Bilingual subtitle tool for video localizationOne product video, finished in 20 languages
Upload a video or audio, transcribe the speech automatically, translate into 20 languages, and burn bilingual subtitles into a video you can publish as-is
The same product video, and where it differs
When buyers in your target market cannot follow the Chinese voice-over, the subtitles are the only basis on which they decide whether to keep watching
Original with Chinese voice-over only
- Overseas buyers do not understand it and swipe away in the first 3 seconds
- Scrolling the feed on mute, they have no idea what is being said
- A low completion rate drives ad cost up
Finished with bilingual subtitles
- Original and translation on screen together — understandable and verifiable
- Watchable on mute, with completion and click-through rates rising together
- One clip, a new subtitle set, and it can run in several markets
Make it once, fit the main ad placements
Subtitles are laid out automatically to the aspect ratio, so you do not re-edit for each platform
16:9 landscape
YouTube, your own site, Amazon product videos
9:16 vertical
TikTok, Reels, Shorts, Kuaishou
1:1 square
Feed ads, product hero videos
Your product video will not sit on our servers long-term
- · The uploaded video and the extracted audio are cleared from disk once processing finishes or the session ends, and are not used for any other purpose;
- · A disk watermark guard pauses new uploads once a threshold is crossed, so leftovers cannot pile up;
- · To support billing and reconciliation, task records, credit ledgers and other metadata are kept — this does not include your video or audio files.
Note: this page describes only what we actually do. The full retention scope and time limits are in the About and privacy notes.
Upload a video file
An AI speech recognition engine generates the subtitles accurately
Drag a video or audio file here, or click to choose
Video MP4, AVI, MOV, MKV, WMV, FLV ｜ Audio MP3, WAV, M4A, FLAC, OGG, AAC
✨ The video is decoded in the browser and only the audio is uploaded; audio files are uploaded directly. Safe and reliable
Paste an online video URL
No download, no upload — watch while bilingual subtitles are generated
- Supports direct mp4 / m3u8
- Web page URLs that contain a video are supported too
- Live subtitles — toggle the original and the translation at any time
💡 Credit calculator
Who uses SmileSub to go global
One feature set, three typical scenarios
Cross-border e-commerce sellers
Product and review videos get subtitles in the target market language and go straight to TikTok, your own store or Amazon.
Creators going global
Chinese voice-overs on YouTube / TikTok get foreign-language subtitles automatically, putting the content in front of non-Chinese-speaking viewers.
Foreign trade promo videos
Alibaba.com listings, trade shows and product intro videos become bilingual so overseas clients can follow them directly.
Why choose SmileSub?
Advanced AI gives you a professional-grade subtitle workflow
Privacy and security
Server-side AI processing, with secure transfer and storage
Fast generation
Efficient concurrent processing completes subtitle generation quickly
Multiple languages
Recognition covers Chinese, English, Japanese and Korean; translation covers 20 languages
High-accuracy engine
A cloud speech recognition engine with high accuracy on Chinese voice-overs, steady even in noisy conditions
What sellers use it for
Product explainer videos
Factory footage and feature demos in the target market language, so buyers follow the selling points
Feed ad creative
Understandable on mute, lifting completion and click-through rates while ad cost comes down
Batch new product videos
A batch of SKU videos gets subtitles and translations in one go, with no line-by-line manual work
Three simple steps to generate subtitles
Upload a video
MP4, AVI, MOV and other common formats — just drag and drop
AI recognition
AI extracts the audio and produces accurate subtitle text automatically
Download subtitles
SRT, VTT and more, ready to use in video editing
Advanced AI technology
The technology behind SmileSub
Cloud speech recognition engine
It connects to a mature cloud speech recognition service, tuned in practice for voice-over material in Chinese, English, Japanese and Korean. It suits clear human speech such as product explainers and e-commerce voice-overs. Recognition runs in the cloud, so your computer carries no compute load and is not limited by its own performance.
Scope note: with overlapping multi-speaker dialogue, loud background music or heavy regional accents, recognition quality drops noticeably. If that describes your material, try a short section in the tool first before deciding to process a batch.
Sentence segmentation and timeline alignment
Subtitles are not just the raw recognition output. Long videos are split into segments, and at each seam a line is treated as one sentence that got cut when "the previous sentence does not end with a period and the gap between the two parts is under 0.3 seconds", then merged back into one cue — avoiding the "half a sentence per subtitle" problem. Each cue also absorbs at most one segment, so a punctuation-free voice-over cannot be merged into one long subtitle and lose its sentence-by-sentence value.
Translation is not done line by line in isolation either — the surrounding context is included so pronouns and tone stay consistent.
Multi-language translation and glossary
Subtitle translation connects to a professional translation API and currently supports translation between 20 languages including Chinese, English, Japanese and Korean. For words where a mistake matters — brand names, product names, model numbers — you can pin the translation down first with a glossary: the machine translation then outputs the wording you specified instead of deciding on its own.
Free online subtitle tools (no sign-up)
All 10 tools work without signing in, and 8 of them run locally in the browser, so neither the SRT file nor the video is uploaded to a server. If you only want to edit a subtitle file and would rather skip the full "upload a video, get a finished video" flow, this is the shortest way in.
Subtitle translator
Upload an SRT, pick your languages, download the translated file. 20 languages supported, no sign-up needed.
Bilingual subtitles
Turn an SRT into a bilingual file with the original on top and the translation underneath — ready to hand to a proofreader.
SRT to VTT
Convert between SRT and WebVTT. YouTube and web players only accept VTT; most desktop players prefer SRT.
SRT to ASS
Convert SRT into styled ASS subtitles: start from 10 templates, fine-tune size, colour, outline and background box, then add fade-in or per-character reveal animation.
Fix subtitle timing
Subtitles a few seconds early or late, or a total duration that does not match the video? Fix it in one go — shift everything, or scale by a ratio.
Subtitle QC
Check line length, on-screen duration and reading speed against platform subtitle guidelines, with every issue listed.
Batch find & replace
Fix typos and inconsistent terminology in bulk. Only the subtitle text changes — timing, numbering and inline tags are kept exactly as they were, and every change is listed for confirmation first.
SRT to plain text
Pull just the dialogue out of an SRT as plain text — for writing scripts, taking notes, or getting a quote from a translation agency.
Clean up SRT
Clean up overlapping timings, adjacent duplicate lines, stray blank lines and broken numbering, and get a well-formed SRT back.
Reframe video
Turn a 16:9 video into 9:16 or 1:1 and let the subtitles reflow into the new safe area, with line breaks matched to the new width. Runs entirely in your browser — the video is never uploaded.
Video localization guides
How to make bilingual subtitles, the subtitle specs for each platform, and the localization workflow for cross-border product videos are all set out step by step in the guides.
- Video localization checklist —— Tick off every item from script to publish
- How to make a bilingual subtitle file —— SRT / VTT / ASS compared
- Burn-in or soft subtitles —— Hardcoded, soft and sidecar subtitles compared
- Amazon product video subtitles —— Specs, sizes and multi-language fit
- How to add bilingual subtitles to TikTok videos —— Three methods compared
- How to estimate subtitle translation cost —— Human, machine and tool routes
What problem does this tool solve
When you put a Chinese product video in front of an overseas audience, the time sink is never the act of "adding subtitles" itself; it is three things stacked together: turning the voice-over into accurate text, translating it into the target market language without terminology mistakes, and combining the subtitles and the picture into one file you can upload directly. Get any one link wrong and the rework happens at the very end of the chain.
The common placements for a video going global are landscape long-form, 9:16 vertical short-form and 1:1 square, and the subtitle safe area differs across aspect ratios for the same material. Subtitles that sit along the bottom edge in landscape can be covered by interface elements in vertical — so leaving padding for the narrowest safe area is the simplest approach. For how much margin to leave and how much of the frame height the font should take in each ratio, see the conversion method inSetting font size by frame-height ratio.
The more languages you need, the less you should translate line by line by hand. Subtitle translation has an easily overlooked precondition: the numbering and the timeline must be preserved exactly, and only the text changes. Once there are many lines, copy-pasting line by line almost always ends in drift, showing up as a whole-file offset or a few swapped lines that are hard to spot by eye. A subtitle-specific tool can parse the structure first, send only the text for translation and reassemble it on the original timeline, leaving this risk to the tool.
Whether to use hardcoded or soft subtitles depends on how many places the video goes: if you only publish on platforms that support a separate subtitle track, soft subtitles are more flexible; the moment it also goes elsewhere, you need a version with the subtitles burned into the picture. The full comparison of the two forms is inBurn-in subtitles or soft subtitles.