IMSC
Internet Media Subtitles and Captions
The modern W3C streaming profile of TTML used by Netflix, Apple TV+, Disney+, and most streaming services for caption delivery.
In depth
IMSC (Internet Media Subtitles and Captions) is the current W3C standard profile of TTML designed for streaming and broadcast delivery. It constrains TTML to a practical subset that streaming platforms can render consistently across devices. IMSC 1.0.1 and 1.1 are the most common versions. Netflix, Apple TV+, Disney+, Amazon Prime Video, and most modern OTT platforms use IMSC as their primary caption ingest format.
When to use it
Use IMSC when delivering captions to streaming platforms (Netflix, Apple TV+, Disney+, Amazon), broadcast pipelines, or any professional OTT workflow. For personal projects and social video, SRT or VTT is simpler.
Frequently asked
What's the difference between IMSC and TTML?+
IMSC is a constrained profile of TTML — it uses the same XML structure but limits which features are allowed. This ensures consistent rendering across streaming platforms. Think of IMSC as 'TTML for streaming.'
How do I convert IMSC to SRT?+
Use SoCaptions' IMSC to SRT converter. Paste the XML, get a clean .srt. Styling and positioning are stripped since SRT doesn't support them.
Do I need IMSC for YouTube?+
No — YouTube accepts SRT and VTT. IMSC is for professional streaming platforms (Netflix, Apple TV+, Disney+) and broadcast.
An XML-based subtitle format used by streaming services and broadcast workflows. Powerful styling and positioning, but verbose.
An older subtitle profile of TTML used by Netflix and Adobe Flash. Internally just TTML XML with a .dfxp extension.
Apple's TTML 1.0 profile for subtitles in Final Cut Pro and iTunes Connect (Apple TV+). A strict XML format with limited per-element styling.
The most common subtitle file format. Plain text with numbered cues and HH:MM:SS,mmm timestamps.