I've definitely encountered this issue before. It's annoying - I spent some time trying to investigate why it occurs but it's sporadic enough that I just looked to mitigate it some other way.

Here's a low-tech solution: after the movieWriter is finished recording, start an AVAssetExportSession with the newly completely video URL, chop some "buffer time" off the video, then save it back to disk. I find that removing a CMTime duration of CMTimeMake(1,10) off both the start and end of the movieWriter video removes all black frame artifacts. YMMV. I'd recommend maybe using movieWriter finishRecordingWithCompletionHandler, and then in the completion block make a call to whatever method does the "buffer time" trimming.

If you notice, Apple's stock Camera app (when taking a video) chops off a bit of time from the beginning of a video after you finish recording. I'm not saying it's necessarily because of an issue like this, but just wanted to mention it to illustrate that it can indeed be a lot of data to deal with.

I leave it to more interested minds to discover the "why" of this issue and engineer a better solution.

Thanks for your input mate - what you suggest (chopping the frames off) is definitely in for Plan B. I never noticed the chopping off on Apple's stock camera app, interesting!

Is definitely worth finding out the reason behind this behavior and a possible solution. Will continue to look into it myself.

videoCamera.audioEncodingTarget = movieWriter - this is your problem. It's very expensive operation.

I experienced the same issue, anyone else has solution?

I think I found the reason, I look into the file GPUImageVideoCamera.m, the GPUImageVideoCamera process frames, There is a semaphore named frameRenderingSemaphore, at line 951. It will wait this semaphore, when the process is not finished,It will drop the frames. and I think GPUImage does not change CMTime of CMSampleBufferRef. I do not have some solution, To solute this problem, You may rewrite this class.

No luck with this and as much as I have tried to push it back, its quite incorrect user-experience wise to have these black frames you cannot control. Anyone with a solution, please do let know.

I do have the same problem and can't resolved it.

I met the same issue. Any solution now?

The problem is that the audio buffer is written before the video buffer.
Fix:

Inside GPUImageMovieWriter.m
add code:

static BOOL allowWriteAudio = NO;

- (void)startRecording;
{
  ...
  allowWriteAudio = NO;
}

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

- (void)newFrameReadyAtTime:(CMTime)frameTime atIndex:(NSInteger)textureIndex;
{
  ...
  if (![assetWriterPixelBufferInput appendPixelBuffer:pixel_buffer withPresentationTime:frameTime])
    NSLog(@"Problem appending pixel buffer at time: %@", CFBridgingRelease(CMTimeCopyDescription(kCFAllocatorDefault, frameTime)));

  allowWriteAudio = YES;   //< add this
  ...
}

Thank you so much KageDev! You're the hero.

hello,can anyOne help me?When i add this code,my video is silent,there is no sound, please help me...

@KageDev e~,it can avoid the black frame at the beginning, but the black frame at the end still occur sometimes.do you know how to solve it?

5c and 4s the black frame at the end still occur

I added a pull request #2410 to fix the black frame issue.

I've got a workaround for this issue. Basically you need to track the first video frame time and the last video frame time. After the movie writer finishes exporting the video file, trim the output file manually based on the time range from the first frame time to the last frame time.

@zmzhuai i tried you code, great! avoid the end frame! so cool.(attention, when use movie writer do other things ,like edit video , add music , the audio will lost, so i add a var ,use this only when record video.)