IMSC
IMSC (TTML for streaming)
The W3C profile of TTML used by Netflix, Apple, and most streaming services. Combines TTML's styling with HLS/DASH delivery.
In depth
IMSC (Internet Media Subtitles and Captions) is the W3C profile of TTML used as the de facto streaming subtitle format. Netflix, Apple TV, Amazon Prime, and most streaming services accept IMSC for delivery. It supports rich styling (per-region positioning, animation, multiple languages per file) and is the modern successor to TTML / DFXP for streaming workflows. IMSC files are usually delivered alongside HLS (.m3u8) or DASH (.mpd) manifests.
When to use it
Use IMSC when delivering subtitles to a streaming service or building a streaming pipeline. For social, web embed, or YouTube, IMSC is overkill — use SRT or VTT.
Frequently asked
What's the difference between IMSC and TTML?+
IMSC is a subset / profile of TTML. It restricts TTML's full feature set to what's practical for streaming, ensuring interoperability across players.
An XML-based subtitle format used by streaming services and broadcast workflows. Powerful styling and positioning, but verbose.
The W3C web standard for subtitles. Used by HTML5 <track> elements. Like SRT but with dot-separated milliseconds and styling support.
An older subtitle profile of TTML used by Netflix and Adobe Flash. Internally just TTML XML with a .dfxp extension.