Bug: MovingAverage.reset() does not clear internal history buffer, causing incorrect averages after reset

[kuishou68]

Bug Description

MovingAverage.reset() in livekit-agents/livekit/agents/utils/moving_average.py resets _count and _sum to zero but does not clear the _hist ring-buffer. This causes stale values from before the reset to corrupt the moving average once the window fills up again.

Root Cause

def reset(self) -> None:
    self._count = 0
    self._sum = 0
    # BUG: self._hist is not cleared!

After reset(), as add_sample() is called:

• _count increments from 0, _sum is rebuilt correctly until the window is full.
• Once _count > len(self._hist), the code subtracts self._hist[index] from _sum to evict the oldest entry. But _hist[index] still contains the pre-reset value, so the sum is incorrectly reduced by that stale value.

Fix

Clear _hist in reset():

def reset(self) -> None:
    self._hist = [0.0] * len(self._hist)
    self._count = 0
    self._sum = 0.0

Impact

MovingAverage is used in metrics tracking across the agents framework. Incorrect averages after a reset can lead to skewed performance metrics and incorrect adaptive behaviour.

[kuishou68]

A fix has been submitted in PR:

[kuishou68]

A fix has been submitted in PR #5522. The patch adds self._hist = [0.0] * len(self._hist) as the first line of reset(), ensuring the ring-buffer is cleared alongside _count and _sum.

[longcw]

see the comment here #5522 (comment), the hist values are all overwritten when count > len(hist) so it should be fine actually