iPhone · Research guidance. Instructions are based on publisher guidance; a UK IPTV account was not tested on this platform.
Check programme and app support
Apple documents subtitles and captions in supported video apps and qualifies track availability. First enable the appropriate available track in the player. A system preference should not be described as supplying SDH or another language for every title. The programme and app determine which choices actually exist.
Open Subtitles and Captioning
Use Settings, Accessibility, Subtitles & Captioning. Apple documents Closed Captions + SDH as a preference for those accessible tracks when available. Read that availability condition before expecting it to change a programme that has no suitable track. It is different from enabling a general speech-transcription overlay.
Choose or create a style
Open Style and inspect an existing choice or create one using the documented font, size, colour, background and edge options. Start with a readable contrast and a moderate size. Do not adjust several unrelated visual-accessibility controls at once, because it becomes harder to identify which setting affected the captions.
Compare the actual player
Return to the same short passage in the supported app and inspect the result. Check whether the text fits and whether its background obscures important information. If a custom app uses another caption renderer, consult that app’s documented settings instead of assuming the iPhone style must govern every visible text layer.
Name generated text accurately
Current iPhone documentation also distinguishes Transcribed and Translated subtitle labels in eligible iOS 27 contexts with model and language limits. Those are not interchangeable with every supplied SDH track. A useful report identifies the label and text source as well as the style, without claiming that all devices or programmes support generation or translation.
Questions, answered
Does Closed Captions + SDH guarantee an SDH track?
No. Apple states that the preference applies when those captions are available.
Is this the same setting as general Live Captions?
No. Identify the specific subtitle or caption feature in use.