使用AVAssetWriter录制视频:第一帧是黑色的

Question

我正在录制视频(用户也可以只切换到音频)AVAssetWriter.我在应用程序启动时开始录制.但是第一帧是黑色(或非常暗).当我从音频切换到视频时也会发生这种情况.感觉就像AVAssetWriter和/或AVAssetWriterInput尚未准备好记录.我怎么能避免这个？

我不知道这是否有用,但我也用a GLKView来显示视频.

func start_new_record(){
    do{
        try self.file_writer=AVAssetWriter(url: self.file_url!, fileType: AVFileTypeMPEG4)
        if video_on{
            if file_writer.canAdd(video_writer){
                file_writer.add(video_writer)
            }
        }
        if file_writer.canAdd(audio_writer){
            file_writer.add(audio_writer)
        }
    }catch let e as NSError{
        print(e)
    }
}

func captureOutput(_ captureOutput: AVCaptureOutput!, didOutputSampleBuffer sampleBuffer: CMSampleBuffer!, from connection: AVCaptureConnection!){
    guard is_recording else{
        return
    }

    guard CMSampleBufferDataIsReady(sampleBuffer) else{
        print("data not ready")
        return
    }

    guard let w=file_writer else{
        print("video writer nil")
        return
    }

    if w.status == .unknown && start_recording_time==nil{
        if (video_on && captureOutput==video_output) || (!video_on && captureOutput==audio_output){
            print("START RECORDING")
            file_writer?.startWriting()
            start_recording_time=CMSampleBufferGetPresentationTimeStamp(sampleBuffer)
            file_writer?.startSession(atSourceTime: start_recording_time!)
        }else{
            return
        }
    }

    if w.status == .failed{
        print("failed /", w.error ?? "")
        return
    }

    if captureOutput==audio_output{
        if audio_writer.isReadyForMoreMediaData{
            if !video_on || (video_on && video_written){
                audio_writer.append(sampleBuffer)
                //print("write audio")
            }
        }else{
            print("audio writer not ready")
        }
    }else if video_output != nil && captureOutput==video_output{
        if video_writer.isReadyForMoreMediaData{
            video_writer.append(sampleBuffer)
            if !video_written{
                print("added 1st video frame")
                video_written=true
            }
        }else{
            print("video writer not ready")
        }
    }
}

Answer 1

SWIFT 4

SOLUTION #1:

I resolved this by calling file_writer?.startWriting() as soon as possible upon launching the app. Then when you want to start recording, do the file_writer?.startSession(atSourceTime:...).

完成记录并调用finishRecording时，当您获得表明已完成的回调时，再次设置一个新的书写会话。

解决方案2：

我通过在调用AVAssetWriter.startSession时将启动时间增加了半秒来解决此问题，如下所示：

start_recording_time = CMSampleBufferGetPresentationTimeStamp(sampleBuffer)
let startingTimeDelay = CMTimeMakeWithSeconds(0.5, 1000000000)
let startTimeToUse = CMTimeAdd(start_recording_time!, startingTimeDelay)

file_writer?.startSession(atSourceTime: startTimeToUse)

解决方案＃3：

这里一个更好的解决方案是记录您收到的第一帧的时间戳并决定写入，然后以此开始会话。然后，您不需要任何延迟：

//Initialization, elsewhere:

var is_session_started = false
var videoStartingTimestamp = CMTime.invalid

// In code where you receive frames that you plan to write:

if (!is_session_started) {
    // Start writing at the timestamp of our earliest sample
    videoStartingTimestamp = currentTimestamp
    print ("First video sample received: Starting avAssetWriter Session: \(videoStartingTimestamp)")
    avAssetWriter?.startSession(atSourceTime: videoStartingTimestamp)

    is_session_started = true
}

// add the current frame
pixelBufferAdapter?.append(myPixelBuffer, withPresentationTime: currentTimestamp)

Answer 2

好吧，愚蠢的错误...

启动应用程序时，我初始化我的AVCaptureSession，添加输入、输出等。我只是调用得start_new_record太早了，就在commitConfiguration我的捕获会话被调用之前。

至少我的代码可能对某些人有用。