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diff --git a/gst/mpeg2sub/Notes.txt b/gst/mpeg2sub/Notes.txt deleted file mode 100644 index a0e56e3c..00000000 --- a/gst/mpeg2sub/Notes.txt +++ /dev/null @@ -1,324 +0,0 @@ -
- DVD subtitles
- ---------------
-
-
- 0. Introduction
- 1. Basics
- 2. The data structure
- 3. Reading the control header
- 4. Decoding the graphics
- 5. What I do not know yet / What I need
- 6. Thanks
- 7. Changes
-
-
-
-
-
-The latest version of this document can be found here:
-http://www.via.ecp.fr/~sam/doc/dvd/
-
-
-
-
-
-0. Introduction
-
- One of the last things we missed in DVD decoding under my system was the
-decoding of subtitles. I found no information on the web or Usenet about them,
-apart from a few words on them being run-length encoded in the DVD FAQ.
-
- So we decided to reverse-engineer their format (it's completely legal in
-France, since we did it on interoperability purposes), and managed to get
-almost all of it.
-
-
-
-
-
-1. Basics
-
- DVD subtitles are hidden in private PS packets (0x000001ba), just like AC3
-streams are.
-
- Within the PS packet, there are PES packets, and like AC3, the header for the
-ones containing subtitles have a 0x000001bd header.
- As for AC3, where there's an ID like (0x80 + x), there's a subtitle ID equal
-to (0x20 + x), where x is the subtitle ID. Thus there seems to be only
-16 possible different subtitles on a DVD (my Taxi Driver copy has 16).
-
- I'll suppose you know how to extract AC3 from a DVD, and jump to the
-interesting part of this documentation. Anyway you're unlikely to have
-understood what I said without already being familiar with MPEG2.
-
-
-
-
-
-2. The data structure
-
-A subtitle packet, after its parts have been collected and appended, looks
-like this :
-
- +----------------------------------------------------------+
- | |
- | 0 2 size |
- | +----+------------------------+-----------------+ |
- | |size| data packet | control | |
- | +----+------------------------+-----------------+ |
- | |
- | a subtitle packet |
- | |
- +----------------------------------------------------------+
-
-size is a 2 bytes word, and data packet and control may have any size.
-
-
-Here is the structure of the data packet :
-
- +----------------------------------------------------------+
- | |
- | 2 4 S0+2 |
- | +----+------------------------------------------+ |
- | | S0 | data | |
- | +----+------------------------------------------+ |
- | |
- | the data packet |
- | |
- +----------------------------------------------------------+
-
-S0, the data packet size, is a 2 bytes word.
-
-
-Finally, here's the structure of the control packet :
-
- +----------------------------------------------------------+
- | |
- | S0+2 S0+4 S1 size |
- | +----+---------+---------+--+---------+--+---------+ |
- | | S1 |ctrl seq |ctrl seq |..|ctrl seq |ff| end seq | |
- | +----+---------+---------+--+---------+--+---------+ |
- | |
- | the control packet |
- | |
- +----------------------------------------------------------+
-
-To summarize :
-
- - S1, at offset S0+2, the position of the end sequence
- - several control sequences
- - the 'ff' byte
- - the end sequence
-
-
-
-
-
-3. Reading the control header
-
-The first thing to read is the control sequences. There are several
-types of them, and each type is determined by its first byte. As far
-as I know, each type has a fixed length.
-
- * type 0x01 : '01' - 1 byte
- it seems to be an empty control sequence.
-
- * type 0x03 : '03wxyz' - 3 bytes
- this one has the palette information ; it basically says 'encoded color 0
- is the wth color of the palette, encoded color 1 is the xth color, aso.
-
- * type 0x04 : '04wxyz' - 3 bytes
- I *think* this is the alpha channel information ; I only saw values of 0 or f
- for those nibbles, so I can't really be sure, but it seems plausable.
-
- * type 0x05 : '05xxxXXXyyyYYY' - 7 bytes
- the coordinates of the subtitle on the screen :
- xxx is the first column of the subtitle
- XXX is the last column of the subtitle
- yyy is the first line of the subtitle
- YYY is the last line of the subtitle
- thus the subtitle's size is (XXX-xxx+1) x (YYY-yyy+1)
-
- * type 0x06 : '06xxxxyyyy' - 5 bytes
- xxxx is the position of the first graphic line, and yyyy is the position of
- the second one (the graphics are interlaced, so it helps a lot :p)
-
-The end sequence has this structure:
-
- xxxx yyyy 02 ff (ff)
-
- it ends with 'ff' or 'ffff', to make the whole packet have an even length.
-
-FIXME: I absolutely don't know what xxxx is. I suppose it may be some date
-information since I found it nowhere else, but I can't be sure.
-
- yyyy is equal to S1 (see picture).
-
-
-Example of a control header :
-----
-0A 0C 01 03 02 31 04 0F F0 05 00 02 CF 00 22 3E 06 00 06 04 E9 FF 00 93 0A 0C 02 FF
-----
-Let's decode it. First of all, S1 = 0x0a0c.
-
-The control sequences are :
- 01
- Nothing to say about this one
- 03 02 31
- Color 0 is 0, color 1 is 2, color 2 is 3, and color 3 is 1.
- 04 0F F0
- Colors 0 and 3 are transparent, and colors 2 and 3 are opaque (not sure of this one)
- 05 00 02 CF 00 22 3E
- The first column is 0x000, the last one is 0x2cf, the first line is 0x002, and
- the last line is 0x23e. Thus the subtitle's size is 0x2d0 x 0x23d.
- 06 00 06 04 E9
- The first encoded image starts at offset 0x006, and the second one starts at 0x04e9.
-
-And the end sequence is :
- 00 93 0A 0C 02 FF
- Which means... well, not many things now. We can at least verify that S1 (0x0a0c) is
- there.
-
-
-
-
-
-4. Decoding the graphics
-
- The graphics are rather easy to decode (at least, when you know how to do it - it
- took us one whole week to figure out what the encoding was :p).
-
- The picture is interlaced, for instance for a 40 lines picture :
-
- line 0 ---------------#----------
- line 2 ------#-------------------
- ...
- line 38 ------------#-------------
- line 1 ------------------#-------
- line 3 --------#-----------------
- ...
- line 39 -------------#------------
-
- When decoding you should get:
-
- line 0 ---------------#----------
- line 1 ------------------#-------
- line 2 ------#-------------------
- line 3 --------#-----------------
- ...
- line 38 ------------#-------------
- line 39 -------------#------------
-
- Computers with weak processors could choose only to decode even lines
- in order to gain some time, for instance.
-
-
- The encoding is run-length encoded, with the following alphabet:
-
- 0xf
- 0xe
- 0xd
- 0xc
- 0xb
- 0xa
- 0x9
- 0x8
- 0x7
- 0x6
- 0x5
- 0x4
- 0x3-
- 0x2-
- 0x1-
- 0x0f-
- 0x0e-
- 0x0d-
- 0x0c-
- 0x0b-
- 0x0a-
- 0x09-
- 0x08-
- 0x07-
- 0x06-
- 0x05-
- 0x04-
- 0x03--
- 0x02--
- 0x01--
- 0x0000
-
- '-' stands for any other nibble. Once a sequence X of this alphabet has
- been read, the pixels can be displayed : (X >> 2) is the number of pixels
- to display, and (X & 0x3) is the color of the pixel.
-
- For instance, 0x23 means "8 pixels of color 3".
-
- "0000" has a special meaning : it's a carriage return. The decoder should
- do a carriage return when reaching the end of the line, or when encountering
- this "0000" sequence. When doing a carriage return, the parser should be
- reset to the next even position (it cannot be nibble-aligned at the start
- of a line).
-
- After a carriage return, the parser should read a line on the other
- interlaced picture, and swap like this after each carriage return.
-
- Perhaps I don't explain this very well, so you'd better have a look at
- the enclosed source.
-
-
-
-
-
-5. What I do not know yet / What I need
-
-I don't know what's in the end sequence yet.
-
-Also, I don't know exactly when to display subtitles, and when to remove them.
-
-I don't know if there are other types of control sequences (in my programs I consider
-0xff as a control sequence type, as well as 0x02. I don't know if it's correct or not,
-so please comment on this).
-
-I don't know what the "official" color palette is.
-
-I don't know how to handle transparency information.
-
-I don't know if this document is generic enough.
-
-So what I need is you :
-
- - if you can, patch this document or my programs to fix strange behaviour with your subtitles.
-
- - send me your subtitles (there's a program to extract them enclosed) ; the first 10 KB
- of subtitles in a VOB should be enough, but it would be cool if you sent me one subtitle
- file per language.
-
-
-
-
-
-6. Thanks
-
- Thanks to Michel Lespinasse <walken@via.ecp.fr> for his great help on understanding
-the RLE stuff, and for all the ideas he had.
-
- Thanks to mass (David Waite) and taaz (David I. Lehn) from irc at
-openprojects.net for sending me their subtitles.
-
-
-
-
-
-7. Changes
-
- 20000116: added the 'changes' section.
- 20000116: added David Waite's and David I. Lehn's name.
- 20000116: changed "x0" and "x1" to "S0" and "S1" to make it less confusing.
-
-
-
-
---
-Paris, January 16th 2000
-Samuel Hocevar <sam@via.ecp.fr>
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