fix: time selection click and shiftclick

app/core/dsp_utils.py

@@ -80,6 +80,49 @@ def apply_micro_fade(segment: AudioSegment, fade_duration_ms: int = 50) -> Audio
     return segment
 
 
+def apply_micro_crossfade(original: np.ndarray, edited: np.ndarray, start_sample: int, fade_len_ms: int = 10, sr: int = 44100) -> np.ndarray:
+    """
+    Áp dụng bộ lọc mờ biên Micro-crossfade (10ms) tại hai đầu điểm ráp nối
+    để triệt tiêu tiếng click/pop khi Apply & Merge Back (22_CLIENT_DESK.md §2.2).
+    
+    Output(t) = (1 - alpha(t)) * Original(t) + alpha(t) * Edited(t - T_start)
+    """
+    fade_samples = int((fade_len_ms / 1000.0) * sr)
+    if fade_samples <= 0 or len(original) == 0:
+        return edited
+
+    output = np.copy(original)
+    edited_len = len(edited)
+    end_sample = min(len(original), start_sample + edited_len)
+    actual_len = end_sample - start_sample
+
+    if actual_len <= 0:
+        return output
+
+    fade_in_len = min(fade_samples, actual_len)
+    fade_out_len = min(fade_samples, actual_len)
+
+    alpha_in = np.linspace(0.0, 1.0, fade_in_len)
+    alpha_out = np.linspace(1.0, 0.0, fade_out_len)
+
+    output[start_sample:end_sample] = edited[:actual_len]
+
+    # Fade in at start splice point
+    for i in range(fade_in_len):
+        idx = start_sample + i
+        if idx < len(original):
+            output[idx] = (1.0 - alpha_in[i]) * original[idx] + alpha_in[i] * edited[i]
+
+    # Fade out at end splice point
+    for i in range(fade_out_len):
+        idx = end_sample - fade_out_len + i
+        edit_idx = actual_len - fade_out_len + i
+        if idx < len(original) and edit_idx < len(edited):
+            output[idx] = alpha_out[i] * edited[edit_idx] + (1.0 - alpha_out[i]) * original[idx]
+
+    return output
+
+
 def generate_peak_waveform(file_path: str, num_peaks: int = 800) -> dict:
     """
     Tạo dữ liệu peak waveform cho hiển thị đồ thị sóng âm trên Frontend.