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fix: reuse BytesIO buffer to avoid reallocation in StreamBuffer #4507

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fix: reuse BytesIO buffer to avoid reallocation in StreamBuffer #4507

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8 changes: 7 additions & 1 deletion livekit-agents/livekit/agents/utils/codecs/decoder.py
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Original file line number Diff line number Diff line change
Expand Up @@ -98,7 +98,13 @@ def read(self, size: int = -1) -> bytes:
if data:
# shrink the buffer to remove already-read data
remaining = self._buffer.read()
self._buffer = io.BytesIO(remaining)

# Reuse the same buffer instead of reallocating
self._buffer.seek(0)
self._buffer.truncate()
self._buffer.write(remaining)
self._buffer.seek(0)
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@davidzhao davidzhao Jan 12, 2026

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I don't think this works.

would future bytes be written at 0? overwriting remaining? reading and writing are happening at the same position, which isn't what we want

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@darshankparmar darshankparmar Jan 12, 2026

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I don't think this works.

would future bytes be written at 0? overwriting remaining? reading and writing are happening at the same position, which isn't what we want

Thanks for the review. After a deeper look, you’re right.

While the truncate-based approach reduces allocations, it relies on implicit BytesIO cursor behavior and isn’t robust enough for a concurrency primitive.
Alternative designs (e.g. ring buffers) would break PyAV’s file-like contract or require a larger redesign.

I’ll revert this change and keep the existing behavior for correctness.


return data

if self._eof:
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