Transcribing short voice memos is straightforward. But when you need to transcribe long audio files—such as a 2-hour board meeting, a detailed user research session, or a long-form podcast prep call—you will quickly run into limitations.
Most AI transcription APIs (like OpenAI's Whisper) have strict file size limits (e.g., 25MB). Trying to upload a 300MB audio file will result in timeouts or API errors.
This guide explains how to transcribe long audio files on macOS, comparing manual workarounds with justREC's automated workflow.
The Core Challenge: Why Long Audio Fails
When you send audio to an AI model, the process can fail for three reasons:
- API File Limits: OpenAI's Whisper API restricts uploads to 25MB. High-quality uncompressed audio (like WAV or AIFF) hits this limit in less than 15 minutes.
- Network Interruptions: If your Wi-Fi drops for a few seconds during a 100MB file upload, the transfer fails, forcing you to restart from scratch.
- Memory Limits: Running local heavy Whisper models on basic laptop hardware can cause system slowdowns or application crashes.
Option 1: The Manual Workaround
If you want to transcribe a long audio file manually:
- Compress the Audio: Convert your WAV file to MP3 or M4A (AAC) using tools like FFmpeg or Audacity to reduce the file size.
- Split the File: If the file is still larger than 25MB, you must slice the audio into smaller chunks (e.g., 20-minute parts).
- Upload Separately: Upload each chunk to the transcription API.
- Merge the Transcripts: Download the individual text outputs and stitch them back together manually in a text editor, ensuring timestamps remain aligned.
Option 2: The justREC Automated Way
justREC handles this entire process automatically on your Mac:
1. Size-Based Chunking
When you record a meeting or import an external audio file, justREC automatically splits the audio into smaller, optimized parts based on the file size.
2. Part-by-Part Upload
The app uploads the chunks sequentially. If you are transcribing a 2-hour call, it uploads part 1, waits for the transcript, then uploads part 2. This keeps network requests small and reliable.
3. Autosave Manifest
justREC writes a temporary manifest file locally on your Mac's drive. If your internet connection drops in the middle of part 8 of 12, the progress is saved. When the connection is restored, you simply click Resume and the app continues where it left off, rather than transcribing the first 7 parts again.
4. Direct Export
Once all parts are processed, justREC stitches the transcripts together, runs your custom summary templates, and exports a single, clean Markdown or DOCX file to your local workspace.
How to Get Started
Avoid slicing audio files manually. Install justREC on your Mac, import your long audio file (supported on the Lifetime unlock), and let the app handle the chunking, transcription, and summarization automatically.