Your internet connection may not be fast enough for High Definition (HD), or there may be other devices using the same internet connection and taking up your bandwidth.聽
成人论坛 iPlayer uses technology called Adaptive Bit Rate (ABR) that can reduce or increase the video quality depending on your available internet speed. So if your internet connection is slow or being used by several devices, it will play the video at a lower quality to fit the available bandwidth, rather than buffering.
You can find out how to check your internet speed on the聽How can I check if my internet connection is fast enough for 成人论坛 iPlayer? page. For help with buffering, check the聽What can I do to help with buffering or playback problems? page.