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231 lines
4.8 KiB
Plaintext
231 lines
4.8 KiB
Plaintext
@chapter Syntax
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@c man begin SYNTAX
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This section documents the syntax and formats employed by the FFmpeg
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libraries and tools.
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@anchor{quoting_and_escaping}
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@section Quoting and escaping
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FFmpeg adopts the following quoting and escaping mechanism, unless
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explicitly specified. The following rules are applied:
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@itemize
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@item
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@code{'} and @code{\} are special characters (respectively used for
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quoting and escaping). In addition to them, there might be other
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special characters depending on the specific syntax where the escaping
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and quoting are employed.
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@item
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A special character is escaped by prefixing it with a '\'.
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@item
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All characters enclosed between '' are included literally in the
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parsed string. The quote character @code{'} itself cannot be quoted,
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so you may need to close the quote and escape it.
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@item
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Leading and trailing whitespaces, unless escaped or quoted, are
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removed from the parsed string.
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@end itemize
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Note that you may need to add a second level of escaping when using
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the command line or a script, which depends on the syntax of the
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adopted shell language.
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The function @code{av_get_token} defined in
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@file{libavutil/avstring.h} can be used to parse a token quoted or
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escaped according to the rules defined above.
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The tool @file{tools/ffescape} in the FFmpeg source tree can be used
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to automatically quote or escape a string in a script.
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@subsection Examples
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@itemize
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@item
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Escape the string @code{Crime d'Amour} containing the @code{'} special
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character:
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@example
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Crime d\'Amour
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@end example
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@item
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The string above contains a quote, so the @code{'} needs to be escaped
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when quoting it:
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@example
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'Crime d'\''Amour'
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@end example
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@item
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Include leading or trailing whitespaces using quoting:
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@example
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' this string starts and ends with whitespaces '
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@end example
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@item
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Escaping and quoting can be mixed together:
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@example
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' The string '\'string\'' is a string '
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@end example
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@item
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To include a literal @code{\} you can use either escaping or quoting:
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@example
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'c:\foo' can be written as c:\\foo
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@end example
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@end itemize
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@anchor{date syntax}
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@section Date
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The accepted syntax is:
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@example
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[(YYYY-MM-DD|YYYYMMDD)[T|t| ]]((HH:MM:SS[.m...]]])|(HHMMSS[.m...]]]))[Z]
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now
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@end example
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If the value is "now" it takes the current time.
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Time is local time unless Z is appended, in which case it is
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interpreted as UTC.
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If the year-month-day part is not specified it takes the current
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year-month-day.
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@anchor{time duration syntax}
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@section Time duration
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The accepted syntax is:
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@example
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[-]HH:MM:SS[.m...]
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[-]S+[.m...]
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@end example
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@var{HH} expresses the number of hours, @var{MM} the number a of minutes
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and @var{SS} the number of seconds.
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@anchor{video size syntax}
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@section Video size
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Specify the size of the sourced video, it may be a string of the form
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@var{width}x@var{height}, or the name of a size abbreviation.
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The following abbreviations are recognized:
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@table @samp
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@item sqcif
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128x96
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@item qcif
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176x144
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@item cif
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352x288
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@item 4cif
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704x576
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@item 16cif
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1408x1152
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@item qqvga
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160x120
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@item qvga
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320x240
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@item vga
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640x480
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@item svga
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800x600
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@item xga
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1024x768
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@item uxga
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1600x1200
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@item qxga
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2048x1536
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@item sxga
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1280x1024
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@item qsxga
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2560x2048
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@item hsxga
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5120x4096
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@item wvga
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852x480
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@item wxga
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1366x768
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@item wsxga
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1600x1024
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@item wuxga
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1920x1200
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@item woxga
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2560x1600
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@item wqsxga
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3200x2048
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@item wquxga
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3840x2400
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@item whsxga
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6400x4096
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@item whuxga
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7680x4800
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@item cga
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320x200
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@item ega
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640x350
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@item hd480
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852x480
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@item hd720
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1280x720
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@item hd1080
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1920x1080
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@end table
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@anchor{video rate syntax}
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@section Video rate
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Specify the frame rate of a video, expressed as the number of frames
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generated per second. It has to be a string in the format
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@var{frame_rate_num}/@var{frame_rate_den}, an integer number, a float
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number or a valid video frame rate abbreviation.
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The following abbreviations are recognized:
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@table @samp
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@item ntsc
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30000/1001
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@item pal
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25/1
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@item qntsc
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30000/1
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@item qpal
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25/1
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@item sntsc
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30000/1
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@item spal
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25/1
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@item film
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24/1
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@item ntsc-film
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24000/1
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@end table
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@anchor{ratio syntax}
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@section Ratio
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A ratio can be expressed as an expression, or in the form
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@var{numerator}:@var{denominator}.
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Note that a ratio with infinite (1/0) or negative value is
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considered valid, so you should check on the returned value if you
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want to exclude those values.
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The undefined value can be expressed using the "0:0" string.
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@anchor{color syntax}
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@section Color
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It can be the name of a color (case insensitive match) or a
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[0x|#]RRGGBB[AA] sequence, possibly followed by "@@" and a string
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representing the alpha component.
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The alpha component may be a string composed by "0x" followed by an
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hexadecimal number or a decimal number between 0.0 and 1.0, which
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represents the opacity value (0x00/0.0 means completely transparent,
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0xff/1.0 completely opaque).
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If the alpha component is not specified then 0xff is assumed.
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The string "random" will result in a random color.
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@c man end SYNTAX
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