Audio desync using AVPlayerItemVideooutput on iOS

On iOS, I use AVPlayer to stream videos. I ceate an AVPlayerItem from URL, then I add a AVPlayerItemVideoOutput. During playback, I do:

auto t = [self.player.currentItem currentTime];
AVPlayerItemVideoOutput * p=self.player_item_output;
if( [p hasNewPixelBufferForItemTime:t] )
{
  CVPixelBufferRef b=[p copyPixelBufferForItemTime:[self.player.currentItem currentTime] itemTimeForDisplay:nil];
  ...

The audio seems to play on its own and is nicely synched with the video frames I displayfrom the pixel buffer, even when the connection is less than perfect... except that sometimes it does desync.

Do I need to do anything to make sure audio stays syched at all times, or should I dismiss these rare desynchs as glitches that can not be fixed?

Thanks,

Emil