如何使用AVAssetWriter保存录制的视频？

Question

我尝试了许多其他博客，并且堆栈溢出。 我没有解决方案，我可以创建带有预览的自定义相机。 我需要带有自定义框架的视频，这就是为什么我使用AVAssetWriter。 但是我无法将录制的视频保存到文档中。 我这样尝试过

-(void) initilizeCameraConfigurations {

if(!captureSession) {

    captureSession = [[AVCaptureSession alloc] init];
    [captureSession beginConfiguration];
    captureSession.sessionPreset = AVCaptureSessionPresetHigh;
    self.view.backgroundColor = UIColor.blackColor;
    CGRect bounds = self.view.bounds;
    captureVideoPreviewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:captureSession];
    captureVideoPreviewLayer.backgroundColor = [UIColor clearColor].CGColor;
    captureVideoPreviewLayer.bounds = self.view.frame;
    captureVideoPreviewLayer.connection.videoOrientation = AVCaptureVideoOrientationPortrait;
    captureVideoPreviewLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;
    captureVideoPreviewLayer.position = CGPointMake(CGRectGetMidX(bounds), CGRectGetMidY(bounds));
    [self.view.layer addSublayer:captureVideoPreviewLayer];
    [self.view bringSubviewToFront:self.controlsBgView];
}


// Add input to session
NSError *err;
videoCaptureDeviceInput  = [AVCaptureDeviceInput deviceInputWithDevice:videoCaptureDevice error:&err];

if([captureSession canAddInput:videoCaptureDeviceInput]) {
    [captureSession addInput:videoCaptureDeviceInput];
}

docPathUrl = [[NSURL alloc] initFileURLWithPath:[self getDocumentsUrl]];

assetWriter = [AVAssetWriter assetWriterWithURL:docPathUrl fileType:AVFileTypeQuickTimeMovie error:&err];
NSParameterAssert(assetWriter);
//assetWriter.movieFragmentInterval = CMTimeMakeWithSeconds(1.0, 1000);

NSDictionary *videoSettings = [NSDictionary dictionaryWithObjectsAndKeys:
                               AVVideoCodecH264, AVVideoCodecKey,
                               [NSNumber numberWithInt:300], AVVideoWidthKey,
                               [NSNumber numberWithInt:300], AVVideoHeightKey,
                               nil];




 writerInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo outputSettings:videoSettings];
 writerInput.expectsMediaDataInRealTime = YES;
 writerInput.transform = CGAffineTransformMakeRotation(M_PI);

 NSDictionary *sourcePixelBufferAttributesDictionary = [NSDictionary dictionaryWithObjectsAndKeys: [NSNumber numberWithInt:kCVPixelFormatType_32BGRA], kCVPixelBufferPixelFormatTypeKey,
 [NSNumber numberWithInt:300], kCVPixelBufferWidthKey,
 [NSNumber numberWithInt:300], kCVPixelBufferHeightKey,
 nil];

 assetWriterPixelBufferInput = [AVAssetWriterInputPixelBufferAdaptor assetWriterInputPixelBufferAdaptorWithAssetWriterInput:writerInput sourcePixelBufferAttributes:sourcePixelBufferAttributesDictionary];


 if([assetWriter canAddInput:writerInput]) {
 [assetWriter addInput:writerInput];
 }

     // Set video stabilization mode to preview layer
AVCaptureVideoStabilizationMode stablilizationMode = AVCaptureVideoStabilizationModeCinematic;
if([videoCaptureDevice.activeFormat isVideoStabilizationModeSupported:stablilizationMode]) {
    [captureVideoPreviewLayer.connection setPreferredVideoStabilizationMode:stablilizationMode];
}


// image output
stillImageOutput = [[AVCaptureStillImageOutput alloc] init];
NSDictionary *outputSettings = [[NSDictionary alloc] initWithObjectsAndKeys: AVVideoCodecJPEG, AVVideoCodecKey, nil];
[stillImageOutput setOutputSettings:outputSettings];
[captureSession addOutput:stillImageOutput];

[captureSession commitConfiguration];
if (![captureVideoPreviewLayer.connection isEnabled]) {
    [captureVideoPreviewLayer.connection setEnabled:YES];
}
[captureSession startRunning];

}
-(IBAction)startStopVideoRecording:(id)sender {

if(captureSession) {
    if(isVideoRecording) {
        [writerInput markAsFinished];

        [assetWriter finishWritingWithCompletionHandler:^{
            NSLog(@"Finished writing...checking completion status...");
            if (assetWriter.status != AVAssetWriterStatusFailed && assetWriter.status == AVAssetWriterStatusCompleted)
            {
                // Video saved
            } else
            {
                NSLog(@"#123 Video writing failed: %@", assetWriter.error);
            }

        }];

    } else {

        [assetWriter startWriting];
        [assetWriter startSessionAtSourceTime:kCMTimeZero];
        isVideoRecording = YES;

    }
}
}
-(NSString *) getDocumentsUrl {

NSString *docPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
docPath = [[docPath stringByAppendingPathComponent:@"Movie"] stringByAppendingString:@".mov"];
if([[NSFileManager defaultManager] fileExistsAtPath:docPath]) {
    NSError *err;
    [[NSFileManager defaultManager] removeItemAtPath:docPath error:&err];
}
NSLog(@"Movie path : %@",docPath);
return docPath;


}


@end

如果有什么问题请指正。 先感谢您。

Answer 1

您没有说出实际出了什么问题，但是您的代码有两点看起来不对：

docPath = [[docPath stringByAppendingPathComponent:@"Movie"] stringByAppendingString:@".mov"];

看起来像它会在以下位置创建类似@"/path/Movie/.mov"的不需要的路径：

docPath = [docPath stringByAppendingPathComponent:@"Movie.mov"];

而且您的时间安排有误。 您的资产写作者从时间0开始，但是sampleBuffer的开始是CMSampleBufferGetPresentationTimestamp(sampleBuffer) > 0 ，所以可以这样做：

-(void)captureOutput:(AVCaptureOutput *)output didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection {
    if(firstSampleBuffer) {
        [assetWriter startSessionAtSourceTime:CMSampleBufferGetPresentationTimestamp(sampleBuffer)];
    }

    [writerInput appendSampleBuffer:sampleBuffer];

}

Answer 2

从概念上讲，您必须涉及主要的功能区域：一个生成视频帧（此为AVCaptureSession ，并附加所有内容），另一个生成视频帧至文件（在您的情况下为AVAssetWriter带有附加输入）。
您的代码存在的问题是：两者之间没有任何联系。 从捕获会话中出来的视频帧/图像不会传递到资产编写器输入。

此外，没有调用AVCaptureStillImageOutput方法-captureStillImageAsynchronouslyFromConnection:completionHandler: AVCaptureStillImageOutput因此捕获会话实际上不生成任何帧。

因此，至少要实现以下内容：

-(IBAction)captureStillImageAndAppend:(id)sender
{
    [stillImageOutput captureStillImageAsynchronouslyFromConnection:stillImageOutput.connections.firstObject completionHandler:
        ^(CMSampleBufferRef imageDataSampleBuffer, NSError* error)
        {
            // check error, omitted here
            if (CMTIME_IS_INVALID( startTime)) // startTime is an ivar
                [assetWriter startSessionAtSourceTime:(startTime = CMSampleBufferGetPresentationTimeStamp( imageDataSampleBuffer))];
            [writerInput appendSampleBuffer:imageDataSampleBuffer];
        }];
}

删除未使用的AVAssetWriterInputPixelBufferAdaptor 。

但是AVCaptureStillImageOutput存在问题：

• 它仅用于产生静止图像，而不是视频

• 如果资产编写器输入配置为压缩附加的样本缓冲区，则必须将其配置为产生未压缩的样本缓冲区（ stillImageOutput.outputSettings = @{ (NSString*)kCVPixelBufferPixelFormatTypeKey: @(kCVPixelFormatType_420YpCbCr8BiPlanarFullRange)}; ）

• 在iOS下已弃用

如果你真的想制作一个视频，而不是静止图像的序列，而不是AVCaptureStillImageOutput添加AVCaptureVideoDataOutput到捕获会话。 它需要一个委托和一个串行调度队列来输出样本缓冲区。 委托必须实现这样的事情：

-(void)captureOutput:(AVCaptureOutput*)output didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection*)connection
{
    if (CMTIME_IS_INVALID( startTime)) // startTime is an ivar
        [assetWriter startSessionAtSourceTime:(startTime = CMSampleBufferGetPresentationTimeStamp( sampleBuffer))];
    [writerInput appendSampleBuffer:sampleBuffer];
}

注意

• 您将要确保AVCaptureVideoDataOutput仅在实际录制时才输出帧； 从捕获会话中添加/删除它，或在startStopVideoRecording操作中启用/禁用其连接

• 在开始另一个记录之前，将startTime重置为kCMTimeInvalid