overlookmotel wrote: ↑Thu Jun 08, 2023 8:00 pm
I am less fine with secrecy about the reasoning behind any particular decision. What's to be ashamed of?
The trouble is, someone has to pinpoint a specific server/manufacturers weakness. That is something that wasn't to happen on public ISDCF events/let even persist in meeting notes. Those specific limitations 'creeped' into the standards and constraints, because some people knew about those weaknesses from their daily work.
However - in this specific case, if you google 'subtitles 2 frame gap', you find so many references to this rule from all different sources, that it simply seems to have become a general rule even outside the DCP domain.
Though I don't recall the details leading to the 2 frame gap between subtitles, I believe most of the recommendations in the document are due to issues with some equipment based on ISDCF tests.
In designing the USL/QSC closed captioning equipment, I had to deal with zero frame gaps between captions. When I discovered there was no gap between captions, I would write the new caption over the old one without first blanking the screen to get rid of the old caption. This was required as part of an ISDCF test where a caption (or subtitle) spanned a reel boundary. When it is desired to have a caption span a reel boundary, the TimeOut is set to the last frame of the first reel, and the caption is repeated in the next reel with TimeIn being the first frame of the reel. The ISDCF test checked to make sure the caption spanning the reel boundary did not flash.
The SMPTE RDD52 is a Registered Document Disclosure developed by the listed sponsors and ISDCF. An RDD is typically a disclosure by a company of a proprietary protocol to allow others to communicate with that equipment. Here, ISDCF and the sponsors released the RDD in an effort to improve interoperability based on ISDCF Plugfests.