需求

公司混合开发，uni端拍小视频不是很理想，为达到仿微信效果，原生插件走起

思路

第1步：1个AVCaptureSession, 1块AVCaptureVideoPreviewLayer[考虑兼容替换成AVPreView]

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

第3步：代理中设置output区分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, 加入AVAssetWriter

第5步：CMSampleBufferRef不断过来，AssetWriter不断写入，直到停止

上菜

第一步的初始化就不写了，没事可以翻看本人前面的博客

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(@"取得设备摄入videoInput对象时出错, 错误原因: %@", error);
    return;
}

// 设备添加到会话中
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];
}

// 音频相关
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];
}

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

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

第3步：启动Session，代理里面操作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，需要从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);
        }
    });
}

写在末尾：

1. AVAssetWriterInput设置视频属性时，按照自己的需要设计，其中码率与帧率的设置会影响到拍摄后视频的质量与大小，具体看各自项目的要求

2. 如果视频视角存在问题，可以从三个方向入手调整

   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，比如Rotation M_PI/2 角度