Reject extension stitches that are still the original clip.

Xfade and concat copy could exit 0 while writing only part 1; require a longer output and fall back to a re-encode concat of both originals.

server/utils/ffmpeg.ts

@@ -94,33 +94,36 @@ export async function probeHasAudio(filePath: string) {
 
 const XFADE_DURATION = 0.12
 
-async function probeDuration(filePath: string) {
+function parseRate(rate: string) {
-  const out = await runFfprobe([
+  const [num, den] = String(rate || '').split('/').map(Number)
-    '-v', 'error',
+  if (den) return num / den
-    '-show_entries', 'format=duration',
+  const value = Number(rate)
-    '-of', 'default=nokey=1:noprint_wrappers=1',
+  return Number.isFinite(value) && value > 0 ? value : NaN
-    filePath
-  ])
-  const duration = Number(out)
-  if (!Number.isFinite(duration) || duration <= 0) {
-    throw new Error('Could not read video duration')
-  }
-  return duration
 }
 
-async function probeFps(filePath: string) {
+async function probeDuration(filePath: string) {
-  const out = await runFfprobe([
+  const raw = await runFfprobe([
     '-v', 'error',
     '-select_streams', 'v:0',
-    '-show_entries', 'stream=avg_frame_rate,r_frame_rate',
+    '-show_entries', 'stream=duration,nb_frames,r_frame_rate,avg_frame_rate',
-    '-of', 'default=nokey=1:noprint_wrappers=1',
+    '-show_entries', 'format=duration',
+    '-of', 'json',
     filePath
   ])
-  const line = out.split(/\r?\n/).map(item => item.trim()).find(Boolean) || ''
+  const parsed = JSON.parse(raw) as {
-  const [num, den] = line.split('/').map(Number)
+    format?: { duration?: string }
-  if (Number.isFinite(num) && Number.isFinite(den) && den > 0) return num / den
+    streams?: Array<{ duration?: string; nb_frames?: string; r_frame_rate?: string; avg_frame_rate?: string }>
-  const fps = Number(line)
+  }
-  return Number.isFinite(fps) && fps > 0 ? fps : 24
+  const stream = parsed.streams?.[0] || {}
+  const fps = parseRate(stream.avg_frame_rate || '') || parseRate(stream.r_frame_rate || '')
+  const frames = Number(stream.nb_frames)
+  const fromFrames = Number.isFinite(frames) && frames > 0 && Number.isFinite(fps) ? frames / fps : NaN
+  const candidates = [Number(stream.duration), Number(parsed.format?.duration), fromFrames]
+    .filter(value => Number.isFinite(value) && value > 0)
+  if (!candidates.length) {
+    throw new Error('Could not read video duration')
+  }
+  return Math.min(...candidates)
 }
 
 async function probeSize(filePath: string) {
@@ -138,84 +141,100 @@ async function probeSize(filePath: string) {
   }
 }
 
-async function trimLeadingFrame(inputPath: string, outputPath: string) {
+function encodeArgs(outputPath: string, withAudio: boolean) {
-  const fps = await probeFps(inputPath)
-  const hasAudio = await probeHasAudio(inputPath)
   const args = [
-    '-y',
-    '-i', inputPath,
-    '-vf', 'trim=start_frame=1,setpts=PTS-STARTPTS'
-  ]
-  if (hasAudio) {
-    args.push('-af', `atrim=start=${(1 / fps).toFixed(6)},asetpts=PTS-STARTPTS`, '-c:a', 'aac')
-  } else {
-    args.push('-an')
-  }
-  args.push(
-    '-c:v', 'libx264',
-    '-preset', 'fast',
-    '-crf', '17',
-    '-pix_fmt', 'yuv420p',
-    '-movflags', '+faststart',
-    outputPath
-  )
-  await runFfmpeg(args, 180000)
-  if (!existsSync(outputPath)) {
-    throw new Error('FFmpeg did not write the trimmed extension segment')
-  }
-}
-
-async function xfadeStitch(part1Path: string, part2Path: string, outputPath: string) {
-  const [duration1, duration2, fps, size, audio1, audio2] = await Promise.all([
-    probeDuration(part1Path),
-    probeDuration(part2Path),
-    probeFps(part1Path),
-    probeSize(part1Path),
-    probeHasAudio(part1Path),
-    probeHasAudio(part2Path)
-  ])
-  const fade = Math.min(
-    XFADE_DURATION,
-    Math.max(0.04, duration1 - 0.05),
-    Math.max(0.04, duration2 - 0.05)
-  )
-  const offset = Math.max(0, Number((duration1 - fade).toFixed(3)))
-  const fpsLabel = Number.isInteger(fps) ? String(fps) : fps.toFixed(3)
-  const prepare = `fps=${fpsLabel},scale=${size.width}:${size.height}:flags=bicubic,format=yuv420p,setpts=PTS-STARTPTS`
-  const videoFilter = `[0:v]${prepare}[v0];[1:v]${prepare}[v1];[v0][v1]xfade=transition=fade:duration=${fade.toFixed(3)}:offset=${offset},setpts=PTS-STARTPTS[v]`
-  const encode = [
     '-c:v', 'libx264',
     '-preset', 'fast',
     '-crf', '17',
     '-pix_fmt', 'yuv420p',
     '-movflags', '+faststart'
   ]
+  if (withAudio) args.push('-c:a', 'aac')
+  args.push(outputPath)
+  return args
+}
+
+async function assertStitchLength(part1Path: string, part2Path: string, outputPath: string, fade = 0) {
+  const [duration1, duration2, output] = await Promise.all([
+    probeDuration(part1Path),
+    probeDuration(part2Path),
+    probeDuration(outputPath)
+  ])
+  const expected = duration1 + duration2 - fade
+  if (output < expected * 0.75 || output < duration1 + 0.75) {
+    throw new Error(`Stitched video was ${output.toFixed(2)}s, expected about ${expected.toFixed(2)}s`)
+  }
+}
+
+async function xfadeStitch(part1Path: string, part2Path: string, outputPath: string) {
+  const [duration1, duration2, size, audio1, audio2] = await Promise.all([
+    probeDuration(part1Path),
+    probeDuration(part2Path),
+    probeSize(part1Path),
+    probeHasAudio(part1Path),
+    probeHasAudio(part2Path)
+  ])
+  const fade = Math.min(XFADE_DURATION, Math.max(0.04, duration1 - 0.08), Math.max(0.04, duration2 - 0.08))
+  const offset = Math.max(0, Number((duration1 - fade - 0.04).toFixed(3)))
+  const prepare1 = `scale=${size.width}:${size.height}:flags=bicubic,format=yuv420p,setpts=PTS-STARTPTS`
+  const prepare2 = `select='gte(n,1)',setpts=PTS-STARTPTS,scale=${size.width}:${size.height}:flags=bicubic,format=yuv420p`
+  const videoFilter = `[0:v]${prepare1}[v0];[1:v]${prepare2}[v1];[v0][v1]xfade=transition=fade:duration=${fade.toFixed(3)}:offset=${offset},setpts=PTS-STARTPTS[v]`
+  const runVideo = async (withAudio: boolean) => {
+    const args = [
+      '-y',
+      '-i', part1Path,
+      '-i', part2Path,
+      '-filter_complex', withAudio
+        ? `${videoFilter};[0:a]asetpts=PTS-STARTPTS[a0];[1:a]asetpts=PTS-STARTPTS[a1];[a0][a1]acrossfade=d=${fade.toFixed(3)}:c1=tri:c2=tri[a]`
+        : videoFilter,
+      '-map', '[v]',
+      ...(withAudio ? ['-map', '[a]'] : []),
+      ...encodeArgs(outputPath, withAudio)
+    ]
+    await runFfmpeg(args, 300000)
+  }
+  if (audio1 && audio2) {
+    try {
+      await runVideo(true)
+    } catch {
+      await runVideo(false)
+    }
+  } else {
+    await runVideo(false)
+  }
+  if (!existsSync(outputPath)) {
+    throw new Error('FFmpeg did not write the blended video')
+  }
+  await assertStitchLength(part1Path, part2Path, outputPath, fade)
+}
+
+async function concatReencode(part1Path: string, part2Path: string, outputPath: string) {
+  const audio1 = await probeHasAudio(part1Path)
+  const audio2 = await probeHasAudio(part2Path)
   if (audio1 && audio2) {
     await runFfmpeg([
       '-y',
       '-i', part1Path,
       '-i', part2Path,
-      '-filter_complex', `${videoFilter};[0:a]asetpts=PTS-STARTPTS[a0];[1:a]asetpts=PTS-STARTPTS[a1];[a0][a1]acrossfade=d=${fade.toFixed(3)}:c1=tri:c2=tri[a]`,
+      '-filter_complex', '[0:v]setpts=PTS-STARTPTS[v0];[1:v]select=\'gte(n,1)\',setpts=PTS-STARTPTS[v1];[0:a]asetpts=PTS-STARTPTS[a0];[1:a]asetpts=PTS-STARTPTS[a1];[v0][a0][v1][a1]concat=n=2:v=1:a=1[v][a]',
       '-map', '[v]',
       '-map', '[a]',
-      ...encode,
+      ...encodeArgs(outputPath, true)
-      '-c:a', 'aac',
-      outputPath
     ], 300000)
   } else {
     await runFfmpeg([
       '-y',
       '-i', part1Path,
       '-i', part2Path,
-      '-filter_complex', videoFilter,
+      '-filter_complex', '[0:v]setpts=PTS-STARTPTS[v0];[1:v]select=\'gte(n,1)\',setpts=PTS-STARTPTS[v1];[v0][v1]concat=n=2:v=1:a=0[v]',
       '-map', '[v]',
-      ...encode,
+      ...encodeArgs(outputPath, false)
-      outputPath
     ], 300000)
   }
   if (!existsSync(outputPath)) {
-    throw new Error('FFmpeg did not write the blended video')
+    throw new Error('FFmpeg did not write the stitched video')
   }
+  await assertStitchLength(part1Path, part2Path, outputPath)
 }
 
 export async function concatMp4(part1Path: string, part2Path: string, outputPath: string) {
@@ -223,72 +242,24 @@ export async function concatMp4(part1Path: string, part2Path: string, outputPath
   writeFileSync(listPath, `file '${concatPath(part1Path)}'\nfile '${concatPath(part2Path)}'\n`)
   try {
     await runFfmpeg(['-y', '-f', 'concat', '-safe', '0', '-i', listPath, '-c', 'copy', outputPath], 180000)
-  } catch (copyError) {
+    await assertStitchLength(part1Path, part2Path, outputPath)
-    const audio1 = await probeHasAudio(part1Path)
+  } catch {
-    const audio2 = await probeHasAudio(part2Path)
+    await concatReencode(part1Path, part2Path, outputPath)
-    try {
-      if (audio1 && audio2) {
-        await runFfmpeg([
-          '-y',
-          '-i', part1Path,
-          '-i', part2Path,
-          '-filter_complex', '[0:v][0:a][1:v][1:a]concat=n=2:v=1:a=1[v][a]',
-          '-map', '[v]',
-          '-map', '[a]',
-          '-c:v', 'libx264',
-          '-preset', 'fast',
-          '-crf', '17',
-          '-pix_fmt', 'yuv420p',
-          '-c:a', 'aac',
-          '-movflags', '+faststart',
-          outputPath
-        ], 300000)
-      } else {
-        await runFfmpeg([
-          '-y',
-          '-i', part1Path,
-          '-i', part2Path,
-          '-filter_complex', '[0:v][1:v]concat=n=2:v=1:a=0[v]',
-          '-map', '[v]',
-          '-c:v', 'libx264',
-          '-preset', 'fast',
-          '-crf', '17',
-          '-pix_fmt', 'yuv420p',
-          '-movflags', '+faststart',
-          outputPath
-        ], 300000)
-      }
-    } catch (encodeError) {
-      const copyMessage = copyError instanceof Error ? copyError.message : String(copyError)
-      const encodeMessage = encodeError instanceof Error ? encodeError.message : String(encodeError)
-      throw new Error(`FFmpeg concat failed (${copyMessage}). Re-encode also failed (${encodeMessage}).`)
-    }
-  }
-  if (!existsSync(outputPath)) {
-    throw new Error('FFmpeg did not write the stitched video')
   }
 }
 
 export async function stitchExtension(params: { part1Path: string; part2: Buffer; tmpDir: string }) {
   const part2Path = join(params.tmpDir, 'part2.mp4')
-  const trimmedPath = join(params.tmpDir, 'part2_trim.mp4')
   const finalPath = join(params.tmpDir, 'final_stitched_video.mp4')
   writeFileSync(part2Path, params.part2)
   try {
-    await trimLeadingFrame(part2Path, trimmedPath)
+    await xfadeStitch(params.part1Path, part2Path, finalPath)
-    await xfadeStitch(params.part1Path, trimmedPath, finalPath)
+  } catch (error) {
-  } catch (blendError) {
+    console.error('[stitch] xfade failed, concatenating:', (error as Error).message)
-    try {
+    await concatReencode(params.part1Path, part2Path, finalPath)
-      const trimmedReady = existsSync(trimmedPath)
-      await concatMp4(params.part1Path, trimmedReady ? trimmedPath : part2Path, finalPath)
-    } catch (concatError) {
-      const blendMessage = blendError instanceof Error ? blendError.message : String(blendError)
-      const concatMessage = concatError instanceof Error ? concatError.message : String(concatError)
-      throw new Error(`Seam blend failed (${blendMessage}). Concat fallback also failed (${concatMessage}).`)
-    }
   }
   const stitched = readFileSync(finalPath)
-  for (const extra of [part2Path, trimmedPath, join(params.tmpDir, 'concat_list.txt'), join(params.tmpDir, 'last_frame.png')]) {
+  for (const extra of [part2Path, join(params.tmpDir, 'concat_list.txt'), join(params.tmpDir, 'last_frame.png')]) {
     try { unlinkSync(extra) } catch { /* ignore */ }
   }
   return stitched