222 lines
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11 KiB
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222 lines
No EOL
11 KiB
TeX
\documentclass{spec}
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\newcommand{\syntax}[1]{
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\subsubsection*{Syntax}
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\begin{tabbing}
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\hspace{2cm}\=\\[-16pt]
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#1
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\end{tabbing}
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}
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\newcommand{\secspec}[1]{Section:\>\texttt{#1}}
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\newcommand{\secspecs}[2]{Sections:\>\texttt{#1}, \texttt{#2}}
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\title{\LaTeX}
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\date{}
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\begin{document}
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\title{AS5 Subtitle Format Draft}
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\author{Rodrigo Braz Monteiro, Niels Martin Hansen, David Lamparter}
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\spectitle
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\section{Abstract}
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This document specifies the \emph{AS5 Subtitle Format}, developed jointly by the
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Aegisub\cite{Aegisub} and asa\cite{asa} teams in order to replace the old
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\emph{Sub Station Alpha}\cite{SSA} subtitle format and its extensions:
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\begin{itemize}
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\item Advanced Sub Station Alpha (ASS) implemented by Gabest in VSFilter\cite{VSFilter}
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\item Advanced Sub Station Alpha 2 (ASS2), also implemented by Gabest in VSFilter
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\item Advanced Sub Station Alpha 3 (ASS3) implemented by equinox in asa.
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\end{itemize}
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The goal is to create a flexible, easy to understand and powerful subtitle format
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that can be used in hardsubs or multiplexed into Matroska Video\cite{mkv} files as
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softsubs.
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AS5 has no official meaning. The "`A"' can stand for Aegisub, asa, ASS or Advanced,
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the "`S"' for Subtitles, and the 5 is a reference to the fact that it's a major
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improvement over SSA4 format (from which ASS, ASS2 and ASS3 derive). The full
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name of the format is "`AS5 Subtitle Format"'.
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\section{File Structure}
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\subsection{File Format}
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All AS5 files are \emph{REQUIRED} to comply with the three requirements below:
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\begin{itemize}
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\item Be encoded with one of \emph{UTF-8}\cite{UTF-8}, \emph{UTF-16 Big Endian}
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\cite{UTF-16} or \emph{UTF-16 Little Endian} Unicode Transformation Formats. UTF-8 is
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preffered.
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\item Not to have any character below Unicode code point U+20, except for U+09, U+0A, U+0D.
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That is, it must be a plain-text file.
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\item All lines must end with Windows line endings, that is, U+0D followed by U+0A.
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\end{itemize}
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The character set of a subtitle file can be autodetermined by its Byte-Order Mark or by
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the value of the first two bytes. See below.
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\subsection{File Structure}
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The file is divided in \emph{sections}, which are uniquely identified by a string inside
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square brackets, in a line of its own. From that point on, every next line is considered
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to be part of the last found section until another section is found. There is no end-of-section
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termination mark; they always end at the start of the next one or at the end of the file.
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\emph{Section names are case sensitive.}
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Each section is divided in lines, each line representing one command or definition. Empty
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lines \emph{MUST} be ignored. It is recommended that programs generating AS5 files insert
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a blank line at the end of each section to increase readability. There \emph{MUST} always
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be a blank line at the end of the file (as every line is required to end in a line break).
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Each line in a section takes the general form of \textit{Type: data1,data2,...,dataN}. An
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unknown \textit{Type} \emph{MUST} be ignored by a parser. It is recommended that subtitle
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editing programs keep such ignored lines in the file after re-saving it. Note that the space
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after the colon is \emph{mandatory}.
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There are two sections which are required, \emph{[AS5]} and \emph{[Events]}, the former being
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the equivalent of \emph{[Script Info]} in previous formats. If either of those sections is
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missing, the file is deemed invalid and \emph(MUST) be refused by the parser. Any other section
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can be ommitted from the file, and need not be implemented by all parsers. However, any unknown
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section \emph{MUST} be preserved in the file by a subtitle editing program when it re-saves a
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file with sections that it does not recognize. It can, however, be removed at the user's discretion.
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Finally, there is a special type of undefined group, \emph{[Private:PROGNAME]}, which
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\emph{MUST} be \emph{ENTIRELY} preserved by other programs when re-saving it. This is used to
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store program-specific data, for example, Aegisub would create a group called
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\emph{[Private:Aegisub]} to store its data inside. This type of group should be identified
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by the fact that it starts with \emph{"`[Private:"'}.
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\subsubsection{[AS5]}
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This must be the first section in every AS5 file. If the very first line of the file is not
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[AS5], the file \emph{MUST} be rejected by the parser as invalid. Note, however, that the first
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line is allowed to contain a Byte-Order Mark (BOM), which is the character U+FEFF encoded in
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the encoding used for the rest of the script\cite{Unicode BOM}. The first four bytes will therefore be:
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\begin{itemize}
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\item 0xEF 0xBB 0xBF 0x5B - UTF-8 (with BOM)
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\item 0x5B 0x41 0x53 0x53 - UTF-8 (without BOM)
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\item 0xFF 0xFE 0x5B 0x00 - UTF-16 LE (with BOM)
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\item 0x5B 0x00 0x41 0x00 - UTF-16 LE (without BOM)
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\item 0xFE 0xFF 0x00 0x5B - UTF-16 BE (with BOM)
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\item 0x00 0x5B 0x00 0x41 - UTF-16 BE (without BOM)
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\end{itemize}
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It is possible, therefore, to determine the encoding of the file by checking its first two bytes.
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This section is used to declare several script properties that affect its parsing and rendering.
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All properties are stored in the format \textit{Name: data}, with one property per line.
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This section \emph{MUST} always declare the following properties:
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\begin{itemize}
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\item ScriptType: Should always be set to \textit{AS5}, for this particular version of the specification.
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If this contains a value that the parser does not understand, it \emph{MUST} abort parsing.
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\item Resolution: Should contain the script resolution in \textit{WxH} format. For example, for a 640x480
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script, this should say \textit{"`Resolution: 640x480"'}. Note that this does not need to correspond to the
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video resolution, however, subtitles \emph{MUST} be rendered on such a coordinate space. That is, in a
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640x480 script, \textbackslash{pos(320,240)} always represents the center of the script, no matter the
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resolution of the video it's being drawn on. Also, in a 100x100 script, a radius 50 circle centered on
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the center will always take half of the height and half of the width of the video, even if that means
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being distorted if drawn on a 640x480 video.
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\end{itemize}
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Also, the following items are not required, but are recommended. They all have default values:
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\begin{itemize}
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\item Generator: The name of the program that generated this script, e.g. \textit{"`Generator: Aegisub"'}.
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Default value is empty. This should be ignored by the renderer, but might be useful for inter-editing-program
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interaction.
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\item Wrapping: The line wrapping style. This can be "`Manual"', in which case only \textbackslash{n} can
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break lines or "`Automatic"', in which the renderer chooses how to break them. The default is "`Automatic"'.
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Note that if this is set to manual, the line can NEVER be broken at anywhere other than forced line breaks,
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even if it means that the line will become unreadable because it goes outside the display area.
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\item Credits: Credits for the people who worked on this subtitle file. Should be ignored by the renderer.
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\item Title: The title of this script. Should be ignored by the renderer. Subtitling programs may opt to display
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this title to the user.
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\end{itemize}
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Although any other lines are allowed in this group, this is not encouraged, as they might conflict
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with future revisions of the format. Instead, they should be stored in \textit{[Private:PROGNAME]} groups,
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as mentioned above.
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\subsubsection{[Events]}
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The most important section, [Events], lists all the actual subtitle lines in the file. Each line is
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declared as \emph{"`Line: start,end,style,user,content"'} - the syntax has been radically simplified from
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previous incarnations of the format, and now consist of only five fields:
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\begin{itemize}
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\item Start: The start time of the line. See below for the timestamp format. A line is only displayed if
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the timestamp of the current frame is \emph{greater than or equal} to the start time. That is, start
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time is \emph{inclusive}.
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\item End: The end time of the line. It follows the same format as the start time. The line is only
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displayed if the timestamp of the current frame is \emph{lesser than} the end time. That is, end time is
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\emph{exclusive}. In particular, it means that a line whose start time is equal to its end time will
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never be displayed. If the end time is lesser than the start time, the renderer may issue a warning,
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but should render the remaining lines regardless of the issue.
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\item Style: The name of the default style used for this line. See the [Style] section below. Should be
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left blank if you want to use the the script's global default style. If an unknown style is specified,
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the renderer \emph{MUST} fallback to default, and might issue a warning.
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\item User: This field is used by the program to store program-specific data in each line. Renderers
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should ignore this. This should be left blank if it's not used.
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\item Content: The actual text of the line. This contains actual text and override tags. See the section
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on override tags for more information.
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\end{itemize}
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The timestamp format is h...h:mm:ss[.s...], that is, it begins with an integer of arbitrary length
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(up to a maximum of 4 digits) representing the number of hours, followed by two integers representing
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minutes, and a floating point number representing seconds. Localization is irrelevant: a period ("`."')
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is always used to separate the decimal point. This way, 0:21:42.5 and 0000:21:42.5000 are equivalent,
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and both represent 0 hours, 21 minutes, 42 seconds and 500 miliseconds.
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Spaces between each field \emph{MUST} be ignored by all parsers. Any spaces at the beginning of the
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content line should be stripped. A hard space or empty override block should be used if space at the
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start of a line is truly desirable. That is, the two following lines are identical:
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\begin{verbatim}
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Line: 0:12:31.57 , 0:12:34.22 , , , Hello world of {\b1}AS5{\b0}!
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Line: 0:12:31.57,0:12:34.22,,,Hello world of {\b1}AS5{\b0}!
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\end{verbatim}
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\addcontentsline{toc}{section}{References}
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\begin{thebibliography}{1}
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\bibitem{Aegisub} Rodrigo Braz Monteiro, Niels Martin Hansen, David Lamparter et al., Aegisub. Application, 2005-2007.\\
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\url{http://www.aegisub.net/}
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\bibitem{asa} David Lamparter, asa. Application, 2004-2007.\\
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\url{http://asa.diac24.net/}
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\bibitem{SSA} Kotus, Sub Station Alpha. Website, 1997-2003.\\
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\url{http://web.archive.org/web/*/http://www.eswat.demon.co.uk/substation.html}
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\bibitem{ASS} \#Anime-Fansubs, Advanced Sub Station Alpha.\\
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\url{http://www.anime-fansubs.org}\\
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\url{http://moodub.free.fr/video/ass-specs.doc}
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\bibitem{VSFilter} Gabest, VSFilter. Application, 2003-2007.\\
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\url{http://sourceforge.net/projects/guliverkli/}
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\bibitem{ASS3} David Lamparter, Advanced Sub Station Alpha 3. Website, 2007.\\
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\url{http://asa.diac24.net/ass3.pdf}
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\bibitem{mkv} The Matroska project.\\
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\url{http://www.matroska.org/}
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\bibitem{UTF-8} The Internet Society, RFC 3629, "`UTF-8, a transformation format of ISO 10646"'. Website, 2003.\\
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\url{http://tools.ietf.org/html/rfc3629}
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\bibitem{UTF-16} The Internet Society, RFC 2781, "`UTF-16, an encoding of ISO 10646"'. Website, 2000.\\
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\url{http://tools.ietf.org/html/rfc2781}
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\bibitem{Unicode BOM} Unicode, Inc, The Unicode Standard, Chapter 13. PDF, 1991-2000.\\
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\url{http://www.unicode.org/unicode/uni2book/ch13.pdf}
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\end{thebibliography}
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\end{document} |