What Is an STL File?
Everything you need to know about the EBU STL (Tech 3264) subtitle format, the European broadcast standard for professional subtitle exchange.
STL (EBU SubTitling List) is a binary subtitle file format defined by the European Broadcasting Union in technical specification EBU Tech 3264 (1991). It is the standard subtitle exchange format for European television broadcasters and is still widely used in broadcast workflows, professional video servers, and post-production environments across Europe.
What Does STL Stand For?
STL stands for Subtitling List file, the extension used for EBU Tech 3264 subtitle files. The EBU (European Broadcasting Union) developed this format in 1991 to standardize subtitle exchange between different broadcasting systems. Despite its age, STL remains in active use because many professional broadcast systems, video servers, and compliance workflows still require it.
How STL Files Work
An STL file is a binary file divided into two main blocks: the Global Storage Block (GSI) containing metadata like the subtitle language, editor, and timing format, and the Text and Timing Information Block (TTI) containing the actual subtitle entries with their timecodes and text. Each TTI entry has a cumulative status flag, a timecode in HH:MM:SS:FF format, and text that can include special EBU character codes for accents and positioning.
When to Use STL
STL is the right choice when you are working with European broadcast television, delivering subtitles to systems that require EBU Tech 3264 compliance, or interfacing with professional video servers and playout automation. Many European broadcasters, content distributors, and post-production facilities still mandate STL as their delivery format.
STL File Structure
[GSI Block - 1024 bytes] Code Page Number: 850 Character Code Table: 0 (Latin) Language Code: eng Original Programme Title: Example Show [TTI Block - variable entries] Each entry: SGN (2 bytes) - subtitle group number SN (2 bytes) - subtitle number TCI (5 bytes) - timecode in (HH:MM:SS:FF) TCO (5 bytes) - timecode out VP (1 byte) - vertical position TF (112 bytes) - text field
Advantages of STL
- European broadcast standard (EBU Tech 3264) for subtitle exchange
- Supports multiple character code tables for different languages
- Carries rich metadata (editor, language, revision, programme title)
- Frame-accurate timing compatible with professional video servers
Limitations of STL
- Binary format - cannot be read or edited in a standard text editor
- Limited to 112 bytes of text per subtitle block
- Frame-based timecodes require knowing the exact video frame rate
- Older format with character tables that differ from modern Unicode
Players and Platforms That Support STL
STL Frequently Asked Questions
How do I open an STL file?
STL files are binary, so they cannot be opened meaningfully in a standard text editor. Use Subtitle Edit (free, open source) or a professional video editing tool to open, view, and edit STL subtitles. You can also convert STL to SRT or VTT for easier editing.
What is the difference between STL and SRT?
STL is a binary EBU broadcast format with frame-based timecodes and a 1024-byte metadata header. SRT is a plain-text format with millisecond timecodes and no metadata. STL is for European broadcast delivery; SRT is for general video use and is far more widely supported.
Why does my STL file have garbled text?
STL uses different EBU character code tables (Latin, Cyrillic, Arabic, etc.). If the code table in the file does not match the text content, characters may appear garbled. Converting to SRT with the correct codepage resolves this for modern use.
What frame rate should I use when converting STL?
STL timecodes are frame-based. You must know the original video frame rate (commonly 25 fps for European PAL broadcast). If you convert at the wrong frame rate, subtitle timing will drift.