A start for what little public documentation there is for CVD and OGT

subtitles.

doc/subtitles/cvd-subtitles.txt

+$Id: cvd-subtitles.txt,v 1.1 2004/01/04 16:25:00 rocky Exp $
+The following information is culled from information from 
+Julio Sanchez Fernandez (http://subhandler.sourceforge.net)
+by Rocky Bernstein. 
+
+We do not have information on the subtitle format used on CVD's except
+the submux sample code and a couple of samples of dubious
+origin. Thus, the information below is result of reading some code
+whose correctness is not known and some experimentation.
+
+CVD subtitles are different in several ways from SVCD OGT subtitles
+(see see corresponding info on that.)
+
+Image comes first and meta data is at the end.  So that the metadata
+can be found easily, the subtitle packet starts with two bytes
+(everything is big-endian again) that gives the total size of the
+subtitle data and the offset to the metadata - i.e. size of the image
+data plus the four bytes at the beginning.
+
+Data for single screen subtitle may come in several non-contiguous
+packets of a stream. From the scant data on the format, there is only
+only way known to detect the first packet in a subtitle.  The first
+packet seems to have a valid PTS while later packets for the same
+image don't.
+
+Image data comes interlaced and is run-length encoded (RLE). Each
+field is a four-bit nibbles that is further subdivided in a two-bit
+repeat count and a two-bit color number - up to three pixels can be
+described in four bits.  What a 0 repeat count means is unknown.  It
+might be used for RLE extension.  There is a special case of a 0
+repeat count though.  When the full nibble is zero, the rest of the
+line is filled with the color value in the next nibble.  It is unknown
+what happens if the color value is greater than three.  The rest seems
+to use a 4-entries palette.  It is not impossible that the fill-line
+complete case above is not as described and the zero repeat count
+means fill line.  The sample code never produces this, so it may be
+untested.
+
+Here is information given at the start of a subtitle:
+
+SPU size        2 bytes
+metadata offset 2 bytes
+
+Although metadata information does not have to come in a fixed field
+order, every metadata field consists of a tag byte followed by
+parameters. In all cases known, the size including the tag byte is
+exactly four bytes.
+
+code    Meaning 
+----    -------
+0x0c 	Unknown
+
+0x04 	24-bit subtitle duration in 1/90000ths of a second
+
+0x17	upper left x, y position, each a 10-bit value, encoded:
+           x = ((p[1]&0x0f)<<6) + (p[2]>>2)
+           y = ((p[2]&0x03)<<8) + p[3];
+
+0x1f	lower right x, y postion, each a 10-bit (0-1023) value,
+        encoded as above 
+
+0x24    3 bytes primary palette 0 - 1 byte for each of y, u, and v 
+0x25    3 bytes primary palette 1 - 1 byte for each of y, u  and v
+0x26    3 bytes primary palette 2 - 1 byte for each of y, u  and v
+0x27    3 bytes primary palette 3 - 1 byte for each of y, u  and v
+
+0x2c    3 bytes highlight palette 0 - 1 byte for each of y, u, and v 
+0x2d    3 bytes highlight palette 1 - 1 byte for each of y, u  and v
+0x2e    3 bytes highlight palette 2 - 1 byte for each of y, u  and v
+0x2f    3 bytes highlight palette 3 - 1 byte for each of y, u  and v
+
+0x37    3 bytes transparancy for primary palette - 1 byte for each 
+	of y, u  and v
+
+0x3f    3 bytes transparancy for highlight palette - 1 byte for each 
+	of y, u  and v
+
+0x47    Offset to start of even rows of interlaced image.
+0x4f    Offset to start of odd rows of interlaced image.
+
+
+
+
+
+
+
+
+

doc/subtitles/svcd-ogt-subtitles.txt

+$Id: svcd-ogt-subtitles.txt,v 1.1 2004/01/04 16:25:00 rocky Exp $
+The following information is culled from information from 
+Julio Sanchez Fernandez (http://subhandler.sourceforge.net)
+by Rocky Bernstein. 
+
+SVCD subtitles are transported in private streams with id 0x70 (AC3
+has 0,x80+, CVD subs 0+)
+
+All numbers are in big-endian and the image is interlaced with a
+resolution of 720x480 (ntsc) or 720x576 (pal)
+
+Data packets start with a 4 byte sequence number (Stream number(1),
+Packet number(1*), Subtitle number (2)) (*) this starts at 0, the last
+packet of a subtitle has the 7th bit set (the subtitle can be broken
+up into several packets when it is multiplexed into the mpeg stream)
+
+Subtitle Header (size in bytes):
+
+Packet length (2) (the assembled subtitle, with stripped sequence
+numbers) Option byte (1) normally set to 0x2e, bit 3 indicates that a
+field with the display-time of the subtitle is present.  what the
+other bits does is unknown.
+
+Time to display the sub (4) in 1/90000'th of a second (only present if
+bit 3 above is set)
+Xpos (2)
+Ypos (2)
+Width (2*)
+Height (2*)
+* should be even
+
+This only implies HOW LONG the subtitle will be shown, not when. That
+is given by the PTS in the PES header.
+
+Uknown Byte(1) 
+
+4 Palette Entries formated like:
+Y (1)
+U (1)
+V (1)
+Transparency(1)    (0 = transparent)
+
+Command (1) 
+>>6: 1 shift command, (cmd>>4)&3 is the direction (0=top, 1=left, 2 = right, 3 
+>>= bottom)
+
+Odd-field data offset (2)
+
+Then image data follows, and is formatted like this:
+2 bit codes are used so 01 means 1 pixel of color 1,
+10 means color 2 etc.
+
+Lines are padded to complete bytes, field 0 is padded to an even byte
+length and finally subtitles are padded to a multiple of 4 bytes
+(always atleast 1 zero byte at the end)
+
+Philips SVCD tools can create SVCD subtitles, but it only works under
+NT4, (and not that easy to find anymore.. dvd.da.ru, doom9.net or
+similar perhaps?), it can create good subtitled svcds and just open
+them in your favorite hex editor ^_^
+
+The subs you get from tools like "I-author" are not real SVCD
+subtitles, they are CVD sub and I don't know anything else about them
+except for that they look similar to dvd subs but the RLE encoding and
+command format is different.