TTML vs STL: Which Format Is Right for You?
A complete comparison of Timed Text Markup Language (TTML) and Spruce Subtitle (STL), covering structure, timestamps, styling, platform support, and best use cases.
TTML (Timed Text Markup Language) and STL (Spruce Subtitle) serve different roles in the subtitle ecosystem. Timed Text Markup Language is designed for professional subtitle delivery, streaming compliance. Spruce Subtitle is designed for dvd subtitle creation and authoring. Understanding their differences helps you choose the right format for your workflow and avoid compatibility problems.
TTML vs STL at a Glance
| Feature | TTML (Timed Text Markup Language) | STL (Spruce Subtitle) |
|---|---|---|
| File extension | .ttml | .stl |
| Designed for | Broadcast, streaming platforms, professional workflows | DVD authoring (Spruce/Apple DVD Studio Pro) |
| Timestamp format | X.YYYs (seconds) or HH:MM:SS.mmm (clock) | HH:MM:SS:FF (SMPTE timecode) |
| Time precision | Millisecond (3 digits) or better | Frame-based (25fps PAL or 29.97fps NTSC) |
| Styling support | Extensive (CSS-like, regions, animation) | Limited (italic, position via control codes) |
| Header required | XML declaration and root with namespaces | // Spruce Subtitle File comment |
| Positioning | Full region-based positioning | Basic position control for DVD subtitles |
| Multi-line breaks | tags within elements | Pipe character (|) for line breaks |
| Standardized | W3C / SMPTE standardized (TTML 1.0, TTML2, IMSC) | Spruce/Apple format, widely used in DVD authoring |
| Browser support | Moderate (via JavaScript players, not native HTML5) | Poor (DVD-specific format) |
| Encoding | UTF-8 (always) | ANSI or UTF-8 |
| Primary use case | Professional subtitle delivery, streaming compliance | DVD subtitle creation and authoring |
Key Differences Explained
Timestamp and Timing
TTML uses x.yyys (seconds) or hh:mm:ss.mmm (clock). STL uses hh:mm:ss:ff (smpte timecode). TTML offers millisecond (3 digits) or better precision, while STL works at frame-based (25fps pal or 29.97fps ntsc) precision. When converting between these formats, some timing precision may be lost due to the different granularity.
Structure and Syntax
TTML files use xml document with and sections. Each cue follows the pattern:
text
in xml. In contrast, STL files use header comment, then comma-delimited lines, where each cue looks like: comma-delimited: start time, end time, text. The structural difference means conversion requires parsing and reformatting, not a simple text replacement.Styling and Visual Control
TTML provides extensive (css-like, regions, animation). STL provides limited (italic, position via control codes). TTML has stronger styling support, making it the better choice when visual appearance matters.
Platform and Player Support
TTML is industry standard for netflix, amazon, apple tv. STL is common in dvd authoring workflows. Their browser and device support profiles differ significantly, which is often the deciding factor when choosing between them.
When to Use TTML
Choose TTML when your priority is professional subtitle delivery, streaming compliance. It excels in netflix, amazon prime, apple tv, broadcast and was w3c timed text working group, based on xml. TTML's biggest advantage is its rich styling capabilities. Its main limitation is that it complex xml structure, large file size, steep learning curve.
When to Use STL
Choose STL when you need dvd subtitle creation and authoring. It is designed for dvd authoring, legacy video production and was created for spruce technologies dvd authoring tools. STL's standout strength is its specialized role in its target use case. Be aware that it dvd-specific, limited modern relevance.
Converting Between TTML and STL
Our free TTML to STL converter handles the structural and timing differences automatically. The converter translates TTML timing to STL timing, with minimal rounding where needed. Styling that the target format cannot represent is normalized or stripped, so you always get valid, ready-to-use output.
Frequently Asked Questions
Is TTML better than STL?
Neither format is universally better. TTML is better for professional subtitle delivery, streaming compliance. STL is better for dvd subtitle creation and authoring. Choose based on your target platform and workflow, not on which format is technically superior.
Can I convert TTML to STL without losing quality?
Yes. Text content is always preserved during conversion. Timing is preserved to the target format precision, with minimal rounding at the centisecond or frame level where needed. Styling features that the target does not support are dropped, but the subtitle text and timing remain accurate.
Which format is more widely supported?
STL has broader support across players and devices. TTML works well with moderate (via javascript players, not native html5), while STL works with poor (dvd-specific format). If you are unsure which format to use, STL is usually the safer choice for maximum compatibility.
Are TTML and STL files compatible?
Not directly. TTML and STL use different file structures and timestamp formats. A player that supports one may not support the other. Use a converter to switch between them. Most modern subtitle editors and our converter can handle the conversion in both directions.