Auto Captions vs Gemini 3.1 TTS: 2026 Guide
Auto captions and Gemini 3.1 Flash TTS both improve videos, but they solve opposite problems. Auto captions turn existing speech into on-screen text, while Gemini 3.1 Flash TTS turns a written script into spoken audio.
TL;DR
Auto Captions takes a video that already has speech and returns a captioned video, which helps with muted, sound-off viewing. Gemini 3.1 Flash TTS takes a text script and generates a spoken voiceover. Use captions when you have footage with dialogue, TTS when you only have a script, and combine them with Lip Sync for talking-head videos. Both are billed in credits, with the cost quoted in the app before you run a job.
Auto captions and Gemini 3.1 Flash TTS both improve videos, but they solve opposite problems. Auto captions pull the words out of existing audio and show them on screen. Gemini 3.1 Flash TTS turns a written script into spoken audio for voiceovers. Flixly offers both, so you can use either on its own or chain them in one workflow.
What Are Auto Captions?
Auto captions transcribe the speech in a video and display it as timed on-screen text, so people can follow along with the sound off. Flixly's Auto Captions tool takes your video and returns a new video with the captions rendered into it.
Key Features of Auto Captions Generators
- Input: a video that already contains speech.
- Output: a captioned video, ready to download and post. It is not a subtitle-file (SRT/VTT) editor.
- Accuracy: depends heavily on audio quality. Clear speech with little background noise gives the best results; heavy music, reverb or overlapping voices cause more mistakes.
- Best for: short social clips, talking heads, tutorials and anything viewed on mute.
Run a test: upload a short talking-head clip, start the job, and check the captioned result. If words are wrong, improve the audio (less background noise, a closer mic) and run it again. The credit cost is quoted before you run it.
Gemini 3.1 TTS Explained
Gemini 3.1 Flash TTS is Google's text-to-speech model, available in Flixly's Text to Speech tool alongside other speech models such as ElevenLabs Multilingual V2, OpenAI TTS and F5-TTS. You can see how it stacks up on our Gemini TTS alternative page. Note that it is a speech model; it is not related to Gemini Omni Flash, which is a video model.
Strengths of Gemini 3.1 TTS
- Natural delivery: modern neural TTS handles pauses and intonation far better than older robotic voices.
- Script-first: you control every word, so it suits explainers, ads and narration where you write the script before recording.
- Multiple languages: useful when you need the same script voiced for different audiences. Check the language list in the app for your target language.
- No recording setup: no microphone, booth or retakes.
Workflow on Flixly: paste your script into Text to Speech, choose Gemini 3.1 Flash TTS and a voice, generate, and listen back. If you want the voice on a visible speaker, take the audio to Lip Sync together with a video of that person. Cost is quoted before you generate.
Head-to-Head Comparison
| Feature | Auto Captions (Flixly) | Gemini 3.1 Flash TTS (via Flixly) |
|---|---|---|
| Primary use | Turn existing speech into on-screen text | Turn a script into speech |
| Input | Video with speech | Text script |
| Output | Captioned video | Audio file |
| Quality depends on | Clarity of the source audio | Script writing and voice choice |
| Cost (Flixly) | Quoted in-app | Quoted in-app |
| Sync | Timed to the speech in the source video | Pair with a video via Lip Sync |
| Best for | Social clips, accessibility, sound-off viewing | Narration, explainers, voiceovers |
Auto captions win when you already have footage with dialogue. Gemini 3.1 Flash TTS wins when you are starting from a script and need a voice.
Use Cases and Real Workflows
Pick based on your goal. Here's how they fit in practice.
Social Media Shorts
Create or edit a short vertical clip, for example in the Video Generator, or use your own footage. Run it through Auto Captions as the final step. Many people scroll feeds with the sound off, so on-screen captions help your message land even when the audio doesn't play.
Professional Narration
Write a short explainer script. Generate the voiceover with Gemini 3.1 Flash TTS in Text to Speech. Create visuals in the Video Generator, then combine the voice with your video in an editor, or use Lip Sync if a presenter should appear to speak the lines. Add polish with Video Effects if the style fits.
Multilingual Dubs
For a video that already has speech, the simplest route is Video Translator, which is built for translating spoken video. If you prefer full control, write or translate the script yourself, voice it with Gemini 3.1 Flash TTS in the target language, sync it with Lip Sync, and caption the finished version with Auto Captions.
Hybrid Workflow: Best of Both
- Record or generate your base video.
- Write or refine the script and voice it with Gemini 3.1 Flash TTS.
- Sync the new audio to your speaker with Lip Sync.
- Run the result through Auto Captions.
- Create a cover image with the Thumbnail Generator.
Each step shows its credit cost before you run it, so you can see the total for the whole pipeline as you go.
Getting Good Results
- Auto Captions: clean audio matters most. Reduce background music and noise before captioning. If your track mixes a song with vocals, Vocal Separation in Music Tools can split the vocals from the backing track.
- Gemini 3.1 Flash TTS: write for the ear. Short sentences, punctuation where you want pauses, and spelled-out numbers or names that could be misread. Listen before you sync it to video.
- Branded voice: if you want your own voice rather than a stock one, Voice Cloning is the tool for that.
Cost and Scalability
Flixly doesn't use monthly tiers. You buy one-time credit packs and spend credits per generation. The cost of a caption job depends on your video, and the cost of a TTS job depends on your script and model; the app quotes both before you run them, so you can compare options for a single video or a large batch of shorts. See current packs on Pricing.
Integration with the Flixly Ecosystem
Flixly lets you chain tools end to end. Build longer cinematic sequences in the Long Video Generator, add a voiceover with Text to Speech, caption the result, and create an animated promo with Motion Poster. Browse the Explore gallery for ideas.
When captions struggle because the original audio is poor, consider replacing the voice track with a Gemini 3.1 Flash TTS voiceover and Lip Sync, then caption the clean version.
Try it: create an account and check the starter credits shown in your dashboard.
Auto captions give you quick accessibility wins on footage you already have. Gemini 3.1 Flash TTS builds polished audio from a script. Start with Auto Captions if you have footage with dialogue, and add TTS when you need a new or translated voice.
Frequently Asked Questions
What is the difference between auto captions and Gemini 3.1 TTS?▾
Auto captions transcribe the speech already in a video and burn it into the picture as captions. Gemini 3.1 Flash TTS generates new speech from a text script. One goes from audio to text, the other from text to audio.
Is Gemini 3.1 TTS better than auto captions for videos?▾
Neither is better; they do different jobs. If you have footage with dialogue, captions make it watchable without sound. If you only have a script, TTS gives you the voiceover. Many videos benefit from both.
What does Flixly Auto Captions produce?▾
Auto Captions returns a new video with the captions rendered into it, ready to post. It is not a subtitle-file editor, so review the result and re-run with cleaner audio if a word comes out wrong.
Can I use Gemini 3.1 TTS for lip sync videos?▾
Yes. Generate the voiceover in Text to Speech, then open Lip Sync and pair that audio with a video of your speaker. The lip sync models need both a video and an audio track. Each step's cost is quoted before you generate.
Can I caption a video after adding a TTS voiceover?▾
Yes. Once your video has the new voice track (for example after Lip Sync), run it through Auto Captions to get a captioned version of the finished clip.
How much does auto captions vs Gemini TTS cost on Flixly?▾
Both are paid with credits, and the app shows the exact cost for your file or script before you run it. Flixly sells one-time credit packs rather than recurring plans, so you only buy credits when you need them.
Which auto captions tool should I use for TikTok and Reels?▾
Flixly Auto Captions works well for short vertical clips because it returns a finished captioned video. Create or edit the clip first, for example in the Video Generator, then caption it as the last step.
