path: root/doc/syntax.texi

@chapter Syntax
@c man begin SYNTAX

This section documents the syntax and formats employed by the FFmpeg
libraries and tools.

@anchor{quoting_and_escaping}
@section Quoting and escaping

FFmpeg adopts the following quoting and escaping mechanism, unless
explicitly specified. The following rules are applied:

@itemize
@item
@code{'} and @code{\} are special characters (respectively used for
quoting and escaping). In addition to them, there might be other
special characters depending on the specific syntax where the escaping
and quoting are employed.

@item
A special character is escaped by prefixing it with a '\'.

@item
All characters enclosed between '' are included literally in the
parsed string. The quote character @code{'} itself cannot be quoted,
so you may need to close the quote and escape it.

@item
Leading and trailing whitespaces, unless escaped or quoted, are
removed from the parsed string.
@end itemize

Note that you may need to add a second level of escaping when using
the command line or a script, which depends on the syntax of the
adopted shell language.

The function @code{av_get_token} defined in
@file{libavutil/avstring.h} can be used to parse a token quoted or
escaped according to the rules defined above.

The tool @file{tools/ffescape} in the FFmpeg source tree can be used
to automatically quote or escape a string in a script.

@subsection Examples

@itemize
@item
Escape the string @code{Crime d'Amour} containing the @code{'} special
character:
@example
Crime d\'Amour
@end example

@item
The string above contains a quote, so the @code{'} needs to be escaped
when quoting it:
@example
'Crime d'\''Amour'
@end example

@item
Include leading or trailing whitespaces using quoting:
@example
'  this string starts and ends with whitespaces  '
@end example

@item
Escaping and quoting can be mixed together:
@example
' The string '\'string\'' is a string '
@end example

@item
To include a literal @code{\} you can use either escaping or quoting:
@example
'c:\foo' can be written as c:\\foo
@end example
@end itemize

@anchor{date syntax}
@section Date

The accepted syntax is:
@example
[(YYYY-MM-DD|YYYYMMDD)[T|t| ]]((HH:MM:SS[.m...]]])|(HHMMSS[.m...]]]))[Z]
now
@end example

If the value is "now" it takes the current time.

Time is local time unless Z is appended, in which case it is
interpreted as UTC.
If the year-month-day part is not specified it takes the current
year-month-day.

@anchor{time duration syntax}
@section Time duration

The accepted syntax is:
@example
[-]HH:MM:SS[.m...]
[-]S+[.m...]
@end example

@var{HH} expresses the number of hours, @var{MM} the number a of minutes
and @var{SS} the number of seconds.

@anchor{video size syntax}
@section Video size
Specify the size of the sourced video, it may be a string of the form
@var{width}x@var{height}, or the name of a size abbreviation.

The following abbreviations are recognized:
@table @samp
@item ntsc
720x480
@item pal
720x576
@item qntsc
352x240
@item qpal
352x288
@item sntsc
640x480
@item spal
768x576
@item film
352x240
@item ntsc-film
352x240
@item sqcif
128x96
@item qcif
176x144
@item cif
352x288
@item 4cif
704x576
@item 16cif
1408x1152
@item qqvga
160x120
@item qvga
320x240
@item vga
640x480
@item svga
800x600
@item xga
1024x768
@item uxga
1600x1200
@item qxga
2048x1536
@item sxga
1280x1024
@item qsxga
2560x2048
@item hsxga
5120x4096
@item wvga
852x480
@item wxga
1366x768
@item wsxga
1600x1024
@item wuxga
1920x1200
@item woxga
2560x1600
@item wqsxga
3200x2048
@item wquxga
3840x2400
@item whsxga
6400x4096
@item whuxga
7680x4800
@item cga
320x200
@item ega
640x350
@item hd480
852x480
@item hd720
1280x720
@item hd1080
1920x1080
@item 2k
2048x1080
@item 2kflat
1998x1080
@item 2kscope
2048x858
@item 4k
4096x2160
@item 4kflat
3996x2160
@item 4kscope
4096x1716
@end table

@anchor{video rate syntax}
@section Video rate

Specify the frame rate of a video, expressed as the number of frames
generated per second. It has to be a string in the format
@var{frame_rate_num}/@var{frame_rate_den}, an integer number, a float
number or a valid video frame rate abbreviation.

The following abbreviations are recognized:
@table @samp
@item ntsc
30000/1001
@item pal
25/1
@item qntsc
30000/1001
@item qpal
25/1
@item sntsc
30000/1001
@item spal
25/1
@item film
24/1
@item ntsc-film
24000/1001
@end table

@anchor{ratio syntax}
@section Ratio

A ratio can be expressed as an expression, or in the form
@var{numerator}:@var{denominator}.

Note that a ratio with infinite (1/0) or negative value is
considered valid, so you should check on the returned value if you
want to exclude those values.

The undefined value can be expressed using the "0:0" string.

@anchor{color syntax}
@section Color

It can be the name of a color (case insensitive match) or a
[0x|#]RRGGBB[AA] sequence, possibly followed by "@@" and a string
representing the alpha component.

The alpha component may be a string composed by "0x" followed by an
hexadecimal number or a decimal number between 0.0 and 1.0, which
represents the opacity value (0x00/0.0 means completely transparent,
0xff/1.0 completely opaque).
If the alpha component is not specified then 0xff is assumed.

The string "random" will result in a random color.

@c man end SYNTAX