39948-vm/backend/src/services/videoProcessing.js

/**
 * Video Processing Service
 *
 * Provides video manipulation operations using FFmpeg.
 * Used for generating reversed videos for back navigation transitions.
 */

const ffmpeg = require('fluent-ffmpeg');
const ffmpegPath = require('ffmpeg-static');
const ffprobePath = require('ffprobe-static').path;
const fs = require('fs').promises;
const path = require('path');
const os = require('os');
const { logger } = require('../utils/logger');

// Configure fluent-ffmpeg to use bundled binaries
ffmpeg.setFfmpegPath(ffmpegPath);
ffmpeg.setFfprobePath(ffprobePath);

let ffmpegQueueTail = Promise.resolve();
let queuedFfmpegJobs = 0;
let ffmpegJobSequence = 0;

function parseFrameRate(value) {
  if (!value) return null;

  if (typeof value === 'number') {
    return Number.isFinite(value) && value > 0 ? value : null;
  }

  const normalized = String(value).trim();
  if (!normalized || normalized === '0/0') return null;

  if (normalized.includes('/')) {
    const [numeratorRaw, denominatorRaw] = normalized.split('/');
    const numerator = Number(numeratorRaw);
    const denominator = Number(denominatorRaw);
    if (!Number.isFinite(numerator) || !Number.isFinite(denominator)) {
      return null;
    }
    if (denominator === 0) return null;
    const fps = numerator / denominator;
    return Number.isFinite(fps) && fps > 0 ? fps : null;
  }

  const parsed = Number(normalized);
  return Number.isFinite(parsed) && parsed > 0 ? parsed : null;
}

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
 * @param {string} filename - Original filename (for extension)
 * @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${ext}`);
  const outputPath = path.join(tempDir, `reversed${ext}`);

  try {
    // Write input buffer to temp file
    await fs.writeFile(inputPath, inputBuffer);

    logger.info({ inputPath, outputPath }, 'Starting video reversal');

    // Reverse video with FFmpeg
    await new Promise((resolve, reject) => {
      ffmpeg(inputPath)
        .outputOptions([
          '-vf',
          'reverse',
          '-af',
          'areverse',
          '-c:v',
          'libx264',
          '-preset',
          'fast',
          '-crf',
          '23',
          '-c:a',
          'aac',
          '-threads',
          '1',
          '-movflags',
          '+faststart',
        ])
        .output(outputPath)
        .on('start', (cmd) => logger.debug({ cmd }, 'FFmpeg command'))
        .on('progress', (progress) => {
          if (progress.percent) {
            logger.debug({ percent: progress.percent }, 'FFmpeg progress');
          }
        })
        .on('end', () => {
          logger.info({ outputPath }, 'Video reversal complete');
          resolve();
        })
        .on('error', (err, stdout, stderr) => {
          logger.error({ err, stdout, stderr }, 'FFmpeg error');
          reject(err);
        })
        .run();
    });

    // Read output as buffer
    return await fs.readFile(outputPath);
  } finally {
    // Cleanup temp files
    try {
      await fs.rm(tempDir, { recursive: true, force: true });
    } catch (cleanupErr) {
      logger.warn({ err: cleanupErr, tempDir }, 'Failed to cleanup temp dir');
    }
  }
}

async function probeMediaMetadata(filePath) {
  return new Promise((resolve, reject) => {
    ffmpeg.ffprobe(filePath, (err, metadata) => {
      if (err) {
        reject(err);
        return;
      }

      const videoStream = metadata?.streams?.find(
        (stream) => stream.codec_type === 'video',
      );
      const audioStream = metadata?.streams?.find(
        (stream) => stream.codec_type === 'audio',
      );
      const primaryStream = videoStream || audioStream || null;
      const formatDuration = Number(metadata?.format?.duration);
      const streamDuration = Number(primaryStream?.duration);
      const durationSec = Number.isFinite(formatDuration) && formatDuration > 0
        ? formatDuration
        : Number.isFinite(streamDuration) && streamDuration > 0
          ? streamDuration
          : null;

      const widthPx = Number(videoStream?.width);
      const heightPx = Number(videoStream?.height);
      const frameRate =
        parseFrameRate(videoStream?.avg_frame_rate) ||
        parseFrameRate(videoStream?.r_frame_rate);

      resolve({
        durationSec,
        widthPx: Number.isFinite(widthPx) && widthPx > 0 ? widthPx : null,
        heightPx: Number.isFinite(heightPx) && heightPx > 0 ? heightPx : null,
        frameRate,
      });
    });
  });
}

/**
 * Check if FFmpeg is available
 * @returns {Promise<boolean>}
 */
async function isFFmpegAvailable() {
  return new Promise((resolve) => {
    ffmpeg.getAvailableFormats((err) => {
      resolve(!err);
    });
  });
}

module.exports = {
  reverseVideo,
  isFFmpegAvailable,
  probeMediaMetadata,
};