When video is buffering, why does the percentage sometimes decrease?

[Mark T]

I thought buffering meant downloading the video in advance so that you can have constant play. If it has downloaded the video why does it suddenly lose a percentage?

 

[skip0110]

The buffer size is based on the download rate. If your connection is slower, a bigger buffer needs to be filled so that the video can play through without stoppping.

Media players monitor the rate at which the video is downloading to determine the buffer size. If a video starts out downloading fast, the buffer size will be small and the percentage will increase quickly. If the rate drops during the buffering, the player will lengthen the buffer size, meaning that the percent buffered will drop.

HTH