From 628466b06625758b1a7a46ce06ebf0d4d102cfc1 Mon Sep 17 00:00:00 2001
From: Achyut Krishna Byanjankar <achyut.benz@gmail.com>
Date: Sat, 18 Apr 2026 17:08:16 -0700
Subject: [PATCH] whisper : skip decoding of zero-filled chunks on
 forced-language path
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When a specific language is forced (e.g. -l ru, -l es) and a 30-second
decoder window is entirely zero-valued, whisper emits language-specific
fallback tokens (bracketed music tags like [Música], fake subtitle-editor
credits on -l ru). The auto-detect path handles silent chunks naturally.

Add a chunk-level zero-PCM check at the top of the seek loop inside
whisper_full_with_state. When the current window is all-zero and the
caller forced a language, emit a single [BLANK_AUDIO] segment for that
chunk and advance without running the encoder or decoder. Matches the
approach endorsed in PR #1588 review ("skip entire segments when
silence is detected"), using zero-PCM as a stricter and language-
independent signal than no_speech_prob.

The caller's original language intent is captured before the auto-
detect block overwrites params.language, so the guard only fires when
the user explicitly requested a specific language; auto-detect paths
are unchanged.

Fixes #1724 (residual hallucination on forced-language silence chunks
not addressed by #2629)
---
 src/whisper.cpp | 45 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

diff --git a/src/whisper.cpp b/src/whisper.cpp
index 2f356da0..3f65c412 100644
--- a/src/whisper.cpp
+++ b/src/whisper.cpp
@@ -6800,6 +6800,14 @@ int whisper_full_with_state(
 
     result_all.clear();
 
+    // Capture whether the caller forced a specific language before
+    // the auto-detect block below overwrites params.language.
+    // ref: https://github.com/ggml-org/whisper.cpp/issues/1724
+    const bool language_was_forced_by_caller = (params.language != nullptr
+        && strlen(params.language) > 0
+        && strcmp(params.language, "auto") != 0
+        && !params.detect_language);
+
     if (n_samples > 0) {
         // compute log mel spectrogram
         if (whisper_pcm_to_mel_with_state(ctx, state, samples, n_samples, params.n_threads) != 0) {
@@ -7009,6 +7017,43 @@ int whisper_full_with_state(
             break;
         }
 
+        // Chunk-level zero-silence guard. When the current 30-second
+        // window is entirely zero-valued and the caller forced a
+        // specific language, emit a [BLANK_AUDIO] segment and advance
+        // without running the encoder/decoder. Without this, forced-
+        // language decoding of silent chunks emits language-specific
+        // fallback tokens (e.g. "[Музыка]" on -l ru, "[Música]" on
+        // -l es) or model-trained subtitle-credit phrases on -l ru.
+        // This matches the approach endorsed by the maintainer in
+        // PR #1588 review ("skip entire segments when silence is
+        // detected"), using zero-PCM as a stricter signal than the
+        // language-dependent no_speech_prob.
+        // ref: https://github.com/ggml-org/whisper.cpp/issues/1724
+        if (language_was_forced_by_caller && samples != nullptr) {
+            const int chunk_start = seek * (WHISPER_SAMPLE_RATE / 100);
+            const int chunk_end = std::min(n_samples, chunk_start + WHISPER_CHUNK_SIZE * WHISPER_SAMPLE_RATE);
+            if (chunk_start < chunk_end) {
+                bool chunk_is_zero = true;
+                for (int i = chunk_start; i < chunk_end; ++i) {
+                    if (samples[i] != 0.0f) {
+                        chunk_is_zero = false;
+                        break;
+                    }
+                }
+                if (chunk_is_zero) {
+                    WHISPER_LOG_INFO("%s: chunk at seek=%d is zero-filled with forced language %s; emitting blank-audio and skipping decode (ref: #1724)\n", __func__, seek, params.language);
+                    const int64_t t0 = seek;
+                    const int64_t t1 = (int64_t) chunk_end * 100 / WHISPER_SAMPLE_RATE;
+                    result_all.push_back({ t0, 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);
+                    }
+                    seek += WHISPER_CHUNK_SIZE * 100;
+                    continue;
+                }
+            }
+        }
+
         if (params.encoder_begin_callback) {
             if (params.encoder_begin_callback(ctx, state, params.encoder_begin_callback_user_data) == false) {
                 WHISPER_LOG_ERROR("%s: encoder_begin_callback returned false - aborting\n", __func__);