Is the VTT to STL converter free?

Yes, completely free with no sign-up, no watermarks, and no file size limits. All processing happens locally in your browser, ensuring your subtitle files never leave your device.

Are VTT NOTE comments preserved in STL?

No. VTT NOTE blocks are developer comments and have no equivalent in STL format. They are stripped during conversion. Only the subtitle cue text and timing are preserved in the STL output.

How are VTT voice tags handled in STL?

VTT voice tags ( ) are used to label dialogue by speaker. STL does not have a native speaker identification system, so speaker labels from voice tags are preserved as plain text within the TTI block text content.

Can I convert VTT to STL for BBC iPlayer content?

Yes. BBC subtitle delivery for broadcast television uses STL format. If you have web-originated VTT subtitles for content that will also air on broadcast TV, convert them to STL for the broadcast delivery workflow.

What character encoding does STL use?

STL uses character code tables defined in the GSI header's CCT field. The converter handles UTF-8 input from VTT files and maps characters to the appropriate STL code table. Accented characters for French, German, Spanish, and other European languages are supported.

Can I edit the STL file after conversion?

STL is a binary format and requires specialized tools like EZTitles, Annotation Edit, Poliscript, or Mac Caption to edit. Unlike VTT (plain text), STL cannot be edited in a standard text editor.

Are timestamps accurate after VTT to STL conversion?

Yes. VTT millisecond timestamps are converted to frame-based STL timecodes. At 25fps, the maximum rounding error is about 20ms (half a frame). This is within acceptable tolerance for broadcast subtitle delivery.

What file extension does STL use?

STL files use the .stl extension, recognized by European broadcast systems and subtitle tools. The format is formally known as EBU Tech 3264.

Absolutely. All conversion happens client-side in your browser. No subtitle data is ever transmitted to a server.

How large are STL files compared to VTT?

STL files are binary and typically 2-4x larger than VTT. Each TTI block is exactly 128 bytes regardless of text length, so short cues consume the same space as long ones.

Does STL support multi-line subtitles from VTT?

Yes. Multi-line VTT cues are preserved as multi-row text within STL TTI blocks. STL supports up to multiple rows per TTI block, and the converter maps VTT line breaks to STL row separators.

Can I batch convert multiple VTT files to STL?

This page converts one file at a time. For batch processing, use the Workspace pipeline to load multiple VTT files and convert them sequentially.

What is the difference between STL and EBU-TT-D for VTT conversion?

STL is the traditional binary format for European broadcast. EBU-TT-D is the newer XML-based format for modern broadcast and streaming. If your target system accepts EBU-TT-D (XML), consider converting VTT to TTML instead of STL for easier editing and compatibility.

VTT to STL Converter

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VTT

WEBVTT
 
00:00:01.000 --> 00:00:04.000
Hello, world!
 
00:00:04.500 --> 00:00:08.000
This is a subtitle file.
 
00:00:08.500 --> 00:00:12.000
Converted locally!

STL

// Spruce Subtitle File
// Format: Start Time, End Time, Subtitle Text
 
00:00:01:00 , 00:00:04:00 , Hello, world!
00:00:04:15 , 00:00:08:00 , This is a subtitle file.
00:00:08:15 , 00:00:12:00 , Converted locally!

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How It Works

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Free Online VTT to STL Converter

Our VTT to STL converter takes web-native WebVTT subtitles and transforms them into EBU STL format for European broadcast television and DVD production. The converter strips the WEBVTT header and cue settings, reads each VTT cue, converts millisecond timestamps to 25fps frame-based timecodes, generates a GSI header block with metadata, maps subtitle text into TDI data blocks, and produces a valid .stl file for European broadcast delivery.

Input Format

VTT

VTT (WebVTT) is the W3C standard subtitle format for web video. A VTT file starts with the literal header WEBVTT on the first line, followed by cue blocks using HH:MM:SS.mmm --> HH:MM:SS.mmm timestamps (period before milliseconds). VTT supports optional cue settings (positioning, alignment, sizing), inline styling tags, NOTE comments, and CSS blocks.

Output Format

STL

STL (EBU STL, Subtitle Transmission List) is a subtitle format standardized by the European Broadcasting Union (EBU Tech 3264) for television subtitling and DVD production. STL files contain a header block (GSI - General Subtitle Information) with metadata like program title, translator, revision, and frame rate, followed by subtitle data entries (TDI - Text Data Information) containing timing, text, and extension data. STL is the standard format for European broadcast workflows, DVD authoring, and DVB subtitling in EBU member countries.

Features

Converts VTT timestamps to 25fps STL frame-based timecodes

Generates a valid EBU STL GSI header block with metadata

Maps VTT cue text into properly formatted TDI data blocks

Strips VTT header, NOTE comments, and cue settings before encoding

Handles UTF-8 to EBU character set mapping where possible

Outputs .stl files compatible with European broadcast and DVD systems

Why Convert?

Web video subtitles authored in VTT need conversion to STL for ingestion by European broadcast playout servers.

Broadcast QC departments reject VTT files; STL with its GSI metadata header is the mandated deliverable for EBU affiliates.

STL's frame-accurate 25fps timing is more precise than VTT's millisecond timing for PAL post-production workflows.

DVD subtitle authoring tools used in PAL regions import STL natively but have no VTT importer.

Converting VTT to STL lets you repurpose streaming-platform subtitles for physical media distribution.

Broadcast compliance tools verify STL TDI blocks against EBU Tech 3264, a standard VTT cannot satisfy.

Archiving web captions as STL preserves them in the format required by European media regulation.

Format Differences

VTT uses a WEBVTT header and cue blocks; STL uses GSI header and TDI data blocks.

VTT uses HH:MM:SS.mmm timestamps; STL uses HH:MM:SS:FF at 25fps.

VTT supports CSS styling and inline tags; STL uses justification and positioning codes.

VTT has NOTE comments and metadata; STL uses the GSI header for metadata.

VTT supports cue positioning; STL uses vertical position codes per entry.

VTT is the web standard; STL is the European broadcast standard.

Common Use Cases

Web-to-Broadcast Pipeline

Convert web-originated VTT subtitles to STL for European television broadcast delivery, bridging web production and broadcast workflows.

DVD Authoring

Import web subtitles into European DVD authoring systems by converting VTT to the STL format they expect.

European Broadcast Delivery

Produce STL files from VTT subtitles for delivery to European broadcasters that require EBU format.

DVB Subtitling

Prepare web subtitle content for DVB workflows that use STL as the source format.

Multi-Format Distribution

Produce both VTT (for web) and STL (for European broadcast) from the same subtitle source.

Subtitle Localization

Convert internationally-produced web subtitles to STL for European localization and broadcast distribution.

Related Formats

VTT (WebVTT)

The input format: web video subtitle standard for HTML5 video and JavaScript players.

SRT (SubRip)

The universal alternative: convert VTT to SRT for broad player compatibility.

SCC (Scenarist Closed Captioning)

The North American broadcast alternative: convert VTT to SCC for US broadcast.

Frequently Asked Questions

Why convert VTT to STL for broadcast delivery?

European broadcasters like BBC, ARD, and France Televisions require EBU STL format for subtitle delivery. If your subtitles are authored as WebVTT for web distribution, you need to convert them to STL binary format before submitting to broadcast workflows.

What happens to VTT cue settings during STL conversion?

VTT cue settings (align, position, line, size) are mapped to STL TTI block fields where possible. STL uses vertical position and justification fields in each TTI block. Some VTT positioning features may be simplified to fit STL's limited positioning model.

What frame rate should I select for VTT to STL?

European broadcast typically uses 25 fps (PAL standard). If your VTT subtitles were authored for 24fps film content, select 24 fps. For North American 29.97fps NTSC content, STL may not be the right format - consider SCC instead.

How does the converter handle the WEBVTT header?

The WEBVTT header and any metadata blocks are stripped during conversion. STL uses a binary GSI (Global Screen Information) header instead, which is generated automatically from the VTT file contents.

How are VTT dot-separated timestamps converted to STL?

VTT timestamps (00:01:30.500) are first parsed, then converted to STL frame-based timecodes (HH:MM:SS:FF format). At 25 fps, 500 milliseconds maps to approximately frame 12-13. The converter handles this conversion for every cue.

Does the converter generate a valid GSI header?

Yes. The converter generates a 1024-byte GSI header with fields for language code, programme title, and creation date. You can edit the GSI header in a specialized STL editor after conversion if you need to add specific broadcast metadata.

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Related Resources

What is VTT?What is STL?