This usually happens for 2 reasons
- Using a cheap copy of the official Apple Lightening to AV adaptor
- Not enough wifi bandwidth to stream to an Apple TV
If you're streaming to an Apple TV from your iPhone or iPad, download the video first as this places far less stress on your local network. Remember, if you have a 4th Generation Apple TV or newer, please download it directly from the Apple TV.
You need to use the proper/correct Apple Lightning to AV Adaptor. Third party adaptors that claim to do the same ting can't, because Apple has exclusive access to the required technology. Our own research found that even though the adaptor was plugging into the phone and the TV, it was actually streaming the signal via wifi. This would explain the really poor performance.