cloudformation-webm-mp3 is an AWS SAM + CloudFormation template designed to ingest WEBM audio files and convert them to MP3 files. It sends a notification through SNS to keep track of progress, generate information about the audio file (like duration) 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 audio inputs. This bucket MUST NOT already exist.
OutputBucketName	Yes		The name of the bucket to use for output audio files. 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-audio	The name of the Fargate container.

Outputs

Output	Description
InputBucket	The name of the bucket where audio files should be uploaded.
InputBucketArn	The ARN for the bucket where audio files 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-mp3/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-audio

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-mp3/VERSION/template.yaml

becomes this:

https://sammarks-cf-templates-us-east-2.s3.amazonaws.com/webm-mp3/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 audio 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 an audio file needs to be converted.

How does it work?

Whenever an audio file is uploaded to the input bucket, it goes through the following process:

• The Lambda is triggered and verifies the file 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 file to temporary storage, runs it through ffmpeg to convert the container from WEBM to MP3, and then uploads the result to the destination bucket inside S3.
  • It gathers information about the audio file (like duration) and records it as well.
• Send a notification to SNS when the process is complete or errors.

Why Fargate / Docker containers?

See cloudformation-webm-mp4 for more information.

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-mp3/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 audio files to mp3 files.
• 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?

The inspiration for this template was to easily convert audio files generated using the MediaRecorder APIs to MP3 files 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 converting audio files is quick and easy with the smaller file sizes, so we don't need the massive amount of CPU power something like AWS' ElementalMedia provides.