cloudformation-webm-mp4: A JavaScript repository from sammarks

cloudformation-webm-mp4 is an AWS SAM + CloudFormation template designed to ingest WEBM videos encoded with the H264 Codec (possible using MediaRecorder APIs), and convert them to MP4 videos with the same H264 video codec. It sends a notification through SNS to keep track of progress and completion.

Get Started

It's simple! Click this fancy button:

Then give the stack a name, and configure it:

Parameters

Parameter	Required	Default Value	Description
InputBucketName	Yes		The name of the bucket to use for video inputs. This bucket MUST NOT already exist.
OutputBucketName	Yes		The name of the bucket to use for output videos. This bucket MUST already exist.
SubnetNames	Yes		A comma-separated list of VPC subnets to launch the Fargate container in.
SecurityGroupNames	Yes		A comma-separated list of VPC security groups (that have access to the internet) to launch the Fargate container in.
ContainerName	No	`webm-convert`	The name of the Fargate container.

Outputs

Output	Description
InputBucket	The name of the bucket where videos should be uploaded.
InputBucketArn	The ARN for the bucket where videos should be uploaded.
Topic	The ARN for the SNS Topic to subscribe to for pipeline notifications.
S3Topic	The ARN for the SNS Topic to subscribe to for object creation notifications from the input bucket.

Usage in Another Stack or Serverless

Add something like this underneath resources:

videoThumbnailStack:
  Type: AWS::CloudFormation::Stack
  Properties:
    TemplateURL: https://sammarks-cf-templates.s3.amazonaws.com/webm-mp4/VERSION/template.yaml
    Parameters:
      InputBucketName: test-input-bucket
      OutputBucketName: test-output-bucket
      SubnetNames: subnet-aaaaa,subnet-bbbbb
      SecurityGroupNames: sg-aaaaa,sg-bbbbb
      ContainerName: webm-convert

Note: This stack will require the CAPABILITY_AUTO_EXPAND capability when deploying the parent stack with CloudFormation. If you are using the Serverless framework, you can "trick" it into adding the required capabilities by adding this to your serverless.yaml:

resources:
  Transform: 'AWS::Serverless-2016-10-31' # Trigger Serverless to add CAPABILITY_AUTO_EXPAND
  Resources:
    otherResource: # ... all of your original resources

Regions

A quick note on regions: If you are deploying this stack in a region other than us-east-1, you need to reference the proper region S3 bucket as we're deploying Lambda functions. Just add the region suffix to the template URL, so this:

https://sammarks-cf-templates.s3.amazonaws.com/webm-mp4/VERSION/template.yaml

becomes this:

https://sammarks-cf-templates-us-east-2.s3.amazonaws.com/webm-mp4/VERSION/template.yaml

Subscribing to object creation events

S3 does not allow two separate Lambda functions to be subscribed to the same event types on a single bucket. Because of this, the template creates an SNS topic to serve as the messenger for the S3 notifications, and the internal Lambda function subscribes to that SNS topic.

Because of this, if you want to subscribe to the object creation events in your own Lambda functions, simply create a Lambda function that references the S3Topic output of this stack.

What's deployed?

One S3 bucket, for video input.
A SNS topic for notifications.
A SNS topic for object created notifications for the input bucket.
An ECS cluster and task definition to contain the configuration for the conversion Docker container.
A Lambda function to launch a new instance of the task definition inside Fargate when a video needs to be converted.

How does it work?

Whenever a video is uploaded to the input bucket, it goes through the following process:

The Lambda is triggered and verifies the video ends in .webm - it will throw an error if it does not.
Lambda creates a new instance of the task definition and launches it inside Fargate with your provided VPC configuration.
The Docker container downloads the video to temporary storage, runs it through ffmpeg to convert the container from WEBM to MP4, and then uploads the result to the destination bucket inside S3.
Send a notification to SNS when the process is complete or errors.

Why Fargate / Docker containers?

In the initial version of this project, we were just running the conversion inside a Lambda function with ffmpeg included in the deployment package. We would stream the video file from S3 directly into an ffmpeg process, and then stream the results back up to S3 all while doing the conversion.

The problem with this is we weren't able to generate the moov atom that MP4 requires and uses to encode information like the duration of the video, so we had to pass flags to tell ffmpeg to not create the moov atom. Ffmpeg requires seekable output in order to generate the moov atom, and we can't seek to different parts of the file if we're uploading a stream to S3.

The solution is to download the entire file, store it in temporary storage, then run the entire file through ffmpeg, and then upload the result to S3, all separately. Unfortunately, Lambda is limited to 512MB of temporary storage, and that temporary storage is shared across invocations of a function. This means if you don't clean up the files in /tmp appropriately across invocations, you will quickly run out of space.

This effectively meant that the filesize of our videos would be limited to, at a maximum, 256MB. It would be possible for a video to exceed that size, and we need this solution to work 100% of the time. Therefore, the next best thing is to create a Docker container and run it inside AWS Fargate so we don't have to manage a cluster of Docker containers and only pay for the hours of the machine that we use. Would Fargate not have existed, the next best solution would probably be to just launch an EC2 instance whenever we wanted to do the conversion, and then shut it down when we're done.

Accessing Previous Versions & Upgrading

Each time a release is made in this repository, the corresponding template is available at:

https://sammarks-cf-templates.s3.amazonaws.com/webm-mp4/VERSION/template.yaml

On upgrading: I actually recommend you lock the template you use to a specific version. Then, if you want to update to a new version, all you have to change in your CloudFormation template is the version and AWS will automatically delete the old stack and re-create the new one for you.

Features

Automatically convert webm videos encoded in the H264 codec to mp4 videos with the same codec.
Send notifications about updates and error messages to a SNS topic.
Uses AWS Lambda + AWS Fargate so you only pay for the hours you are actively converting something.
Deploy with other CloudFormation-compatible frameworks (like the Serverless framework).
All functionality is self-contained within one CloudFormation template. Delete the template, and all of our created resources are removed.

Why use this?

As I mentioned briefly above, the inspiration for this template was to easily convert videos generated using the MediaRecorder APIs (which support H264 in WEBM format), to MP4 videos for broader consumption on mobile devices.

Running a Docker container with ffmpeg installed inside AWS Fargate to achieve this becomes immensely cheaper than using something like AWS' ElementalMedia services because we're just doing a simple container change instead of re-encoding the video into a different codec, so we don't need the massive amount of CPU power something like AWS' ElementalMedia provides.

sammarks/cloudformation-webm-mp4