使用GPUImageVideoCamera和GPUImageMovieWriter ,视频前面一帧有白屏(或者黑屏帧)
主要原因是音频采集会更快。

• 参考代码1

 #import "GPUImageContext.h"

 #import "GLProgram.h"

 #import "GPUImageFilter.h"

+static BOOL allowWriteAudio = NO;

 

/////////////////////////////////////////////////////////

- (void)startRecording;
{
    + allowWriteAudio = NO;

    alreadyFinishedRecording = NO;

    startTime = kCMTimeInvalid;
}

//////////////////////////////////////////////////////////


- (void)finishRecordingWithCompletionHandler:(void (^)(void))handler;

 - (void)processAudioBuffer:(CMSampleBufferRef)audioBuffer;
 {
        + if (!allowWriteAudio) {
        + return;
        + }
 if (!isRecording)
 {
       return;

////////////////////////////////////////////////////////////////////////////////////

 - (void)processAudioBuffer:(CMSampleBufferRef)audioBuffer;
 {
   if (![assetWriterAudioInput appendSampleBuffer:audioBuffer])

   NSLog(@"Problem appending audio buffer at time: %@", CFBridgingRelease(CMTimeCopyDescription(kCFAllocatorDefault, currentSampleTime)));

  + allowWriteAudio = YES;

• 上述改法可能也有bug，参考另外的改法
  参考代码2

• [self.videoCamera addAudioInputsAndOutputs];
  调用GPUImageVideoCamera这句话就可以避免一开始黑屏