Having just completed a job which required subtitling, and several conversations with different parties about subtitling and closed captions i thought it would be worth taking a moment to clarify the two.
Firstly EIA 608 closed captions are not subtitles, they are intended for broadcast. Before a caption can be shown it must have been successfully transmitted, and the time it takes to transmit completely depends roughly on the amount of information needing to be displayed. A standard character takes 1 frame transmission time, which compared to subtitles on a DVD is a long time!
We’ve been using Annotation edit for this last job and they provide some very useful guidelines:
1. Keep reading speed constant. Closed captions should have a reading speed at about 15 characters per second.
2. Prefer 2 line captions over 1 line captions. Closed captions allow up to 4 lines.
3. Avoid short one line captions immediately followed by captions with 2 full lines.
You can merge the one line caption with the following one.
4. Every line should be visible at least for 1.5 seconds.
5. The maximum of characters per line is 32.