Building a Podcast-to-Newsletter Pipeline with n8n, OpenAI, and Postmark

I built an n8n workflow that automatically converts podcast audio files into formatted newsletters and distributes them via email. Here's how I architected the integration between Google Drive, OpenAI's APIs, and Postmark. Architecture Overview The workflow follows this data flow: Audio Source : Monitor Google Drive folder for new audio files Transcription : Send audio to OpenAI Whisper API for speech-to-text Content Generation : Pass transcript to GPT-4.1-mini for newsletter creation Distribution : Retrieve subscriber list from Google Sheets and send via Postmark I chose this architecture because it separates concerns cleanly—Google Drive handles storage, OpenAI handles AI processing, and Postmark handles reliable email delivery. Each service does what it does best. [Google Drive] → [Download Audio] → [Whisper API] → [GPT-4.1-mini] → [Postmark API] ↑ [Google Sheets] API Integration Deep-Dive OpenAI Whisper Transcription Authentication : API key from OpenAI dashboard Request format : P