概述

AVFoundation 是一個(gè)可以用來(lái)使用和創(chuàng)建基于時(shí)間的視聽(tīng)媒體數(shù)據(jù)的框架瑞眼。AVFoundation 的構(gòu)建考慮到了目前的硬件環(huán)境和應(yīng)用程序，其設(shè)計(jì)過(guò)程高度依賴多線程機(jī)制。充分利用了多核硬件的優(yōu)勢(shì)并大量使用block和GCD機(jī)制厢漩，將復(fù)雜的計(jì)算機(jī)進(jìn)程放到了后臺(tái)線程運(yùn)行。會(huì)自動(dòng)提供硬件加速操作，確保在大部分設(shè)備上應(yīng)用程序能以最佳性能運(yùn)行疮胖。該框架就是針對(duì)64位處理器設(shè)計(jì)的，可以發(fā)揮64位處理器的所有優(yōu)勢(shì)闷板。

iOS 媒體環(huán)境.png

切換攝像頭

一般來(lái)說(shuō)iPhone都具有前后兩個(gè)攝像頭澎灸，在做相機(jī)應(yīng)用的時(shí)候一個(gè)基本的需求就是前后攝像頭的切換。在切換相機(jī)的時(shí)候我們需要注意的是我們都需要判斷當(dāng)前設(shè)備支不支持相機(jī)切換遮晚、用戶是否開(kāi)啟了相應(yīng)的權(quán)限性昭、以及設(shè)置的圖片尺寸前后攝像頭是否支持這樣的尺寸。

#pragma mark - 切換攝像頭
- (AVCaptureDevice *)deviceWithPostion:(AVCaptureDevicePosition)position
{
    NSArray *devices = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];
    for (AVCaptureDevice *device in devices) {
        if (device.position == position) {
            return device;
        }
    }
    return nil;
}

- (BOOL)canSwitchCamera
{
    return [[AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo] count] > 1;
}

- (void)switchCamera
{
    if (![self canSwitchCamera]) {
        return;
    }
    
    AVCaptureDevicePosition devicePosition;
    if (self.deviceInput.device.position == AVCaptureDevicePositionBack) {
        devicePosition = AVCaptureDevicePositionFront;
    }else {
        devicePosition = AVCaptureDevicePositionBack;
    }
    
    [self.captureSession beginConfiguration];
    [self.captureSession removeInput:_deviceInput];
    NSError *error;
    AVCaptureDevice *device = [self deviceWithPostion:devicePosition];
    self.deviceInput = [AVCaptureDeviceInput deviceInputWithDevice:device error:&error];
    if (!self.deviceInput) {
        [self.captureSession commitConfiguration];
        return;
    }
    [self.captureSession addInput:self.deviceInput];
    [self.captureSession commitConfiguration];
}

調(diào)整焦距

iOS設(shè)備大多都支持基于給定的興趣點(diǎn)設(shè)置對(duì)焦县遣，我們只需要傳入一個(gè)位置糜颠，系統(tǒng)就會(huì)自動(dòng)在當(dāng)前位置進(jìn)行對(duì)焦。 需要注意的是萧求，定要先設(shè)置位置其兴，再設(shè)置曝光模式。需要注意的是夸政，要先設(shè)置位置元旬，再設(shè)置對(duì)焦模式。這里的 CGPoint 取值范圍是取景框左上角（0，0）到取景框右下角（1法绵，1）之間箕速。

#pragma mark - 自動(dòng)對(duì)焦
- (void)autoFocus
{
    if (!self.deviceInput.device) {
        return;
    }
    
    if ([self.deviceInput.device isFocusModeSupported:AVCaptureFocusModeAutoFocus]) {
        NSError *error;
        if ([self.deviceInput.device lockForConfiguration:&error]) {
            self.deviceInput.device.focusMode = AVCaptureFocusModeAutoFocus;
            [self.deviceInput.device unlockForConfiguration];
        }
    }
}

#pragma mark - 調(diào)整焦距
- (BOOL)canTapFoucus
{
    return [self.deviceInput.device isFocusPointOfInterestSupported];
}

- (void)focusAtPoint:(CGPoint)point
{
    if (![self canTapFoucus]) {
        return;
    }
    
    if ([self.deviceInput.device isFocusModeSupported:AVCaptureFocusModeAutoFocus]) {
        NSError *error;
        if ([self.deviceInput.device lockForConfiguration:&error]) {
            self.deviceInput.device.focusPointOfInterest = point;
            self.deviceInput.device.focusMode = AVCaptureFocusModeAutoFocus;
            [self.deviceInput.device unlockForConfiguration];
        }
    }
}

曝光

iOS設(shè)備大多都支持基于給定的興趣點(diǎn)設(shè)置曝光數(shù)據(jù)，我們只需要傳入一個(gè)位置朋譬，系統(tǒng)就會(huì)自動(dòng)在當(dāng)前位置進(jìn)行曝光盐茎。 需要注意的是，定要先設(shè)置位置徙赢，再設(shè)置曝光模式字柠。這里的 CGPoint 取值范圍是取景框左上角（0，0）到取景框右下角（1狡赐，1）之間窑业。

#pragma mark - 曝光
- (BOOL)canTapExpose
{
    return [self.deviceInput.device isExposurePointOfInterestSupported];
}

- (void)exposeAtPoint:(CGPoint)point
{
    if (![self canTapExpose]) {
        return;
    }
    
    if ([self.deviceInput.device isExposureModeSupported:AVCaptureExposureModeAutoExpose]) {
        NSError *error;
        if ([self.deviceInput.device lockForConfiguration:&error]) {
            self.deviceInput.device.exposurePointOfInterest = point;
            self.deviceInput.device.exposureMode = AVCaptureExposureModeAutoExpose;
            [self.deviceInput.device unlockForConfiguration];
        }
    }
}

閃光燈

閃光燈的使用比較簡(jiǎn)單，有以下幾個(gè)模式：AVCaptureFlashModeOff 枕屉、AVCaptureFlashModeOn常柄、AVCaptureFlashModeAuto。

#pragma mark - 閃光燈
- (BOOL)haveFlash
{
    return [self.deviceInput.device hasFlash];
}

- (AVCaptureFlashMode)currentFlashMode
{
    return self.deviceInput.device.flashMode;
}

- (void)setFlashModel:(AVCaptureFlashMode)flashModel
{
    if (self.deviceInput.device.flashMode == flashModel) {
        return;
    }
    
    if ([self.deviceInput.device isFlashModeSupported:flashModel]) {
        NSError *error;
        if ([self.deviceInput.device lockForConfiguration:&error]) {
            self.deviceInput.device.flashMode = flashModel;
            [self.deviceInput.device unlockForConfiguration];
        }
    }
}

手電筒

手電筒的使用比較簡(jiǎn)單搀擂，有以下幾個(gè)模式：AVCaptureTorchModeOff西潘，AVCaptureTorchModeOn，AVCaptureTorchModeAuto 哨颂。

#pragma mark - 手電筒
- (BOOL)haveTorch
{
    return [self.deviceInput.device hasTorch];
}

- (AVCaptureTorchMode)currentTorchMode
{
    return self.deviceInput.device.torchMode;
}

- (void)setTorchModel:(AVCaptureTorchMode)torchModel
{
    if (self.deviceInput.device.torchMode == torchModel) {
        return;
    }
    
    if ([self.deviceInput.device isTorchModeSupported:torchModel]) {
        NSError *error;
        if ([self.deviceInput.device lockForConfiguration:&error]) {
            self.deviceInput.device.torchMode = torchModel;
            [self.deviceInput.device unlockForConfiguration];
        }
    }
}

- (void)setTorchLevel:(float)torchLevel
{
    if ([self.deviceInput.device isTorchActive]) {
        NSError *error;
        if ([self.deviceInput.device lockForConfiguration:&error]) {
            [self.deviceInput.device setTorchModeOnWithLevel:torchLevel error:&error];
            [self.deviceInput.device unlockForConfiguration];
        }
    }
}

保存圖片

使用ALAssetsLibrary喷市，我們可以很方便地將照片或視頻寫入用戶的資源庫(kù)中。在使用的時(shí)候需要注意用戶權(quán)限的控制威恼。

#pragma mark - 保存圖片
- (void)writeImageToPhotosAlbum:(UIImage *)image
{
    ALAssetsLibrary *assetsLib = [[ALAssetsLibrary alloc] init];
    [assetsLib writeImageToSavedPhotosAlbum:image.CGImage
                                orientation:(NSInteger)image.imageOrientation
                            completionBlock:^(NSURL *assetURL, NSError *error) {
        NSLog(@"%@", assetURL);
    }];
}

視頻縮放

縮放的屬性是videoMaxZoomFactor品姓，它的最小值是1.0(不進(jìn)行縮放)，最大值由videoMaxZoomFactor確定箫措。

#pragma mark - 視頻縮放
- (BOOL)videoCanZoom
{
    return self.deviceInput.device.activeFormat.videoMaxZoomFactor > 1.0f;
}

- (float)videoMaxZoomFactor
{
    return MIN(self.deviceInput.device.activeFormat.videoMaxZoomFactor, 4.0f);
}

- (void)setVideoZoomFactor:(float)factor
{
    if (self.deviceInput.device.isRampingVideoZoom) {
        return;
    }
    
    NSError *error;
    if ([self.deviceInput.device lockForConfiguration:&error]) {
        self.deviceInput.device.videoZoomFactor = pow([self videoMaxZoomFactor], factor);
        [self.deviceInput.device unlockForConfiguration];
    }
}

- (void)rampZoomToFactor:(float)factor
{
    if (self.deviceInput.device.isRampingVideoZoom) {
        return;
    }

    NSError *error;
    if ([self.deviceInput.device lockForConfiguration:&error]) {
        [self.deviceInput.device rampToVideoZoomFactor:pow([self videoMaxZoomFactor], factor) withRate:1.0f];
        [self.deviceInput.device unlockForConfiguration];
    }
}

CoreVideo渲染

為什么要用快速紋理上傳腹备，相比OpenGLES快速紋理上傳大大加快了紋理上傳的速度。這也是GPUImage中為什么優(yōu)先使用快速紋理上傳的原因斤蔓。在閱讀GPUImage源碼的時(shí)候你可以看到這樣的注釋：// Note: the fast texture caches speed up 640x480 frame reads from 9.6 ms to 3.1 ms on iPhone 4S
詳見(jiàn)框架中的 GPUImageRawDataOutput.m 文件

- (void)setupOpenGLTextureCache
{
    CVReturn statuts = CVOpenGLESTextureCacheCreate(kCFAllocatorDefault,
                                                    NULL,
                                                    _context,
                                                    NULL,
                                                    &_openGLESTextureCache);
    if (statuts != kCVReturnSuccess) {
        exit(0);
    }
}

#pragma mark - GLTexture
- (void)genTetureFromImage:(CVImageBufferRef)imageRef
{
    CVOpenGLESTextureCacheCreateTextureFromImage(kCFAllocatorDefault,
                                                _openGLESTextureCache,
                                                imageRef,
                                                NULL,
                                                GL_TEXTURE_2D,
                                                GL_RGBA,
                                                (GLsizei)CVPixelBufferGetWidth(imageRef),
                                                (GLsizei)CVPixelBufferGetHeight(imageRef),
                                                GL_BGRA,
                                                GL_UNSIGNED_BYTE,
                                                0,
                                                &_openGLESTexture);

    glBindTexture(GL_TEXTURE_2D, CVOpenGLESTextureGetName(_openGLESTexture));
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glUniform1i(glGetUniformLocation(_program, "image"), 0);

    if (_openGLESTexture) {
        CFRelease(_openGLESTexture);
        _openGLESTexture = NULL;
        CVOpenGLESTextureCacheFlush(_openGLESTextureCache, 0);
    }
}

在這里不再介紹如何實(shí)時(shí)渲染相機(jī)視頻馏谨，當(dāng)前在本文的例子中完成了相機(jī)視頻的實(shí)時(shí)渲染，具體請(qǐng)參考之前的文章或本文的相關(guān)示例附迷。

參考

AVFoundation開(kāi)發(fā)秘籍:實(shí)踐掌握iOS & OSX應(yīng)用的視聽(tīng)處理技術(shù)

源碼地址：AVFoundation開(kāi)發(fā) https://github.com/QinminiOS/AVFoundation