feat(capcut): 合并同类型轨道并优化音频/字幕边界裁剪

在同步到本地剪映后新增轨道合并功能，将因降级添加导致的多条同类型轨道合并为单条。同时修复音频和字幕添加时可能跨场景重叠的问题，将 end 裁剪到 slot 边界。

.claude/skills/video-from-script/scripts/capcut_assemble.js

@@ -25,6 +25,7 @@ const {
   addImages, addVideos, addSlotsLocally,
   addVoiceover, addBGM,
   addSubtitles,
+  consolidateTracks,
   addEffects, addFilter,
 } = require('./lib/capcut-tracks')
 const { saveManifest } = require('./lib/pipeline-utils')
@@ -229,7 +230,7 @@ async function assemble(args) {
 
   const steps = []
   if (mode === 'images') steps.push('upload')
-  steps.push('draft', 'materials', 'kenburns', 'audio_oss', 'voiceover', 'audio', 'subtitles', 'effects', 'filter', 'save', 'sync')
+  steps.push('draft', 'materials', 'kenburns', 'audio_oss', 'voiceover', 'audio', 'subtitles', 'effects', 'filter', 'save', 'sync', 'consolidate')
   const totalSteps = steps.length
   let step = 0
 
@@ -407,6 +408,10 @@ async function assemble(args) {
   await syncToLocalJianying(draftUrl, draftId, totalDurationUs)
   console.log('   同步完成\n')
 
+  // -- 合并同类型轨道（TTS 逐条降级时每条独占一个轨道）--
+  step++; console.log(`[${step}/${totalSteps}] 合并同类型轨道...`)
+  consolidateTracks(draftId)
+
   // -- 视频轨道 slot 写入（在 syncToLocalJianying 之后执行，此时本地草稿文件已存在）--
   if (mode !== 'images') {
     step++; console.log(`[${step}/${totalSteps}] 写入视频轨道时间线...`)

.claude/skills/video-from-script/scripts/lib/capcut-tracks.js

@@ -458,6 +458,74 @@ function generateUUID() {
   })
 }
 
+// ============================================================================
+// 本地轨道合并 — 将同一类型的多个轨道合并为一个
+// 背景：远端 add_audios / add_captions 每次调用都会创建新轨道。
+//       批量添加失败降级为逐条调用时，会导致每条 segment 独占一个轨道。
+//       此函数在 sync 后读取本地 draft_content.json，合并同类型轨道。
+// ============================================================================
+
+function consolidateTracks(draftId) {
+  const jianyingPath = getConfig().jianyingDraftPath
+  const draftPath = path.join(jianyingPath, draftId, 'draft_content.json')
+  if (!fs.existsSync(draftPath)) {
+    console.log('   本地草稿不存在，跳过轨道合并')
+    return
+  }
+
+  let draft
+  try {
+    draft = JSON.parse(fs.readFileSync(draftPath, 'utf-8'))
+  } catch {
+    console.log('   draft_content.json 读取失败，跳过轨道合并')
+    return
+  }
+
+  const tracks = draft.tracks || []
+  for (const trackType of ['audio', 'text']) {
+    const sameTypeTracks = tracks.filter(t => t.type === trackType && t.segments && t.segments.length > 0)
+    if (sameTypeTracks.length <= 1) continue
+
+    // 以第一个轨道为主，将其他轨道的 segments 合并进来
+    const primary = sameTypeTracks[0]
+    for (let i = 1; i < sameTypeTracks.length; i++) {
+      primary.segments.push(...sameTypeTracks[i].segments)
+      sameTypeTracks[i].segments = []
+    }
+
+    // 去重：同 start 只保留第一个（批量失败→逐条降级时首段会重复）
+    const seen = new Set()
+    const deduped = []
+    for (const seg of primary.segments) {
+      const key = seg.target_timerange?.start ?? seg.start_time ?? null
+      if (key == null || seen.has(key)) continue
+      seen.add(key)
+      deduped.push(seg)
+    }
+    const dupCount = primary.segments.length - deduped.length
+    primary.segments = deduped
+
+    // 按 start 排序
+    primary.segments.sort((a, b) => {
+      const aStart = a.target_timerange?.start ?? a.start_time ?? 0
+      const bStart = b.target_timerange?.start ?? b.start_time ?? 0
+      return aStart - bStart
+    })
+
+    console.log(`   已合并 ${sameTypeTracks.length} 条 ${trackType} 轨道 → 1 条 (${primary.segments.length} 段)${dupCount > 0 ? ` 去重 ${dupCount} 段` : ''}`)
+  }
+
+  // 移除空轨道（segments 为空的非 video 轨道）
+  draft.tracks = tracks.filter(t => {
+    if (t.type === 'video') return true
+    if (t.type === 'effect' || t.type === 'filter') return true
+    return t.segments && t.segments.length > 0
+  })
+
+  fs.writeFileSync(draftPath, JSON.stringify(draft, null, 2), 'utf-8')
+  triggerDirScan(path.dirname(draftPath))
+}
+
 const { execFile } = require('child_process')
 
 function triggerDirScan(dir) {
@@ -484,33 +552,36 @@ async function addVoiceover(draftUrl, inputDir, items, timeline, audioUrls = {})
     if (!item.audio) continue
 
     if (item.segments && item.segments.length > 0) {
-      // 使用 segments 精确添加
+      // 使用 segments 精确添加，end 裁剪到 slot 边界防止跨场景重叠
       for (const seg of item.segments) {
         if (!seg.audio || seg.error) continue
         const audioUrl = seg.audio.startsWith('http')
           ? seg.audio
           : (audioUrls[seg.audio] || path.resolve(inputDir, seg.audio))
-        const segDurUs = Math.round(seg.duration * US)
         const segStartUs = tl.start + Math.round(seg.startOffset * US)
+        const segEndUs = Math.min(segStartUs + Math.round(seg.duration * US), tl.end)
+        const actualDurUs = segEndUs - segStartUs
         segmentsFlat.push({
           audio_url: audioUrl,
           start: segStartUs,
-          end: segStartUs + segDurUs,
+          end: segEndUs,
-          duration: segDurUs,
+          duration: actualDurUs,
           volume: 1.0,
         })
       }
     } else {
-      // 降级：整段添加
+      // 降级：整段添加，end 裁剪到 slot 边界
       const audioUrl = item.audio.startsWith('http')
         ? item.audio
         : (audioUrls[item.audio] || path.resolve(inputDir, item.audio))
       const audioDurUs = item.audioDuration ? item.audioDuration * US : tl.duration
+      const endUs = Math.min(tl.start + audioDurUs, tl.end)
+      const actualDurUs = endUs - tl.start
       segmentsFlat.push({
         audio_url: audioUrl,
         start: tl.start,
-        end: tl.start + audioDurUs,
+        end: endUs,
-        duration: audioDurUs,
+        duration: actualDurUs,
         volume: 1.0,
       })
     }
@@ -598,15 +669,15 @@ async function addSubtitles(draftUrl, items, timeline, style = {}, split = false
     const tl = timeline[i]
 
     if (split && item.segments && item.segments.length > 0) {
-      // 精确字幕模式：使用 segments 实测时长，逐段添加字幕
+      // 精确字幕模式，end 裁剪到 slot 边界防止跨场景重叠
       for (const seg of item.segments) {
         if (seg.error || !seg.text) continue
         const segStartUs = tl.start + Math.round(seg.startOffset * US)
-        const segDurUs = Math.round(seg.duration * US)
+        const segEndUs = Math.min(segStartUs + Math.round(seg.duration * US), tl.end)
 
         const cap = {
           start: segStartUs,
-          end: segStartUs + segDurUs,
+          end: segEndUs,
           text: seg.text,
         }
 
@@ -819,6 +890,7 @@ module.exports = {
   addKeywordOverlays,
   addSlots,
   addSlotsLocally,
+  consolidateTracks,
   addEffects,
   addFilter,
 }