AVCaptureSession with multiple Outputs?

问题

I'm currently developing an iOS app that applies CoreImage to the camera feed in order to take photos and videos, and I've run into a bit of snag.

Up till now I've been using AVCaptureVideoDataOutput to obtain the sample buffers and manipulate them with CoreImage, and then displayed a simple preview, as well as using it to capture photos and saving them.

When I tried to implement Video Recording, by writing the SampleBuffers to a video as I received them from the AVCaptureVideoDataOutput, it had a very slow frame rate (probably because of the other image relating processing that was going on).

So I was wondering, is it possible to have an AVCaptureVideoDataOutput and a AVCaptureMoveFileOutput going on the same AVCaptureSession simultaneously?

I gave it a quick go, and found that when I added the extra output, my AVCaptureVideoDataOutput stopped receiving information.

If I can get it working, I'm hoping it means that I can simply use the 2nd output to record video at high frame rates, and do post-processing on the video after the user has stopped recording.

Any help will be greatly appreciated.

回答1:

It's easier than you'd think.

See: AVCamDemo

Capture data using AVCaptureVideoDataOutput.
Create a new dispatch queue before recording, eg. recordingQueue: recordingQueue = dispatch_queue_create("Movie Recording Queue", DISPATCH_QUEUE_SERIAL);

In the captureOutput:didOutputSampleBuffer:fromConnection: delegate method, capture the samplebuffer, retain it, and in the recording queue, write it to the file:

-(void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection {    

    CFRetain(sampleBuffer);

    dispatch_async(recordingQueue, ^{

        if (assetWriter) {

            if (connection == videoConnection) {
                [self writeSampleBuffer:sampleBuffer ofType:AVMediaTypeVideo];
            } else if (connection == audioConnection) {
                [self writeSampleBuffer:sampleBuffer ofType:AVMediaTypeAudio];
            }

        }

        CFRelease(sampleBuffer);        
    });
}

    - (void) writeSampleBuffer:(CMSampleBufferRef)sampleBuffer ofType:(NSString *)mediaType
    {
        CMTime presentationTime = CMSampleBufferGetPresentationTimeStamp(sampleBuffer);

        if ( assetWriter.status == AVAssetWriterStatusUnknown ) {

            if ([assetWriter startWriting]) {
                [assetWriter startSessionAtSourceTime:presentationTime];
            } else {
                NSLog(@"Error writing initial buffer");
            }
        }

        if ( assetWriter.status == AVAssetWriterStatusWriting ) {

            if (mediaType == AVMediaTypeVideo) {
                if (assetWriterVideoIn.readyForMoreMediaData) {

                    if (![assetWriterVideoIn appendSampleBuffer:sampleBuffer]) {
                        NSLog(@"Error writing video buffer");
                    }
                }
            }
            else if (mediaType == AVMediaTypeAudio) {
                if (assetWriterAudioIn.readyForMoreMediaData) {

                    if (![assetWriterAudioIn appendSampleBuffer:sampleBuffer]) {
                        NSLog(@"Error writing audio buffer");
                    }
                }
            }
        }
    }

来源：https://stackoverflow.com/questions/8058891/avcapturesession-with-multiple-outputs

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ios

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avcapturesession