根据AI的提示和我自己发现的问题，进行修复

Author: Starrah

MaiChartManager/Controllers/Music/MusicTransferController.cs

@@ -582,7 +582,7 @@ public async Task ExportAsMaidata(int id, string assetDir, bool ignoreVideo = fa
             // ignore preview time errors
         }
 
-        var ma2Contents = new Dictionary<int, string[]>();
+        var ma2Contents = new List<(int, string[])>();
 
         // 关于clock_count功能，我决定不走MaiLib了，而是我们自己解析。因为ma2.Compose返回的是裸谱面inote中的内容，没有办法合理的把clock信息插进去。因此，我们自己解析吧。
         // 选用最难的一张有效谱面的MET值作为全曲的&clock_count
@@ -602,7 +602,7 @@ public async Task ExportAsMaidata(int id, string assetDir, bool ignoreVideo = fa
             }
 
             var ma2Content = await System.IO.File.ReadAllLinesAsync(chartPath);
-            ma2Contents[i] = ma2Content;
+            ma2Contents.Add((i, ma2Content));
 
             // 从谱面内容中寻找MET行
             var metLine = ma2Content.FirstOrDefault(it => it.StartsWith("MET\t"));

MaiChartManager/Front/src/views/Charts/ImportCreateChartButton/ImportChartButton/index.tsx

@@ -170,7 +170,14 @@ export default defineComponent({
         let audioPadding = chartPadding - music.first;
 
         await api.SetAudio(music.id, selectedADir.value, { file: music.track, padding: audioPadding, ignoreGapless: !!tempOptions.value.ignoreGapless });
-        if (music.previewTime) await api.SetAudioPreview(music.id, selectedADir.value, music.previewTime);
+        if (music.previewTime) {
+          // 因为&demo_seek和&demo_len都是相对于原始音源的，所以这里的时间必须要扣掉上面SetAudio时应用的padding。
+          // 根据SetAudioApi的定义，padding为正表示歌曲前面被加了空白，因此原本的预览段在新的裁剪后的音频中的位置也要相应后移；padding为负反之。
+          // 因此，直接给startTime和endTime都加上audioPadding即可。
+          music.previewTime.startTime! += audioPadding;
+          music.previewTime.endTime! += audioPadding
+          await api.SetAudioPreview(music.id, selectedADir.value, music.previewTime);
+        }
 
         if (music.movie && !tempOptions.value.disableBga) {
           currentMovieProgress.value = 0;

MaiChartManager/Services/MaidataImportService.cs

@@ -262,23 +262,11 @@ private record AllChartsEntry(string chartText, MaiChart simaiSharpChart);
 
     [GeneratedRegex(@"^(MET\t\d+\t\d+\t\d+\t)(\d+\s*)$", RegexOptions.Multiline)]
     private static partial Regex FirstMetLineRegex();
-
-    private static string replaceGroup2ByRegex(string input, Match match, int value)
-    {
-        if (!match.Success) return input;
-        return string.Concat(
-            input.AsSpan(0, match.Index),
-            match.Groups[1].ValueSpan,
-            value.ToString(CultureInfo.InvariantCulture),
-            input.AsSpan(match.Index + match.Length));
-    }
 
     private static string ApplyClockCountToFirstMetLine(string ma2Content, int clockCount)
     {
-        var clockdefMatch = ClockDefRegex().Match(ma2Content);
-        ma2Content = replaceGroup2ByRegex(ma2Content, clockdefMatch, 96 * clockCount);
-        var metMatch = FirstMetLineRegex().Match(ma2Content);
-        ma2Content = replaceGroup2ByRegex(ma2Content, metMatch, clockCount);
+        ma2Content = ClockDefRegex().Replace(ma2Content, $"${{1}}{96 * clockCount}", 1);
+        ma2Content = FirstMetLineRegex().Replace(ma2Content, $"${{1}}{clockCount}", 1);
         return ma2Content;
     }
 
@@ -439,7 +427,8 @@ public ImportChartResult ImportMaidata(
             // 如果maidata中声明了clock_count，应用之，修改CLOCK_DEF和MET
             if (int.TryParse(maiData.GetValueOrDefault("clock_count"), out var clockCount))
             {
-                shiftedConverted = ApplyClockCountToFirstMetLine(shiftedConverted, clockCount);
+                if (clockCount > 0) shiftedConverted = ApplyClockCountToFirstMetLine(shiftedConverted, clockCount);
+                else errors.Add(new ImportChartMessage("the \"&clock_count\" value in this maidata is invalid thus ignored.", MessageLevel.Warning));
             }
 
             // Just use T_NUM_ALL value in ma2 file