Costs2 min read
What speech to text really costs for NotebookLM captions
Captioning a NotebookLM overview is cheaper than most people assume, because the thing you send is not the video. This page explains what actually crosses the network, what the free tiers allow, and when a paid key becomes worth it.
You send audio, not video
A ten minute Video Overview is roughly 50 MB as an MP4. LM Subs reads the audio track out of the stream in your browser and sends that instead, which for the same overview is around 3 MB. Smaller uploads mean faster responses, fewer rejected requests, and a much lower chance of hitting a provider's payload cap.
Free tiers that cover normal use
| Provider | Free plan | Good to know |
|---|---|---|
| Groq | Permanent free plan, no card | Generous daily audio allowance, so most people never pay |
| Mistral | Free Experiment plan | No card, needs a phone verification step |
| Local Whisper | Unlimited | Runs on your machine, no provider involved at all |
When paying starts to make sense
- You caption more than a handful of long Audio Overviews every day.
- You need word level timestamps for a language the free models handle poorly.
- You are captioning for a team and do not want to share one free key.
- You want a larger model than the free tier exposes.
Paid speech to text is billed per minute of audio, and the per minute prices are low enough that a long overview costs a fraction of a cent on most providers. The real cost driver is volume, not the individual video.
How to keep the bill at zero
- Order the queue by costPut Groq first, Mistral second, and a local server last. Failover moves down the list only when a provider refuses the request.
- Store one key per providerTwo configured providers beat one, because a rate limit on the first no longer stops your work.
- Reuse the transcriptLM Subs caches generated captions per media item, so replaying an overview does not pay for it twice.
- Caption what you needAuto generation is a switch. Turn it off if you only need captions occasionally.
Frequently asked questions
Is LM Subs itself free?
Yes. The extension is free and MIT licensed. You pay only if you choose a provider that charges, and the recommended starting providers both have permanent free tiers.
What happens when a free key runs out of quota?
The provider returns a rate limit response, LM Subs marks that provider as unavailable for the request, and the next provider in your queue takes over automatically.
Does an Audio Overview cost more than a Video Overview?
Billing is per minute of audio, so a twenty minute podcast costs more than a three minute video simply because it is longer. There is no separate charge for the Audio Overview format.