limited ffmpeg reverse video generation

backend/src/services/videoProcessing.js

@@ -17,6 +17,43 @@ const { logger } = require('../utils/logger');
 ffmpeg.setFfmpegPath(ffmpegPath);
 ffmpeg.setFfprobePath(ffprobePath);
 
+let ffmpegQueueTail = Promise.resolve();
+let queuedFfmpegJobs = 0;
+let ffmpegJobSequence = 0;
+
+async function enqueueFfmpegJob(jobName, runJob) {
+  const jobId = ++ffmpegJobSequence;
+  const queuedAhead = queuedFfmpegJobs;
+
+  queuedFfmpegJobs++;
+
+  logger.info(
+    { jobId, jobName, queuedAhead },
+    'FFmpeg job queued for single-worker execution',
+  );
+
+  const previousTail = ffmpegQueueTail.catch(() => {
+    // Keep the queue moving even if the previous job failed.
+  });
+
+  const jobPromise = previousTail.then(async () => {
+    queuedFfmpegJobs = Math.max(0, queuedFfmpegJobs - 1);
+    logger.info(
+      { jobId, jobName, queuedRemaining: queuedFfmpegJobs },
+      'FFmpeg job started',
+    );
+
+    try {
+      return await runJob();
+    } finally {
+      logger.info({ jobId, jobName }, 'FFmpeg job finished');
+    }
+  });
+
+  ffmpegQueueTail = jobPromise;
+  return jobPromise;
+}
+
 /**
  * Reverse a video using FFmpeg
  * @param {Buffer} inputBuffer - Input video buffer
@@ -24,6 +61,12 @@ ffmpeg.setFfprobePath(ffprobePath);
  * @returns {Promise<Buffer>} Reversed video buffer
  */
 async function reverseVideo(inputBuffer, filename) {
+  return enqueueFfmpegJob('reverseVideo', () =>
+    reverseVideoWithoutQueue(inputBuffer, filename),
+  );
+}
+
+async function reverseVideoWithoutQueue(inputBuffer, filename) {
   const tempDir = await fs.mkdtemp(path.join(os.tmpdir(), 'video-reverse-'));
   const ext = path.extname(filename) || '.mp4';
   const inputPath = path.join(tempDir, `input${ext}`);
@@ -51,6 +94,8 @@ async function reverseVideo(inputBuffer, filename) {
           '23',
           '-c:a',
           'aac',
+          '-threads',
+          '1',
           '-movflags',
           '+faststart',
         ])