feat: try sync audio to video

functions/src/upload.js

@@ -31,11 +31,26 @@ async function downloadToFile(url, destPath) {
 const SCALE_FILTER =
   "scale='trunc(min(1920,iw)/2)*2':'trunc(min(1920,ih)/2)*2':force_original_aspect_ratio=decrease"
 
-async function muxAudioIntoVideo({ videoPath, audioPath, outPath }) {
+async function muxAudioIntoVideo({ videoPath, audioPath, outPath, syncOffset = 0 }) {
   return new Promise((resolve, reject) => {
-    ffmpeg()
-      .input(videoPath) // 0:v
-      .input(audioPath) // 1:a
+    const command = ffmpeg()
+
+    const offset = Number(syncOffset) || 0
+
+    // Si offset > 0 : la vidéo est en avance (ou capturée en retard dans le passé relatif ?), on veut la retarder pour qu'elle commence plus tard
+    // c-à-d on décale le flux vidéo.
+    // Si offset < 0 : on décale l'audio.
+    if (offset > 0) {
+      command.inputOptions(['-itsoffset', String(offset)])
+    }
+    command.input(videoPath) // 0:v
+
+    if (offset < 0) {
+      command.inputOptions(['-itsoffset', String(Math.abs(offset))])
+    }
+    command.input(audioPath) // 1:a
+
+    command
       .outputOptions([
         '-map',
         '0:v:0', // garder la 1re piste vidéo de l'entrée 0
@@ -72,7 +87,7 @@ async function muxAudioIntoVideo({ videoPath, audioPath, outPath }) {
   })
 }
 
-async function uploadPlaybackAsset({ videoUrl, audioUrl, storagePath }) {
+async function uploadPlaybackAsset({ videoUrl, audioUrl, storagePath, syncOffset = 0 }) {
   const tmpDir = await fs.mkdtemp(path.join(os.tmpdir(), 'merge-'))
   const videoPath = path.join(tmpDir, 'video.mp4')
   const audioPath = path.join(tmpDir, 'audio.mp3')
@@ -84,8 +99,8 @@ async function uploadPlaybackAsset({ videoUrl, audioUrl, storagePath }) {
     await downloadToFile(videoUrl, videoPath)
     await downloadToFile(audioUrl, audioPath)
 
-    logger.info('[merge] transcodage/mux ffmpeg')
-    await muxAudioIntoVideo({ videoPath, audioPath, outPath })
+    logger.info('[merge] transcodage/mux ffmpeg', { syncOffset })
+    await muxAudioIntoVideo({ videoPath, audioPath, outPath, syncOffset })
 
     const bucket = admin.storage().bucket()
     const downloadToken = crypto.randomUUID()
@@ -141,7 +156,7 @@ exports.mergeVideoAndAudio = onCall(
     const uid = auth?.uid
     if (!uid) throw new HttpsError('unauthenticated', 'Authentification requise')
 
-    const { videoUrl, audioUrl, storagePath, projectId } = data || {}
+    const { videoUrl, audioUrl, storagePath, projectId, syncOffset } = data || {}
 
     if (!videoUrl || !audioUrl || !storagePath) {
       throw new HttpsError('invalid-argument', 'Requis: { videoUrl, audioUrl, storagePath }')
@@ -152,7 +167,7 @@ exports.mergeVideoAndAudio = onCall(
       throw new HttpsError('permission-denied', `storagePath doit commencer par ${expectedPrefix}`)
     }
 
-    const result = await uploadPlaybackAsset({ videoUrl, audioUrl, storagePath })
+    const result = await uploadPlaybackAsset({ videoUrl, audioUrl, storagePath, syncOffset })
     if (projectId) {
       await markPlaybackCompatibility({ projectId, initiatorUid: uid })
     }