Transcoding Videos from Google Cloud Storage using FFMPEG in Google Cloud Functions

02 Nov 2017


The meat of this is from a comment on this blog post but I wanted to write a dedicated post about it because the blog post ends with an “impossible” conclusion but that isn’t the case, if you are using GCS triggers and not multipart uploads. Hats off to sjurgis for the code!


GCS - Google Cloud Storage GCF - Google Cloud Function


When a video is uploaded to a certain GCS bucket, transcode the video and place it in another GCS bucket.

For my particular use case, I wanted to transcode video recorded by the Media Recorder API, from WebM with H264/Opus to MP4 with H264/AAC. The idea being that MP4 with H264/AAC would be universally playable because ahem, Apple.


You’ll need the following APIs activated on Google Cloud: Storage, Cloud Functions.

You’ll need to create two GCS buckets. One for user uploads, one for the final transcoded videos.

Your cloud function will have the following dependencies:

The Code

This will live on a GCF that is triggered by the upload GCS bucket.

const storage = require('@google-cloud/storage')();
const ffmpegPath = require('@ffmpeg-installer/ffmpeg').path;
const ffmpeg = require('fluent-ffmpeg');

const transcodedBucket = storage.bucket('transcode');
const uploadBucket = storage.bucket('upload');

exports.transcodeVideo = function transcodeVideo(event, callback) {
  const file = event.data;

  // Ensure that you only proceed if the file is newly created, and exists.
  if (file.metageneration !== '1' || file.resourceState !== 'exists') {

  // Open write stream to new bucket, modify the filename as needed.
  const remoteWriteStream = transcodedBucket.file(file.name.replace('.webm', '.mp4'))
      metadata: {
        metadata: file.metadata, // You may not need this, my uploads have associated metadata
        contentType: 'video/mp4', // This could be whatever else you are transcoding to

  // Open read stream to our uploaded file
  const remoteReadStream = uploadBucket.file(file.name).createReadStream();

  // Transcode
    .outputOptions('-c:v copy') // Change these options to whatever suits your needs
    .outputOptions('-c:a aac')
    .outputOptions('-b:a 160k')
    .outputOptions('-f mp4')
    .outputOptions('-preset fast')
    .outputOptions('-movflags frag_keyframe+empty_moov')
    // https://github.com/fluent-ffmpeg/node-fluent-ffmpeg/issues/346#issuecomment-67299526 
    .on('start', (cmdLine) => {
      console.log('Started ffmpeg with command:', cmdLine);
    .on('end', () => {
      console.log('Successfully re-encoded video.');
    .on('error', (err, stdout, stderr) => {
      console.error('An error occured during encoding', err.message);
      console.error('stdout:', stdout);
      console.error('stderr:', stderr);
    .pipe(remoteWriteStream, { end: true }); // end: true, emit end event when readable stream ends

And yea, that’s all! I’ve only tested it on a handful of videos so far but it seems to work nicely. You can have another GCF listening to the final transcoded bucket in case you need to do something else with the transcoded file. It’s all pretty intuitive.


Transcoding videos in GCF with FFMPEG is totally possible if the files are streamed from GCS. Just be careful of invoking overly long GCF processing times, it could be expensive. This setup makes for a flexible on-demand transcoding flow if you have a low volume side project and don’t want to pay for dedicated servers to sit idle.