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DVD

NTSC DVDs may carry closed captions in the Line 21 format which are automatically sent to the TV and turned on and off by the TV remote or the set-top decoder. Video DVDs may carry closed captions as a bitmap overlay (known as "subtitles") which can be turned on and off via the DVD player – as by selecting a subtitle track labeled either "English for the hearing impaired" or more recently, "SDH" (Subtitled for the Deaf and Hard of hearing). Both Line 21 and DVD bitmap subtitle formats can co-exist on the same DVD, providing two very different methods of displaying captions from the same DVD. On some DVDs, the captions may contain the same text, while on other DVDs, the Line 21 version contains more captions to cover non-speech information than the DVD bitmap subtitles. HD DVD and Blu-ray disc media cannot carry Line 21 closed captions, so SDH subtitles are used as the sole default method.