How to Translate Subtitle Files Online: SRT, VTT, ASS & SSA

Subtitle translation is a unique challenge. Unlike translating a document where you just need accurate meaning, subtitle translation must also preserve exact timecodes, line breaks, and format-specific markup. Move a colon or alter a timestamp by accident, and the subtitle file is broken.

This guide covers the major subtitle formats, what AI subtitle translation can handle, and what to watch for.

Subtitle File Formats Explained

SRT (SubRip Text)

The most common subtitle format. Each entry has a sequence number, a time range, and the subtitle text:

1
00:00:01,500 --> 00:00:04,000
Welcome to the tutorial.

2
00:00:04,500 --> 00:00:08,000
Today we'll cover the basics.

SRT is supported by virtually every video player and platform. The timecodes are in HH:MM:SS,mmm format (comma, not period, before milliseconds — a common point of confusion).

VTT (WebVTT)

The web standard for subtitles, used by HTML5 video elements. Similar to SRT but uses periods instead of commas in timestamps, and supports additional features like cue settings for positioning and styling. VTT files can also include NOTE and STYLE blocks that should be preserved but not translated.

ASS / SSA (Advanced SubStation Alpha)

A more complex format commonly used in anime fansubs and professional productions. ASS supports rich styling: fonts, colors, borders, and positioning. The format has multiple sections (Script Info, Styles, Events) and inline style tags like {\an8} for alignment and {\b1} for bold. Only the dialogue text should be translated — everything else must stay intact.

Why Subtitle Translation Is Technically Tricky

Several things can go wrong when translating subtitles naively:

• Timecode corruption — If a tool modifies the timecode lines, the subtitle sync breaks for the entire file.
• Line count changes — Some subtitle entries span two lines. If the translation adds a third line, some players will cut it off.
• Sequence number errors — SRT requires consecutive numbering. Tools that renumber entries incorrectly will break compatibility.
• Inline tag destruction — ASS files contain styling tags inline with text. Translating the tag content along with the text breaks the formatting.
• BOM and encoding issues — Subtitle files sometimes include a byte order mark (BOM) at the start. Tools that strip or mishandle it cause player compatibility issues.

How AI Subtitle Translation Should Work

A proper subtitle translation tool:

1. Parses the subtitle file into individual entries, separating timecodes from dialogue text.
2. Translates only the dialogue text, leaving timecodes, sequence numbers, and format-specific markup untouched.
3. Reassembles the file in the original format, preserving BOM, line endings, and all structural elements.

Batch processing with controlled chunk sizes ensures context is maintained across adjacent lines — important for dialogue that references something said in the previous subtitle.

Practical Use Cases

• Video course localization — Online courses with English subtitles need translations to reach non-English markets.
• Film and TV subtitling — Independent films and documentaries need subtitle files for international distribution.
• Corporate training videos — Internal training content distributed globally needs subtitles in each office's language.
• YouTube and streaming content — Content creators reaching international audiences benefit from translated subtitle files for auto-caption upload.

Translate Your Subtitle Files — Online

Glot's Subtitle Translate supports SRT, VTT, ASS, and SSA formats. Upload your subtitle file, select the target language, and get a side-by-side view of the original and translated lines with their timecodes. Download the result in the original format with all timecodes and formatting preserved.

Pricing is per subtitle entry. A typical 90-minute movie might have 800–1200 entries — that's a few cents at standard rates.

Subtitle translation combines the precision of format handling with the nuance of natural language translation. AI handles both the technical parsing and the translation quality needed to produce subtitle files that actually work in players and accurately convey the original meaning.