Add IMSC 1.1 image profile image-based export#12547
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IMSC 1.1 image profile (W3C/ISO TTML image profile) is the standardized image-subtitle carriage for streaming and broadcast delivery. It was the one widely-used image-based export SE lacked. ExportHandlerImscImage writes a single self-contained TTML file: each cue is a cropped PNG embedded as a base64 <smpte:image> in the head, referenced from a <div smpte:backgroundImage> in the body, positioned by a per-cue region with percentage origin/extent computed from the cue's on-screen placement (same alignment/override logic as the BDN XML handler). Media timebase, HH:MM:SS.mmm times. Reuses the shared ImageRenderer, so it picks up the export dialog's font/outline/box/position settings for free. Wired into the File > Export menu and the image-based export dialog; the output round-trips through SE's own Timed Text Base64 Image reader. Verified: 3 libuilogic tests (conformant profile/timebase/smpte shape, round-trip through the base64-image reader recovering exact timings, and embedded PNGs decoding to the right dimensions), plus a rendered sample whose extracted PNG shows the correct subtitle. Full solution builds; all libuilogic tests pass. Docs (File features) + change-log updated. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
This was referenced Jul 16, 2026
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Adds the IMSC 1.1 image profile (W3C/ISO TTML image profile) as an image-based export — the standardized image-subtitle carriage used for streaming and broadcast delivery, and the one widely-used image-based format SE didn't have (the gap identified in the EBU-TT-D discussion).
What it produces
ExportHandlerImscImagewrites a single self-contained TTML file:<smpte:image imagetype="PNG" encoding="Base64">in<head>,<div smpte:backgroundImage="#imgN">in<body>withbegin/end,<region>with percentagetts:origin/tts:extentcomputed from the cue's on-screen placement (same alignment +OverridePositionlogic as the BDN XML handler),ttp:profile=".../imsc1/image",ttp:timeBase="media",HH:MM:SS.mmmtimes.It reuses the shared
ImageRenderer, so it inherits the export dialog's font / outline / shadow / box / position settings automatically.Wiring
ExportImageType.ImscImage).Verified
smpte:imageshape, round-trip through the base64-image reader recovering exact timings, and embedded PNGs decoding to the right dimensions.origin 39.58% 87.04%,extent 20.83% 8.33%).Pairs naturally with the EBU-TT-D text format added earlier — together they cover both the text and image TTML profiles European/streaming delivery asks for.
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