stale transcripts getting added to next user turn when using min_interrupt_words

[0xnktd]

Bug Description

When using min_interruption_words to prevent agent interruptions from short backchannel utterances, these transcripts are buffered and incorrectly included in the next user turn, causing confusion for the LLM.

Problem Details

• Agent is speaking and user says a backchannel (e.g., "uh-huh", "okay")
• If the utterance has fewer words than min_interruption_words, the agent continues speaking
• The transcript gets stored in AudioRecognition buffers (_audio_transcript, _audio_interim_transcript)
• When the agent finishes speaking, these buffered transcripts appear in the next user turn
• The LLM receives stale backchannel transcripts as if they were new user input

Expected Behavior

Backchannel utterances that don't meet the interruption threshold should be discarded and not included in subsequent user turns.

Reproduction Steps

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- Sample code snippet, or a GitHub Gist link -

Operating System

Linux

Models Used

No response

Package Versions

livekit-agents==1.3.9

Session/Room/Call IDs

No response

Proposed Solution

Implement a method in AudioRecognition class to clear stale transcripts that are older than a threshold time.

Additional Context

No response

Screenshots and Recordings

No response

[longcw]

Backchannel utterances that don't meet the interruption threshold should be discarded and not included in subsequent user turns

for now there is no way to know if the transcription is backchannel utterance or actual user input, I don't think it makes sense to drop it just because they are shorter than the interruption threshold.

btw, we are going to release a barge-in detector in next versions that probably helpful for your use case #4319

[0xnktd]

You're right - without semantic understanding, we can't reliably distinguish backchannels from actual input. The barge-in detector sounds promising for addressing this. Thanks for the reply.

[0xnktd]

Hi @longcw is there any ETA on when the barge-in detector is planned to be released?

[davidzhao]

please follow the above PR.