TL;DR — which to pick
Pick AssemblyAI if you need a transcript of your own audio or video. ReelsBuilder's standalone transcription and caption-rendering endpoints are not available yet.
Pick ReelsBuilder if what you actually want is a finished short-form video with burned-in captions — generated from a prompt, an article, or a YouTube source — rather than the transcript itself.
Philosophical difference
AssemblyAI is a specialized audio intelligence company. The transcript is their deliverable, and they invest deeply in accuracy and downstream audio analysis.
ReelsBuilder is a short-form video pipeline. Transcription happens inside our renders so we can time captions to the narration, but it is not exposed as its own API today.
Feature comparison
| Capability | AssemblyAI | ReelsBuilder |
|---|---|---|
| Transcribe your own audio/video via API | ✅ | ❌ Not available yet |
| Speaker diarization | ✅ Mature, configurable | ❌ |
| Auto-chapters, sentiment, entities, summarization | ✅ | ❌ |
| PII redaction, content moderation | ✅ | ❌ |
| Realtime / streaming STT | ✅ | ❌ |
| Caption file export (SRT/VTT) | ⚠️ Format yourself | ❌ |
| Captions burned into generated videos | ❌ | ✅ On by default for ReelsBuilder renders and clips |
| Captioning a video you upload | ❌ | ❌ Not available yet |
| Bundled with video generation | ❌ | ✅ |
Pricing
There is no ReelsBuilder transcription price because there is no transcription endpoint. Captions are included in the price of a render (for example $0.50 for Magic Video or $0.60 for /generate-and-post on live API keys).
Where AssemblyAI wins
- It exists for your audio. Transcribe any file you have. We can't today.
- Audio intelligence features. Sentiment, entity detection, auto-chapters, summarization, content moderation.
- Realtime streaming. Live transcription via WebSocket.
Where ReelsBuilder wins
- Finished captioned video. If the transcript was only ever a means to a captioned short, a ReelsBuilder render gives you the end product directly.
- Bundled pipeline. Script, voice, captions, render and (optionally) posting on one API key.
When to use both
Use AssemblyAI for transcripts of your own recordings. If you then want a short-form video about that content, send the text you care about as the script or article text to /generate-and-post or /blog-to-video. ReelsBuilder does not accept external transcript files as caption input.