# Thai subtitles from word timestamps A Thai sentence has no spaces to cut a subtitle at. How word timestamps give a cue its cut points, the rules a Thai cue file needs, and the convention to ask for. Published 2026-09-09. Paxa Labs. A subtitle is a transcript cut into pieces that fit on a screen for the seconds they are spoken. In English the cutting is easy. A cue ends at a space, and a tool that knows nothing about the language produces readable lines. Thai writes a whole phrase as one run of characters. A tool that cuts at a character count cuts through a word, and the viewer reads half a word on one line and the other half two seconds later. This post shows how to build Thai cues from the word timestamps Paxa STT Lite returns. Each span is a whole Thai word with its start and end, which is exactly the set of places a cue may be cut. The rules for turning spans into cues fit on one page, and the result is a subtitle file any player reads. ## What a span is Ask for `timestamps` set to `"word"` and the response carries a `words` array beside the transcript. Each entry is one word with its start and end in seconds. For Thai the words are segmented on the way out. A span covers a whole word and never a character. The spans join back into the transcript with nothing lost. curl: ```bash AUDIO=$(base64 < meeting.m4a | tr -d '\n') curl -X POST https://api.paxalabs.com/v1/stt \ --max-time 300 \ -H "Authorization: Bearer $PAXA_API_KEY" \ -H "Content-Type: application/json" \ -d "{\"audio\": \"$AUDIO\", \"model\": \"paxa-stt-lite-v1-preview\", \"timestamps\": \"word\"}" ``` Response: ```json { "text": "สวัสดีค่ะคุณสมชายยอดชำระของท่านจำนวน พันสองร้อยห้าสิบ บาทครบกำหนดวันที่ สิบห้า สิงหาคมนี้ชำระผ่านแอปได้ตลอด ยี่สิบสี่ ชั่วโมงค่ะ", "words": [ { "text": "สวัสดี", "start": 0.12, "end": 0.44 }, { "text": "ค่ะ", "start": 0.52, "end": 0.66 }, { "text": "คุณ", "start": 1.08, "end": 1.24 }, { "text": "สมชาย", "start": 1.32, "end": 1.88 }, { "text": "ยอด", "start": 2.36, "end": 2.56 }, { "text": "ชำระ", "start": 2.6, "end": 2.879 }, { "text": "ของ", "start": 3, "end": 3.14 }, { "text": "ท่าน", "start": 3.2, "end": 3.359 }, { "text": "จำนวน", "start": 3.48, "end": 3.879 }, { "text": "พันสองร้อยห้าสิบ", "start": 4.24, "end": 5.4 }, { "text": "บาท", "start": 5.56, "end": 5.759 }, { "text": "ครบ", "start": 6.32, "end": 6.52 }, { "text": "กำหนด", "start": 6.56, "end": 6.84 }, { "text": "วัน", "start": 6.92, "end": 7.039 }, { "text": "ที่", "start": 7.04, "end": 7.119 }, { "text": "สิบห้า", "start": 7.24, "end": 7.48 }, { "text": "สิงหาคม", "start": 7.68, "end": 8.26 }, { "text": "นี้", "start": 8.36, "end": 8.5 }, { "text": "ชำระ", "start": 9.08, "end": 9.36 }, { "text": "ผ่าน", "start": 9.48, "end": 9.68 }, { "text": "แอป", "start": 9.76, "end": 9.92 }, { "text": "ได้", "start": 10, "end": 10.14 }, { "text": "ตลอด", "start": 10.2, "end": 10.46 }, { "text": "ยี่สิบสี่", "start": 10.56, "end": 10.96 }, { "text": "ชั่วโมง", "start": 11.08, "end": 11.4 }, { "text": "ค่ะ", "start": 11.52, "end": 11.66 } ], "usage": { "seconds": 11.952, "credits": 1.66 } } ``` ## Cutting spans into cues Walk the spans in order and collect them into a cue until one of three limits is reached. The cue then ends at the last span's end, and the next cue starts at the next span's start. - Length. A Thai line reads comfortably at around thirty-five characters, and a cue holds at most two lines. Count the characters of the collected words and cut before the word that would push past the limit. - Duration. A cue on screen for longer than about six seconds reads as stuck. Cut when the next word would push the cue past the limit, even when the line has room. - Pause. A gap between one span's end and the next span's start longer than about half a second is a breath or a full stop. Cut there, and the cue ends when the speaker does. A cue that ends at a pause reads better than one that ends at a count. A small overrun of the length limit to reach a pause is worth allowing. Where a cue has two lines, break the line at the widest gap between spans inside the cue, which is usually a phrase boundary. one sentence, two cues: ``` words วันนี้ 0.00 0.38 เรา 0.38 0.55 จะ 0.55 0.70 คุย 0.70 0.98 เรื่อง 0.98 1.30 งบประมาณ 1.30 1.92 ปีหน้า 1.92 2.40 กัน 2.40 2.61 นะครับ 2.61 3.05 cues 1 00:00:00,000 --> 00:00:01,300 วันนี้เราจะคุยเรื่อง 2 00:00:01,300 --> 00:00:03,050 งบประมาณปีหน้ากันนะครับ ``` ## The convention to ask for Subtitles want the spoken convention, which is the default. The viewer hears สองพันสามร้อยห้าสิบบาท and reads the same words. A digit on screen while the speaker says seven syllables reads as a mismatch, and a cue built from the written form also loses the span boundaries inside a number, since the digits arrive as one token. Keep the verbatim style for the same reason. A viewer who hears a false start and reads a cleaned sentence notices. The clean style is for a transcript read on its own, away from the audio. ## Writing the file SRT numbers each cue, writes the start and end as hours, minutes, seconds, and milliseconds with a comma before the milliseconds, and follows with the text. WebVTT is the same with a period before the milliseconds and a header line. Both are plain text, and both carry Thai as UTF-8 with no further setting. Write the seconds from the spans with three decimals and the file is done. For a translated track, send the cues' text to the translation API one cue per segment with the ids echoed back. The timings stay with the ids. A Thai video gets an English track with the same cut points, and the two tracks stay aligned. ## Next steps - Read the [transcription guide](https://paxalabs.com/docs/speech-to-text#timestamps) for the word timestamps beside the model's own spans on one recording. - Read the [timestamps page](https://paxalabs.com/docs/timestamps) for the span shape shared with speech synthesis, where the same rules build read-along captions. - Read the [numbers post](https://paxalabs.com/guides/thai-transcript-numbers-spoken-or-written) for why a subtitle keeps the spoken form. - Read the [captions use case](https://paxalabs.com/use-cases/captions) for a caption pipeline end to end and what a season of video costs.