[其他] 谁能告诉我Global percent of torn frames的算法

Clip 1 info:
Length of clip: 3087 frames
Average FPS of clip: 29.94
Percent of torn frames: 1.71
Clip 2 info:
Length of clip: 2152 frames
Average FPS of clip: 30.22
Percent of torn frames: 0.90
Clip 3 info:
Length of clip: 8540 frames
Average FPS of clip: 29.96
Percent of torn frames: 1.26
Clip 4 info:
Length of clip: 2623 frames
Average FPS of clip: 30.72
Percent of torn frames: 0.30

Global percent of torn frames: 2.0
Global average FPS: 30.11

百思不得其解啊，为什么总平均会比任一clip的数据高呢？