [[AVAssetReader assetReaderWithAsset:songAsset
error:&assetError]
retain];//指定媒体文件返回数据，返回失败抛出一个错误
/*
如果有错误，则格式化输出错误后，跳出
*/
if (assetError) {
NSLog (@"error: %@", assetError);
return;
}
AVAssetReaderOutput *assetReaderOutput = [[AVAssetReaderAudioMixOutput
assetReaderAudioMixOutputWithAudioTracks:songAsset.tracks
audioSettings: nil]
retain]; //读取指定文件的音频轨道混音
/*
判断是否能够接收器能够正常接收，如果不能，格式化输出提示，跳出
*/
if (! [assetReader canAddOutput: assetReaderOutput]) {
NSLog (@"can't add reader output... die!");
return;
}
[assetReader addOutput: assetReaderOutput];//输出音乐
NSArray *dirs = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);//获取应用程序私有目录
/*
[[[dirs objectAtIndex:0] stringByAppendingPathComponent:EXPORT_NAME]]; 简洁版
*/
NSString *documentsDirectoryPath = [dirs objectAtIndex:0]; //返回第一个对象
NSString *exportPath = [[documentsDirectoryPath stringByAppendingPathComponent:EXPORT_NAME] retain]; //剪切文件名(如果没有就创建，有就打开)
/*
检查目录是否存在，存在则删除
*/
if ([[NSFileManager defaultManager] fileExistsAtPath:exportPath]) {
[[NSFileManager defaultManager] removeItemAtPath:exportPath error:nil];
}
NSURL *exportURL = [NSURL fileURLWithPath:exportPath];//返回文件路径
AVAssetWriter *assetWriter = [[AVAssetWriter assetWriterWithURL:exportURL
fileType:AVFileTypeCoreAudioFormat
error:&assetError]
retain];//开始录制
/*
如果有错误，则格式化输出错误后，跳出
*/
if (assetError) {
NSLog (@"error: %@", assetError);
return;
}
[self exportAsset:songAsset toFilePath:exportPath];
[exportPath release];//引用计数减一
}
/*
剪切开始工作
大概流程
1、获得视频总时长，处理时间，数组格式返回音频数据
2、创建导出会话
3、设计导出时间范围，淡出时间范围
4、设计新音频配置数据，文件路径，类型等
5、开始剪切
*/
- (BOOL)exportAsset:(AVAsset *)avAsset toFilePath:(NSString *)filePath {
// we need the audio asset to be at least 50 seconds long for this snippet
CMTime assetTime = [avAsset duration];//获取视频总时长,单位秒
Float64 duration = CMTimeGetSeconds(assetTime); //返回float64格式
if (duration < 20.0) return NO; //小于20秒跳出
// get the first audio track
NSArray *tracks = [avAsset tracksWithMediaType:AVMediaTypeAudio]; //返回该音频文件数据的数组
if ([tracks count] == 0) return NO; //如果没有数据，跳出
AVAssetTrack *track = [tracks objectAtIndex:0];//获取第一个对象
// create the export session
// no need for a retain here, the session will be retained by the
// completion handler since it is referenced there
//创建导出会话
AVAssetExportSession *exportSession = [AVAssetExportSession
exportSessionWithAsset:avAsset
presetName:AVAssetExportPresetAppleM4A];
if (nil == exportSession) return NO;//创建失败，则跳出
// create trim time range - 20 seconds starting from 30 seconds into the asset
CMTime startTime = CMTimeMake(30, 1);//CMTimeMake(第几帧， 帧率) 30
CMTime stopTime = CMTimeMake(50, 1);//CMTimeMake(第几帧， 帧率)50
CMTimeRange exportTimeRange = CMTimeRangeFromTimeToTime(startTime, stopTime);//导出时间范围
// create fade in time range - 10 seconds starting at the beginning of trimmed asset
CMTime startFadeInTime = startTime;//30
CMTime endFadeInTime = CMTimeMake(40, 1);//40
CMTimeRange fadeInTimeRange = CMTimeRangeFromTimeToTime(startFadeInTime, //淡入时间范围
endFadeInTime);
// setup audio mix
AVMutableAudioMix *exportAudioMix = [AVMutableAudioMix audioMix];//实例新的可变音频混音
AVMutableAudioMixInputParameters *exportAudioMixInputParameters =
[AVMutableAudioMixInputParameters audioMixInputParametersWithTrack:track]; //给track 返回一个可变的输入参数对象
[exportAudioMixInputParameters setVolumeRampFromStartVolume:0.0 toEndVolume:1.0
timeRange:fadeInTimeRange]; //设置指定时间范围内导出
exportAudioMix.inputParameters = [NSArray
arrayWithObject:exportAudioMixInputParameters]; //返回导出数据转化为数组
// configure export session output with all our parameters 新的配置信息
exportSession.outputURL = [NSURL fileURLWithPath:filePath]; // output path 新文件路径
exportSession.outputFileType = AVFileTypeAppleM4A; // output file type 新文件类型
exportSession.timeRange = exportTimeRange; // trim time range //剪切时间
exportSession.audioMix = exportAudioMix; // fade in audio mix //新的混音音频
// perform the export 开始真正工作
[exportSession exportAsynchronouslyWithCompletionHandler:^{ //block
if (AVAssetExportSessionStatusCompleted == exportSession.status) { //如果信号提示已经完成
NSLog(@"AVAssetExportSessionStatusCompleted"); //格式化输出成功提示
} else if (AVAssetExportSessionStatusFailed == exportSession.status) { //如果信号提示已经完成
// a failure may happen because of an event out of your control
// for example, an interruption like a phone call comming in
// make sure and handle this case appropriately
NSLog(@"AVAssetExportSessionStatusFailed"); //格式化输出失败提示
} else {
NSLog(@"Export Session Status: %d", exportSession.status); //格式化输出信号状态
}
}];
return YES;
}
@end