Buffer sample most function

Case 1: Sampler finishes before source stream
source:  ---1--2--3--4--5--6--7--8->
sampler: -x------x--------x--x--|
result:  --------a--------b--c--d|
  a = [1,2]
  b = [3,4,5]
  c = [6]
  d = [7]

Case 2: Sampler finishes after source stream
source:  ---1--2--3--4--5--6--7--8-|
sampler: -x------x--------x-x---------x->
result:  --------a--------b-c------d|
  a = [1,2]
  b = [3,4,5]
  c = [6]
  d = [7,8]