Convert ASS to TTML Online Free

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Converts to TTML on secure servers · first daily conversion free · no signup

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Convert ASS subtitle files to W3C TTML XML format for professional broadcast and streaming platform delivery. ChangeThisFile handles the conversion server-side and auto-deletes your file.

By ChangeThisFile Team · Last updated: March 2026

Quick Answer

ChangeThisFile converts ASS to TTML on a secure server. Upload your ASS subtitle file and it is converted to W3C TTML XML with proper namespaces and begin/end attributes. Files are auto-deleted after conversion. Free with no signup required.

First daily conversion free No signup required Encrypted transfer · Async jobs kept up to 24h Queued when needed Updated May 2026

ASS vs TTML: Format Comparison

Key differences between the two formats

Feature	ASS	TTML
Structure	Plain text with [Script Info] and [Events] blocks	XML with namespace declarations
Styling	Inline style tags with \b, \i, \c syntax	XML tts:* attributes in style elements
Positioning	\pos(x,y) coordinates	Named region elements with tts:origin
Broadcast compatibility	Consumer players only	Professional broadcast and streaming
Karaoke support	Full syllable-level timing	No native karaoke support
File size	Compact	Larger due to XML overhead
Best for	Anime and styled consumer video	Netflix, Amazon, broadcast delivery

When to Convert

Common scenarios where this conversion is useful

Submitting to broadcast and streaming platforms

Netflix, Amazon Prime, and Disney+ require TTML-based subtitle formats for professional delivery. Converting ASS to TTML is the first step toward meeting professional subtitle specifications.

Integrating with NLE broadcast workflows

Professional non-linear editors and broadcast subtitle systems like EZTitles and Cavena work with TTML. Converting ASS to TTML allows fansub-quality timing to be imported into professional toolchains.

MPEG-DASH and HLS streaming

Adaptive streaming formats like MPEG-DASH support TTML as a subtitle sidecar. Converting ASS to TTML enables subtitle delivery alongside fragmented video streams.

Who Uses This Conversion

Tailored guidance for different workflows

Video Editors & Subtitlers

Convert ASS caption files to TTML for the subtitle track your editor or delivery spec requires
Move ASS subtitles into TTML to hand off to an editor working in a different tool

After converting to TTML, confirm the cue timings still line up with the video

Check that line breaks and special characters survived the ASS to TTML conversion

Content Creators & YouTubers

Convert ASS captions to TTML to upload alongside your video on YouTube, Vimeo, or social platforms
Turn a ASS caption file into TTML to make your video clearer and more accessible

Keep individual TTML cues short (about one to two lines) so captions stay readable on screen

Preview the TTML captions on the actual video to catch any timing drift before publishing

Accessibility & Localization Teams

Convert ASS subtitles to TTML to meet the caption format an accessibility or compliance spec requires
Prepare ASS captions as TTML to hand to translators or a localization workflow

Speaker labels and on-screen positioning only carry over if TTML supports them, so spot-check the result

Validate the TTML file in a caption checker to catch overlapping cues or malformed timestamps

How to Convert ASS to TTML

1

Upload your ASS file

Drag and drop your ASS subtitle file onto the converter, or click browse to select it. The file is transferred over an encrypted connection.
2

Server-side conversion

The server parses each ASS dialogue line, converts timestamps to TTML's HH:MM:SS.mmm format, strips ASS styling tags, and produces a well-formed TTML XML document.
3

Download the TTML

Save your converted TTML file. The server copy is automatically deleted after processing.

Automate this conversion

Convert ASS to TTML via API

Integrate this conversion into your pipeline with 3 lines of code. Free tier: 25 conversions/month.

curl -X POST https://changethisfile.com/v1/convert \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -F "file=@input.ass" \
  -F "target=ttml" \
  -o output.ttml --fail

const form = new FormData();
form.append('file', fileInput.files[0]);
form.append('target', 'ttml');

const res = await fetch('https://changethisfile.com/v1/convert', {
  method: 'POST',
  headers: { 'Authorization': 'Bearer YOUR_API_KEY' },
  body: form
});
const blob = await res.blob(); // your converted TTML file

Replace YOUR_API_KEY with your free key — no credit card needed.

Get a free API key

Frequently Asked Questions

What is TTML used for?

TTML (Timed Text Markup Language) is the W3C standard for subtitle interchange. It is used by Netflix, Amazon, Disney+, BBC, and broadcast networks for professional subtitle delivery and accessibility compliance.

Will ASS styling be preserved in TTML?

Basic timing and text content are preserved. ASS-specific styling (\b, \i, \c, \pos) is stripped during conversion. The resulting TTML uses plain text p elements without tts styling attributes.

Is the TTML output W3C standards-compliant?

Yes. The output conforms to W3C TTML 1.0 with standard tt, head, body, div, and p elements and xmlns namespace declarations.

What does ASS karaoke timing become in TTML?

Karaoke syllable timing (\k, \K) is dropped. TTML does not support karaoke. Only cue-level begin and end attributes are preserved.

Will the TTML work for Netflix or Amazon submission?

Netflix (IMSC-1) and Amazon use strict TTML profiles requiring specific region and styling attributes. The basic TTML output from this converter may need additional editing to meet exact delivery specs.

Are my files deleted after conversion?

Yes. Files are transferred over HTTPS and automatically deleted from the server after the TTML is ready for download.

What timestamp format does TTML use?

TTML uses HH:MM:SS.mmm format for begin and end attributes on each p element, e.g. begin="00:01:23.456" end="00:01:26.789".

Is there a file size limit?

Subtitle files are plain text. The 50 MB server limit is not a concern for ASS files.

Can I convert TTML back to ASS?

Yes. ChangeThisFile supports TTML to ASS conversion for round-tripping between formats.

Can I validate the TTML output?

Yes. The XML output is well-formed and can be validated with any XML parser. For TTML-specific compliance, use the W3C TTML validator.

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