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whisper : guard against hallucinations on zero-filled input (#1881) #3762

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whisper : guard against hallucinations on zero-filled input (#1881) #3762

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33 changes: 33 additions & 0 deletions src/whisper.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -6800,6 +6800,39 @@ int whisper_full_with_state(

result_all.clear();

// Guard against hallucinations on zero-filled input when a specific
// language is forced (e.g. -l ru, -l es). The auto-detect path
// naturally emits "[BLANK_AUDIO]" for silent input, but forcing a
// language biases the decoder toward language-specific fallback
// tokens (Cyrillic music tags on -l ru, "[Música]" on -l es, etc.).
// Detect zero-filled input up-front in the forced-language case and
// emit a single [BLANK_AUDIO] segment spanning the input duration,
// matching the auto-detect path's output shape.
// The auto-detect case is intentionally left untouched.
// ref: https://github.com/ggml-org/whisper.cpp/issues/1881
const bool language_is_forced = (params.language != nullptr
&& strlen(params.language) > 0
&& strcmp(params.language, "auto") != 0
&& !params.detect_language);
if (n_samples > 0 && language_is_forced) {
bool is_all_zero = true;
for (int i = 0; i < n_samples; ++i) {
if (samples[i] != 0.0f) {
is_all_zero = false;
break;
}
}
if (is_all_zero) {
WHISPER_LOG_INFO("%s: input is zero-filled with forced language %s; emitting blank-audio segment (ref: #1881)\n", __func__, params.language);
const int64_t t1 = (int64_t) n_samples * 100 / WHISPER_SAMPLE_RATE;
result_all.push_back({ 0, t1, " [BLANK_AUDIO]", 1.0f, {}, false });
if (params.new_segment_callback && !ctx->params.dtw_token_timestamps) {
params.new_segment_callback(ctx, state, 1, params.new_segment_callback_user_data);
}
return 0;
}
}

if (n_samples > 0) {
// compute log mel spectrogram
if (whisper_pcm_to_mel_with_state(ctx, state, samples, n_samples, params.n_threads) != 0) {
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