Subtitling conventions are useful as a guideline to editing subtitles and providing legibility. These conventions are sometimes challenged because of the evolving nature of subtitling and, most probably, with the evolution of on-screen media and technology. Listed below are subtitling conventions from various sources.
NEL 4 SUBTITLING GUIDELINESfor foreign-language programmes http://www.channel4.com/media/documents/corporate/foi-docs/SG_FLP.pdf
A Proposed Set of Subtitling Standards in Europe by Fotios Karamitroglou
According to Karamitroglou the following categories can be elided:
Jorge Díaz Cintas. Subtitling Theory, Practice, and Research https://www.researchgate.net/publication/314278174_Subtitling_theory_practice_and_research [accessed Feb 19 2019].