This spec seems to supersede OggMNG (which is good, since this spec seems much more likely to be implemented), but isn't written with one of OggMNG's use cases in mind, namely graphical subtitles and other kinds of overlays on another video stream. To support this case, you at least need the ability to specify a transparent background colour, which seems trivial enough. Some means of specifying whether an OggSpots stream is intended to be an overlay or not might also be nice, and this was discussed briefly in the OggMNG spec, but no decision was reached.
Anyhoo, I think that this is an important feature for this kind of codec, so I just wanted to chime in and make sure it wasn't forgotten. Subtitle support in Thoggen for instance, is blocking on this capability.
I don't think OggSpots is supposed to replace OggMNG in any way -- Jmspeex 16:41, 22 February 2006 (PST)
That's fair, though I don't see any compelling technical reasons for OggMNG if OggSpots gets off the ground. I merely wanted to point out that graphical subtitles and overlays would be a nice use for OggSpots, if the spec took them into acount, which seems like it would take only a minimal effort. -- Jdoda 19:59, 22 February 2006 (PST)
I came to OggSpots looking for a bitmap overlay format. I would like to raise a few points.
- What is the format of the BG-color fields? The BG-color field in the header is four bytes; if these are RGBA, there is already a simple way to specify a transparent background color.
- How to mark the end of an overlay? Stand-alone images stay until the next image starts, but overlays may end earlier. An empty image packet could do the job.
- Metadata? Would it be useful to add a comment packet, or is metadata provided by OggSkeleton enough? And would it be useful to specify some standard key (maybe lang/language and type=overlay)?