Assembly Webhook lambda

[cjjenkinson]

Assembly.ai will asynchronously dispatch webhook events which we will subscribe to that will tell us the current state of the transcribe job.

Add the infrastructure to expose a HTTP api gateway endpoint that triggers a lambda function responsible for handling a completed or failed transcription job.

• Create CDK resources to expose /webhook that triggers assembly webhook lambda
• Update Assembly.AI calls to include generated API gateway endpoint so events can be returned to it

Lambda logic

• Upon receiving async events from Assembly.AI determine the success or failure of the job
• If failed mark video state as failed
• If success then fetch the transcription output SRT file from Assembly.AI and store in S3 transcriptions bucket prefixed with the video ID for easy look up
• Update the video to hold the transcriptionKey so it can be looked up by the encoding lambda when it will use the subtitles to encode onto a video