Whisper's 30-Second Limit Caused 4x Speech Slowdown in Voice Conversion App
A developer building a voice conversion app discovered that long recordings were being reproduced at drastically slower speeds in the output audio. The root cause was traced to OpenAI's Whisper encoder, which processes audio by fixing input to a 30-second log-mel spectrogram and discards anything beyond that limit. When a 131-second recording was fed into the pipeline, Whisper captured only the first 30 seconds of semantic content, which the length regulator then stretched to fill the full 131-second duration — resulting in roughly 4.4x slower speech. Short audio clips were unaffected because they fell within the 30-second window and required no stretching. The recommended fix is to split long audio into 30-second chunks, process each through Whisper separately, and concatenate the resulting feature sequences.
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