56 lines
2.3 KiB
Markdown
56 lines
2.3 KiB
Markdown
# Subtitle Preview Scale Design
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**Goal:** Make the subtitle sample inside the small preview screen visually proportional by scaling the rendered preview text down, while keeping the real subtitle size values unchanged for export and editing.
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## Context
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The current subtitle defaults card renders the preview text using the raw subtitle font size value. In a compact sample screen, that makes the text appear nearly as tall as the preview display itself, which breaks visual proportion and makes the mock preview feel unrealistic.
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The user approved the "preview scale mapping" direction instead of enlarging the screen or rebuilding the preview as a strict video-canvas simulator.
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## Approved Direction
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- keep the stored subtitle size value unchanged
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- keep the slider values unchanged
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- keep exported subtitle defaults unchanged
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- only scale the preview rendering inside the small sample screen
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- make the preview text visually smaller relative to the sample screen
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## Recommended Behavior
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Use a lightweight preview-only mapping:
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- compute a preview font size from the real subtitle size
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- apply a clamp so small values do not become unreadable
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- keep the label beside the slider showing the real value such as `24px`
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- keep upload/export using the real value such as `24`
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This preserves the product meaning of the controls while making the small preview believable.
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## Rendering Rules
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- real subtitle size remains the source of truth in state
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- preview font size is a derived value for UI only
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- preview outline strength should scale down with the preview text so the stroke does not overpower the sample
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- subtitle bottom offset behavior remains unchanged
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## Testing Strategy
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Update upload-screen tests to verify:
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- the preview text no longer renders at the raw `24px` size
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- the slider can still change the real font size value
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- the preview updates to the mapped display size
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- upload confirmation still sends the unmodified real subtitle size
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## Out of Scope
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- changing the export subtitle engine
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- changing slider ranges
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- redesigning the subtitle defaults card
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- introducing full video-canvas simulation
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## Success Criteria
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Success means the sample subtitle looks appropriately smaller than the preview screen, while the UI still communicates and submits the real subtitle size values unchanged.
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