In the case that the subtitles were initially authored for teletext and converted, the derived subtitle formats are constrained to the same character sets.
ɪnðə kˈeɪs ðætðə sˈʌbtaɪɾəlz wɜːɹ ɪnˈɪʃəli ˈɔːθɚd fɔːɹ tˈɛlᵻtˌɛkst ænd kənvˈɜːɾᵻd, ðə dᵻɹˈaɪvd sˈʌbtaɪɾəl fˈɔːɹmæts ɑːɹ kənstɹˈeɪnd tə ðə sˈeɪm kˈæɹɪktɚ sˈɛts.