关于ios:iOS拍个小视频

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需要
公司混合开发，uni 端拍小视频不是很现实，为达到仿微信成果，原生插件走起
思路
第 1 步：1 个 AVCaptureSession, 1 块 AVCaptureVideoPreviewLayer[思考兼容替换成 AVPreView]

第 2 步：视频录制需 video & audio, 须要对应的 AVCaptureDeviceInput，同理对应的 AVCaptureVideoDataOutput 与 AVCaptureAudioDataOutput

第 3 步：代理中设置 output 辨别 video 与 audio, 并将对应的 CMSampleBufferRef 写入到视频文件中

第 4 步：写入视频文件中，用到 AVAssetWriter, 对应 video & audio 需两个 AVAssetWriterInput, 退出 AVAssetWriter

第 5 步：CMSampleBufferRef 一直过去，AssetWriter 一直写入，直到进行

上菜

第一步的初始化就不写了，没事能够翻看自己后面的博客

第 2 步：两个 AVCaptureDeviceInput 两个 Output, 且设置 Output 的代理

self.videoInput = [[AVCaptureDeviceInput alloc] initWithDevice:device error:&error];
if (error) {NSLog(@"获得设施摄入 videoInput 对象时出错, 谬误起因: %@", error);
    return;
}

// 设施增加到会话中
if ([self.session canAddInput:self.videoInput]) {[self.session addInput:self.videoInput];
}

[self.videoOutput setSampleBufferDelegate:self queue:self.videoQueue];
if ([self.session canAddOutput:self.videoOutput]) {[self.session addOutput:self.videoOutput];
}

// 音频相干
AVCaptureDevice *adevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeAudio];
self.audioInput = [[AVCaptureDeviceInput alloc] initWithDevice:adevice error:&error];

if ([self.session canAddInput:self.audioInput]) {[self.session addInput:self.audioInput];
}

[self.audioOutput setSampleBufferDelegate:self queue:self.videoQueue];
if ([self.session canAddOutput:self.audioOutput]) {[self.session addOutput:self.audioOutput];
}

// 视频输入
- (AVCaptureVideoDataOutput *)videoOutput {if (!_videoOutput) {_videoOutput = [[AVCaptureVideoDataOutput alloc] init];
        _videoOutput.alwaysDiscardsLateVideoFrames = YES;
    }
    return _videoOutput;
}

// 音频输入
- (AVCaptureAudioDataOutput *)audioOutput {if (!_audioOutput) {_audioOutput = [[AVCaptureAudioDataOutput alloc] init];
    }
    return _audioOutput;
}

第 3 步：启动 Session，代理外面操作 CMSampleBufferRef

#pragma mark - AVCaptureVideoDataOutputSampleBufferDelegate & AVCaptureAudioDataOutputSampleBufferDelegate
- (void)captureOutput:(AVCaptureOutput *)output didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection {
    @autoreleasepool {
        // 视频
        if (connection == [self.videoOutput connectionWithMediaType:AVMediaTypeVideo]) {if (!self.manager.outputVideoFormatDescription) {@synchronized(self) {CMFormatDescriptionRef formatDescription = CMSampleBufferGetFormatDescription(sampleBuffer);
                    self.manager.outputVideoFormatDescription = formatDescription;
                }
            } else {@synchronized(self) {if (self.manager.state == StateRecording) {[self.manager appendBuffer:sampleBuffer type:AVMediaTypeVideo];
                    }
                }
            }
        }
        
        // 音频
        if (connection == [self.audioOutput connectionWithMediaType:AVMediaTypeAudio]) {if (!self.manager.outputAudioFormatDescription) {@synchronized(self) {CMFormatDescriptionRef formatDescription = CMSampleBufferGetFormatDescription(sampleBuffer);
                    self.manager.outputAudioFormatDescription = formatDescription;
                }
            }
            @synchronized(self) {if (self.manager.state == StateRecording) {[self.manager appendBuffer:sampleBuffer type:AVMediaTypeAudio];
                }
            }
        }
    }
}

第 4 步：AVAssetWriter 以及对应的 Input

// writer 初始化
self.writer = [AVAssetWriter assetWriterWithURL:_videoUrl fileType:AVFileTypeMPEG4 error:nil];

_videoInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo outputSettings:_videoSettings];
//expectsMediaDataInRealTime 必须设为 yes，须要从 capture session 实时获取数据
_videoInput.expectsMediaDataInRealTime = YES;

_audioInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeAudio outputSettings:_audioSettings];
_audioInput.expectsMediaDataInRealTime = YES;

if ([_writer canAddInput:_videoInput]) {[_writer addInput:_videoInput];
}
if ([_writer canAddInput:_audioInput]) {[_writer addInput:_audioInput];
}

第 5 步：第 3 步的 CMSampleBufferRef 通过 AVAssetWriter 写入到视频文件中

- (void)appendBuffer:(CMSampleBufferRef)buffer type:(NSString *)mediaType {if (buffer == NULL) {NSLog(@"empty sampleBuffer");
        return;
    }
    
    @synchronized (self) {if (self.state < StateRecording) {NSLog(@"not ready yet");
            return;
        }
    }
    
    CFRetain(buffer);
    dispatch_async(self.queue, ^{
        @autoreleasepool {@synchronized (self) {if (self.state > StateFinish) {CFRelease(buffer);
                    return;
                }
            }
            
            if (!self.canWrite && mediaType == AVMediaTypeVideo) {[self.writer startWriting];
                [self.writer startSessionAtSourceTime:CMSampleBufferGetPresentationTimeStamp(buffer)];
                self.canWrite = YES;
            }
            
            if(!self.timer) {dispatch_async(dispatch_get_main_queue(), ^{self.timer = [NSTimer scheduledTimerWithTimeInterval:TIMER_INTERVAL target:self selector:@selector(updateProgress) userInfo:nil repeats:YES];
                    [[NSRunLoop currentRunLoop] addTimer:self.timer forMode:NSDefaultRunLoopMode];
                });
            }
            
            // 写入视频数据
            if (mediaType == AVMediaTypeVideo) {if (self.videoInput.readyForMoreMediaData) {BOOL success = [self.videoInput appendSampleBuffer:buffer];
                    if (!success) {@synchronized (self) {[self stop:^{}];
                            [self destroy];
                        }
                    }
                }
            }
            
            // 写入音频数据
            if (mediaType == AVMediaTypeAudio) {if (self.audioInput.readyForMoreMediaData) {BOOL success = [self.audioInput appendSampleBuffer:buffer];
                    if (!success) {@synchronized (self) {[self stop:^{}];
                            [self destroy];
                        }
                    }
                }
            }
            CFRelease(buffer);
        }
    });
}

写在开端：
1. AVAssetWriterInput 设置视频属性时，依照本人的须要设计，其中码率与帧率的设置会影响到拍摄后视频的品质与大小，具体看各自我的项目的要求
2. 如果视频视角存在问题，能够从三个方向动手调整
  1.layer 的 connect 设置下 videoOrientation
  
  2.AVCaptureOutput 的 connect 设置下 videoOrientation
  
  3.AVAssetWriterInput 针对 video 是设置下 transform，比方 Rotation M_PI/2 角度