feat: allow selecting text SRT in SYNC command, using other for timestamp

merge_srt.py

@@ -64,14 +64,19 @@ def read_commands(filename):
                 continue
             commands.append(('MAP', text_source, text_start, time_source, time_start, count))
         elif command == 'SYNC':
-            if len(parts) != 3:
+            if len(parts) != 4:
                 continue
             try:
-                source1_index = int(parts[1])
-                source2_index = int(parts[2])
+                text_source = int(parts[1])
+                text_index = int(parts[2])
+                time_index = int(parts[3])
+                if text_source not in (1, 2):
+                    continue
+                if text_index < 1 or time_index < 2:
+                    continue
             except (ValueError, AttributeError):
                 continue
-            commands.append(('SYNC', source1_index, source2_index))
+            commands.append(('SYNC', text_source, text_index, time_index))
         else:
             continue
     return commands
@@ -151,19 +156,25 @@ if __name__ == '__main__':
                     'text': text_entry['text'],
                 })
         elif cmd[0] == 'SYNC':
-            source1_index, source2_index = cmd[1:]
-            if source1_index < 2 or source1_index > len(srt1) or source2_index < 1 or source2_index > len(srt2):
-                print(f"Skipping invalid SYNC command: source1 index {source1_index} must be >=2 and <= {len(srt1)}, source2 index {source2_index} must be >=1 and <= {len(srt2)}")
+            text_source, text_index, time_index = cmd[1:]
+            text_list = srt1 if text_source == 1 else srt2
+            time_list = srt2 if text_source == 1 else srt1
+            text_start_idx = text_index - 1
+            time_start_idx = time_index - 1
+            prev_time_idx = time_start_idx - 1
+            if (text_start_idx < 0 or text_start_idx >= len(text_list) or
+                time_start_idx < 1 or prev_time_idx < 0 or time_start_idx >= len(time_list)):
+                print(f"Skipping invalid SYNC command: text index {text_index} must be >=1 and <= {len(text_list)}, time index {time_index} must be >=2 and <= {len(time_list)}")
                 continue
-            entry_prev = srt1[source1_index - 2]
-            entry1 = srt1[source1_index - 1]
-            entry2 = srt2[source2_index - 1]
-            delta = compute_delta(entry_prev['timestamp'], entry1['timestamp'])
-            new_ts = add_delta_to_timestamp(entry2['timestamp'], delta)
+            text_entry = text_list[text_start_idx]
+            time_entry = time_list[time_start_idx]
+            prev_time_entry = time_list[prev_time_idx]
+            delta = compute_delta(prev_time_entry['timestamp'], time_entry['timestamp'])
+            new_ts = add_delta_to_timestamp(time_entry['timestamp'], delta)
             output.append({
                 'index': len(output) + 1,
                 'timestamp': new_ts,
-                'text': entry2['text'],
+                'text': text_entry['text'],
             })
 
     if output_filename == '-':