Why would you want it to buffer? The only reason a video buffers is when it's trying to have the quality and playback "normal" but the connection might be slow or trying to catch up. So instead of play, pause, play, pause.. It buffers for a few seconds and grabs some of the video. So it can then play and stream the video but the stream is ahead of where you are watching now.
On wifi usually a connection can keep up with the video so.. It just starts playing.
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