Record video from camera with AVAssetWriter

gistfile1.txt

Sometimes, for some reason, you have to use AVAssetWriter to record videos from camera instead of using movile file output.
I had experienced some issue by that recording method due to lacking of tutorial and SO questions :))

Noted for everyone who met the issue: black first frame

if (CMSampleBufferDataIsReady(sampleBuffer)) {
  if (videoWriter.status != AVAssetWriterStatusWriting) {
    CMTime startTime = CMSampleBufferGetPresentationTimeStamp(sampleBuffer);
    [videoWriter startWriting];
    [videoWriter startSessionAtSourceTime:startTime];
  }
  if (writerInput.readyForMoreMediaData == YES) {
    [writerInput appendSampleBuffer:sampleBuffer];
  }
}

I had used if (writerInput.readyForMoreMediaData == YES) { before, so it leads to first frame can not be appended.