ios开发之AVFoundation总结

1, Using Assets ［自己理解为：数据的来源］ 
这个资源可以来自自己的ipod媒体库或图片也可以时文件 
creating an Asset Object 
NSRUL *url = 后跟一个网址 如电影文件等资源 
AVURLAsset *ansset = [[AVURLSset alloc] initwithURL:url  options:nil]; 
2.获得一个视频的图像 
使用AVASsetImageGenerator类来实现 
用来生成图像序列 
3.Playback 
我们在播放视频时可以使用AVPlayer和AVQueuePlayer播放AVPlayer是AVQueuePlayer的父类 
a先创建一个路径 
b可以使用AVPlayerItem加载路径 
c使用AVPlayer播放文件 
当然我们还可以控制它的播放速度 
使用rate属性它是一个介于0.0－－1.0之间的数 
 
我们也可以播放多个项目 
NSArray *items  = // 设置一个播放的组合 
AVQueuePlayer ＊queueplayer ＝ ［［AVQueuePlayer alloc］initwithItems：items］； 
然后使用AVPlayerItem  
AVPlayerItem ＊anItem ＝ ／／ get  a player item 
使用canInsertItem：afterItem 测试 
4.Media capture 
我们可以配置预设图片的质量和分辨率 
Symbol                                                    Resolution        Comments 
AVCaptureSessionPresetHigh        High                  Highest recording quality. This varies per device. 
AVCaptureSessionPresetMedium      Medium            Suitable for WiFi sharing. The actual values may change. 
AVCaptureSessionPresetLow        Low                        Suitable for 3g sharing. The actual values may change. 
AVCaptureSessionPreset640x480    640x480      VGA 
AVCaptureSessionPreset1280x720    1280x720    720p HD 
AVCaptureSessionPresetPhoto                Photo      Full photo resolution. This is not supported for video output 
判断一个设备是否适用 
AVCaptreSessuion *session = [[AVCaptureSession alloc]init]; 
if([session canSetSessionPreset:AVCaptureSessionPrese 1280x720]){ 
session.sessionPreset = AVCaptureSessionPreset 1280x720; 
}else{ 
// Handle the failure. 
} 
当然在 
［session beginConfigration］, 
［session commitconfiguration］之间配置重新添加你想要适用的设备以及删除以前的设备等操作 
5.当我们不知道设备的一些特性时我们可以使用以下代码查找相应的设备 
NSArray *devices = [AVCaptureDevice devices]; 
fo(AVCaptureDevice *device in device){ 
NSLogO("Device name %@",[devic localizedName]); 
当然还可以判断设备的位置 
if([device hasMediaType:AVMediaTypeVideo]){ 
if([device postion] == AVCaptureDevicePostionBack){ 
nslog(@"Device postion :back"); 
}else{ 
NSLog(@"Device postion :front"); 
} 
} 
} 
下面的demo说明如何找到视频输入设备 
NSArray ＊devices = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo]; 
NsMutableArray *torchDevices =  [[NSMutableArray alloc]init];  
for(AVCaptureDevice *device in devices){ 
if([device hasTorch]&&[device supportsAVCaptureSessionPreset:AVCaptureSessionPreset 640x480]){ 
[torchDevices addObject:device]; 
} 
} 
 
6设备间切换 
AVCaptureSession *session = //一个设备session 
[session beginConfiguration]; 
 
[session removeInput:frontFacingCameraDeviceInput]; 
[session AddInput:backFacikngCameraDeviceInput]; 
 
[session commitConfiguration]; 
 
7 配置AVCaptureDeviceInput  
AVCaptureSession *captureSession = <#Get a capture session#>;  
AVCaptureDeviceInput *captureDeviceInput = <#Get a capture device input#>;  
// 检查是否适用 
if ([captureSession canAddInput:captureDeviceInput]) { 
// 适用则添加 
[captureSession addInput:captureDeviceInput]; 
} else { 
// Handle the failure. 
} 
8 配置AVCaptureOutput 
输出的类型： 
  a.AVCaptureMovieFileOutput 输出一个电影文件 
b.AVCaptureVideoDataOutput 输出处理视频帧被捕获 
c.AVCaptureAudioDataOutput 输出音频数据被捕获 
d.AVCaptureStillImageOutput 捕获元数据 
AVCaptureSession *captureSession = <#Get a capture session#>; 
AVCaptureMovieFileOutput *movieInput = <#Create and configure a movie output#>;  
if ([captureSession canAddOutput:movieInput]) { 
[captureSession addOutput:movieInput]; 
} else { 
// Handle the failure. 
} 
9 保存到一个电影文件 
AVCaptureMovieFileOutput *aMovieFileOutput = [[AVCaptureMovieFileOutput alloc] init]; 
CMTime maxDuration = <#Create a CMTime to represent the maximum duration#>; aMovieFileOutput.maxRecordedDuration = maxDuration;  
aMovieFileOutput.minFreeDiskSpaceLimit = <#An appropriate minimum given the quality of the movie format and the duration#>; 
10 录音设备 
The delegate must conform to the  
AVCaptureFileOutputRecordingDelegate  
protocol,  
and must implement the  
captureOutput:didFinishRecordingToOutputFileAtURL:fromConnections:error: method. 
11 像素和编码格式 
iphone 3G      iphone 3GS                      iphone 4 
yuvs,2vuy,BGRA,jpeg    420f,420v,BGRA,jpeg        420f, 420v, BGRA, jpeg 
12  静态图像捕捉 
AVCaptureStillImageOutput *stillImageOutput = [[AVCaptureStillImageOutput alloc] init]; 
NSDictionary *outputSettings = [[NSDictionary alloc] initWithObjectsAndKeys:AVVideoCodecJPEG,AVVideoCodecKey, nil]; [stillImageOutput setOutputSettings:outputSettings]; 
13 重力模式 
The preview layer supports three gravity modes that you set using videoGravity: 
● AVLayerVideoGravityResizeAspect: This preserves the aspect ratio, leaving black bars where the 
video does not fill the available screen area. 
● AVLayerVideoGravityResizeAspectFill: This preserves the aspect ratio, but fills the available screen area, cropping the video when necessary. 
● AVLayerVideoGravityResize: This simply stretches the video to fill the available screen area, even if doing so distorts the image. 
 
 
设备之间切换 
- (AVCaptureDevice *)cameraWithPosition:(AVCaptureDevicePosition)position 
{ 
    NSArray *devices = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo]; 
    for ( AVCaptureDevice *device in devices ) 
        if ( device.position == position ) 
            return device; 
    return nil; 
} 
 
- (void)swapFrontAndBackCameras { 
    // Assume the session is already running 
 
    NSArray *inputs = self.session.inputs; 
    for ( AVCaptureDeviceInput *input in inputs ) { 
        AVCaptureDevice *device = input.device; 
        if ( [device hasMediaType:AVMediaTypeVideo] ) { 
            AVCaptureDevicePosition position = device.position; 
            AVCaptureDevice *newCamera = nil; 
            AVCaptureDeviceInput *newInput = nil; 
 
            if (position == AVCaptureDevicePositionFront) 
                newCamera = [self cameraWithPosition:AVCaptureDevicePositionBack]; 
            else 
                newCamera = [self cameraWithPosition:AVCaptureDevicePositionFront]; 
            newInput = [AVCaptureDeviceInput deviceInputWithDevice:newCamera error:nil]; 
 
            // beginConfiguration ensures that pending changes are not applied immediately 
            [self.session beginConfiguration]; 
 
            [self.session removeInput:input]; 
            [self.session addInput:newInput]; 
 
            // Changes take effect once the outermost commitConfiguration is invoked. 
            [self.session commitConfiguration]; 
            break; 
        } 
    }  
}