100% on your device, No upload, No sign-up
Subtitles, done by AI in your browser
Generate, translate, sync, edit, burn in and dub subtitles. Every AI model runs on your device, so your videos never leave it.
28 tools, 15 formats, 33 languages
Popular tools
- AI toolsAI Subtitle GeneratorGenerate timed subtitles from any video or audio with Whisper AI, running privately in your browser.
- AI toolsFree TikTok CaptionsAuto-generate animated word-by-word captions for TikTok, Reels and Shorts, then burn them into your video. Free, no watermark, no upload: the AI runs in your browser.
- AI toolsSubtitle TranslatorTranslate SRT, VTT, ASS and other subtitles into 30+ languages with AI models that run in your browser. Nothing is uploaded.
- AI toolsVideo Translator (AI Dubbing)Transcribe a video, translate it and dub it with an AI voice, or burn in translated subtitles. All in one place.
- AI toolsAuto Sync Subtitles (AI)Fix out-of-sync subtitles automatically: AI listens to the video and lines the subtitles up with the speech.
- AI toolsText to Speech (AI Voice)Turn any text into natural speech with AI voices that run in your browser. Download MP3 or WAV.
- AI toolsRemove Background NoiseRemove fan hum, traffic, wind and keyboard noise from voice recordings and videos with free AI that runs in your browser. No upload, no watermark.
- AI toolsVocal Remover (Karaoke)Separate the vocals from the music of any song or video with free AI that runs in your browser: get a karaoke instrumental and an a cappella track. No upload, no sign-up.
- EditOnline Subtitle EditorEdit subtitles with a video preview and waveform: drag timings, split, merge, find and replace, undo.
- EditAdd Subtitles to Video (Burn-in)Burn subtitles permanently into your video with classic, boxed or TikTok-style word-by-word captions. Rendered in your browser.
- EditShift SubtitlesMove every subtitle earlier or later by a fixed amount of time.
- ConvertUniversal Subtitle ConverterConvert subtitles between SRT, VTT, ASS, SBV, SUB, SMI, TTML, LRC, TXT, CSV, JSON, Word and PDF.
- ConvertExtract Subtitles from VideoPull embedded subtitle tracks out of MKV, MP4 and MOV files and save them as SRT or any other format. Image subtitles are read with OCR.
Why FastSub AI
Private by design
Files are processed on your device. Nothing is uploaded, logged or stored on a server.
Real AI, no cloud
Whisper speech recognition, translation, OCR and voices run in the browser with WebGPU or WebAssembly.
Free, no limits
No account, no watermark, no per-minute pricing. Long videos cost the same as short ones.
Pro-grade output
Netflix-style quality checks, word-level timing, 15+ formats including ASS, TTML, FCPXML and Word.
AI tools
- AI Subtitle GeneratorGenerate timed subtitles from any video or audio with Whisper AI, running privately in your browser.
- Free TikTok CaptionsAuto-generate animated word-by-word captions for TikTok, Reels and Shorts, then burn them into your video. Free, no watermark, no upload: the AI runs in your browser.
- Subtitle TranslatorTranslate SRT, VTT, ASS and other subtitles into 30+ languages with AI models that run in your browser. Nothing is uploaded.
- Video Translator (AI Dubbing)Transcribe a video, translate it and dub it with an AI voice, or burn in translated subtitles. All in one place.
- Auto Sync Subtitles (AI)Fix out-of-sync subtitles automatically: AI listens to the video and lines the subtitles up with the speech.
- Text to Speech (AI Voice)Turn any text into natural speech with AI voices that run in your browser. Download MP3 or WAV.
- Remove Background NoiseRemove fan hum, traffic, wind and keyboard noise from voice recordings and videos with free AI that runs in your browser. No upload, no watermark.
- Vocal Remover (Karaoke)Separate the vocals from the music of any song or video with free AI that runs in your browser: get a karaoke instrumental and an a cappella track. No upload, no sign-up.
- Interview Transcription with SpeakersTranscribe interviews and meetings and label who is speaking, with AI speaker detection that runs in your browser.
- Subtitles to Speech (AI Voiceover)Turn SRT or VTT subtitles into a timed AI voice track, or dub a video with it. Runs in your browser.
- PGS to SRT (OCR)Turn Blu-ray PGS image subtitles (.sup or inside MKV) into editable SRT text with OCR, in your browser.
Edit
- Online Subtitle EditorEdit subtitles with a video preview and waveform: drag timings, split, merge, find and replace, undo.
- Add Subtitles to Video (Burn-in)Burn subtitles permanently into your video with classic, boxed or TikTok-style word-by-word captions. Rendered in your browser.
- LRC Lyrics EditorSync lyrics to a song by tapping along, fine-tune each line and export LRC or SRT.
- Shift SubtitlesMove every subtitle earlier or later by a fixed amount of time.
- Resync SubtitlesFix drifting subtitles with two sync points: set where the first and last lines should start.
- Subtitle FPS ConverterFix subtitles that drift because they were made for a different frame rate (23.976, 25, 29.97…).
- Subtitle Speed AdjustmentRetime subtitles for a video played faster or slower, like 1.25× or 2×.
- Merge SubtitlesCombine subtitle files: overlay two languages, or join CD1 and CD2 into one file.
- Dual Subtitles (Bilingual)Combine two subtitle files in different languages into one bilingual file: two lines per subtitle, or one language on top and one at the bottom. Great for learning languages.
- Split SubtitlesCut a subtitle file at a timestamp or into equal parts.
- Remove SDH / Hearing-Impaired TagsStrip [music], (laughs), speaker names and other hearing-impaired annotations from subtitles in one click.
- Subtitle Encoding Fixer (UTF-8)Fix garbled characters by detecting the encoding (Windows-1252, GBK, Shift-JIS…) and saving as UTF-8.
- Subtitle Quality CheckerFind lines that are too fast to read, too long, overlapping or flashing by, using Netflix-style rules.
Convert
- Universal Subtitle ConverterConvert subtitles between SRT, VTT, ASS, SBV, SUB, SMI, TTML, LRC, TXT, CSV, JSON, Word and PDF.
- Extract Subtitles from VideoPull embedded subtitle tracks out of MKV, MP4 and MOV files and save them as SRT or any other format. Image subtitles are read with OCR.
- CapCut to SRT ConverterConvert CapCut project (CapCut) subtitles to SubRip (SRT) for free, right in your browser. No upload, no sign-up.
- Text to SRTTurn plain text into timed subtitles. Each line becomes a cue, timed by reading speed.
Format converters
- Convert Subtitles to SRT
- Convert Subtitles to VTT
- Convert Subtitles to ASS
- Convert Subtitles to SBV
- Convert Subtitles to SUB
- Convert Subtitles to SMI
- Convert Subtitles to TTML
- Convert Subtitles to LRC
- Convert Subtitles to TXT
- Convert Subtitles to CSV
- Convert Subtitles to JSON
- SRT VTT
- SRT ASS
- SRT SBV
- SRT SUB
- SRT SMI
- SRT TTML
- SRT LRC
- SRT FCPXML
- SRT TXT
- SRT CSV
- SRT JSON
- SRT Word
- SRT PDF
- VTT SRT
- VTT ASS
- VTT SBV
- VTT SUB
- VTT SMI
- VTT TTML
- VTT LRC
- VTT FCPXML
- VTT TXT
- VTT CSV
- VTT JSON
- VTT Word
- VTT PDF
- ASS SRT
- ASS VTT
- ASS SBV
- ASS SUB
- ASS SMI
- ASS TTML
- ASS LRC
- ASS FCPXML
- ASS TXT
- ASS CSV
- ASS JSON
- ASS Word
- ASS PDF
- SBV SRT
- SBV VTT
- SBV ASS
- SBV SUB
- SBV SMI
- SBV TTML
- SBV LRC
- SBV FCPXML
- SBV TXT
- SBV CSV
- SBV JSON
- SBV Word
- SBV PDF
- SUB SRT
- SUB VTT
- SUB ASS
- SUB SBV
- SUB SMI
- SUB TTML
- SUB LRC
- SUB FCPXML
- SUB TXT
- SUB CSV
- SUB JSON
- SUB Word
- SUB PDF
- SMI SRT
- SMI VTT
- SMI ASS
- SMI SBV
- SMI SUB
- SMI TTML
- SMI LRC
- SMI FCPXML
- SMI TXT
- SMI CSV
- SMI JSON
- SMI Word
- SMI PDF
- TTML SRT
- TTML VTT
- TTML ASS
- TTML SBV
- TTML SUB
- TTML SMI
- TTML LRC
- TTML FCPXML
- TTML TXT
- TTML CSV
- TTML JSON
- TTML Word
- TTML PDF
- LRC SRT
- LRC VTT
- LRC ASS
- LRC SBV
- LRC SUB
- LRC SMI
- LRC TTML
- LRC FCPXML
- LRC TXT
- LRC CSV
- LRC JSON
- LRC Word
- LRC PDF
- CapCut VTT
- CapCut ASS
- CapCut SBV
- CapCut SUB
- CapCut SMI
- CapCut TTML
- CapCut LRC
- CapCut FCPXML
- CapCut TXT
- CapCut CSV
- CapCut JSON
- CapCut Word
- CapCut PDF
Frequently asked questions
Is FastSub AI free?
Yes. Every tool on FastSub AI is free, with no sign-up, no watermark and no usage limits.
Are my files uploaded anywhere?
No. Your files are read and processed inside your browser tab. The only downloads are the app itself and, for AI tools, the model files.
Why does the first run download a model?
The AI runs on your own device, so the model has to be on it. It downloads once and your browser keeps it cached, so later runs start straight away and even work offline.
Which browsers work best?
Any modern browser works. AI tools are fastest in Chrome or Edge on a desktop with WebGPU; other browsers fall back to the CPU, which is slower but works.
Which subtitle formats are supported?
SRT, WebVTT, ASS/SSA, SBV, SUB (MicroDVD), SAMI, TTML/DFXP, LRC and CapCut projects in; all of those plus TXT, CSV, JSON, FCPXML, Word and PDF out.