What about the reading speed threshold for dialogue or forced narrative heavy content (docs, unscripted)?
When on-screen text and dialogue overlap, precedence should be given to the most plot pertinent message. Avoid over truncating or severely reducing reading speed in order to include both dialogue and on-screen text.
For documentaries in particular, our Timed Text Style Guide calls for only adding the speaker’s title once, the first time the speaker appears in the documentary.
For dialogue-heavy scenes, truncation should be used in combination with timing adjustments to allow the message to be conveyed with appropriate reading speed. The timing guidelines in our Style Guide allow for extending the out-time of the subtitle up to 12 frames (0.5 second) to accommodate for reading speed. We understand achieving this balance is no easy task, but this is ultimately what subtitling is about.