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\input texinfo @c -*- texinfo -*-
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@settitle Video Hook Documentation
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@titlepage
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@sp 7
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@center @titlefont{Video Hook Documentation}
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@sp 3
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@end titlepage
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@chapter Introduction
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The video hook functionality is designed (mostly) for live video. It allows
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the video to be modified or examined between the decoder and the encoder.
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Any number of hook modules can be placed inline, and they are run in the
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order that they were specified on the ffmpeg command line.
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The video hook modules are provided for use as a base for your own modules,
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and are described below.
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Modules are loaded using the -vhook option to ffmpeg. The value of this parameter
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is a space separated list of arguments. The first is the module name, and the rest
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are passed as arguments to the Configure function of the module.
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The modules are dynamic libraries: They have different suffixes (.so, .dll, .dylib)
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depending on your platform. And your platform dictates if they need to be
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somewhere in your PATH, or in your LD_LIBRARY_PATH. Otherwise you will need to
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specify the full path of the vhook file that you are using.
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@section null.c
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This does nothing. Actually it converts the input image to RGB24 and then converts
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it back again. This is meant as a sample that you can use to test your setup.
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@section fish.c
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This implements a 'fish detector'. Essentially it converts the image into HSV
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space and tests whether more than a certain percentage of the pixels fall into
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a specific HSV cuboid. If so, then the image is saved into a file for processing
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by other bits of code.
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Why use HSV? It turns out that HSV cuboids represent a more compact range of
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colors than would an RGB cuboid.
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@section imlib2.c
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This module implements a text overlay for a video image. Currently it
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supports a fixed overlay or reading the text from a file. The string
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is passed through strftime() so that it is easy to imprint the date and
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time onto the image.
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This module depends on the external library imlib2, available on
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Sourceforge, among other places, if it is not already installed on
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your system.
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You may also overlay an image (even semi-transparent) like TV stations do.
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You may move either the text or the image around your video to create
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scrolling credits, for example.
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The font file used is looked for in a FONTPATH environment variable, and
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prepended to the point size as a command line option and can be specified
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with the full path to the font file, as in:
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@example
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-F /usr/X11R6/lib/X11/fonts/TTF/VeraBd.ttf/20
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@end example
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where 20 is the point size.
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Options:
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@multitable @columnfractions .2 .8
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@item @option{-c <color>}     @tab The color of the text
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@item @option{-F <fontname>}  @tab The font face and size
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@item @option{-t <text>}      @tab The text
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@item @option{-f <filename>}  @tab The filename to read text from
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@item @option{-x <expresion>} @tab x coordinate of text or image
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@item @option{-y <expresion>} @tab y coordinate of text or image
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@item @option{-i <filename>}  @tab The filename to read a image from
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@end multitable
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Expresions are functions of these variables:
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@multitable @columnfractions .2 .8
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@item @var{N} @tab frame number (starting at zero)
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@item @var{H} @tab frame height
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@item @var{W} @tab frame width
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@item @var{h} @tab image height
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@item @var{w} @tab image width
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@item @var{X} @tab previous x coordinate of text or image
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@item @var{Y} @tab previous y coordinate of text or image
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@end multitable
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You may also use the constants @var{PI}, @var{E}, and the math functions available at the
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FFmpeg formula evaluator at (@url{ffmpeg-doc.html#SEC13}), except @var{bits2qp(bits)}
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and @var{qp2bits(qp)}.
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Usage examples:
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@example
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   # Remember to set the path to your fonts
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   FONTPATH="/cygdrive/c/WINDOWS/Fonts/"
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   FONTPATH="$FONTPATH:/usr/share/imlib2/data/fonts/"
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   FONTPATH="$FONTPATH:/usr/X11R6/lib/X11/fonts/TTF/"
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   export FONTPATH
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   # Bulb dancing in a Lissajous pattern
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   ffmpeg -i input.avi -vhook \
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     'vhook/imlib2.dll -x W*(0.5+0.25*sin(N/47*PI))-w/2 -y H*(0.5+0.50*cos(N/97*PI))-h/2 -i /usr/share/imlib2/data/images/bulb.png' \
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     -acodec copy -sameq output.avi
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   # Text scrolling
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   ffmpeg -i input.avi -vhook \
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     'vhook/imlib2.dll -c red -F Vera.ttf/20 -x 150+0.5*N -y 70+0.25*N -t Hello' \
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     -acodec copy -sameq output.avi
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   # Date and time stamp, security-camera style:
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   ffmpeg -r 29.97 -s 320x256 -f video4linux -i /dev/video0 \
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     -vhook 'vhook/imlib2.so -x 0 -y 0 -i black-260x20.png' \
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     -vhook 'vhook/imlib2.so -c white -F VeraBd.ttf/12 -x 0 -y 0 -t %A-%D-%T' \
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     output.avi
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     In this example the video is captured from the first video capture card as a
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     320x256 AVI, and a black 260 by 20 pixel PNG image is placed in the upper
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     left corner, with the day, date and time overlaid on it in Vera Bold 12
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     point font. A simple black PNG file 260 pixels wide and 20 pixels tall
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     was created in the GIMP for this purpose.
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   # Scrolling credits from a text file
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   ffmpeg -i input.avi -vhook \
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     'vhook/imlib2.so -c white -F VeraBd.ttf/16 -x 100 -y -1.0*N -f credits.txt' \
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     -sameq output.avi
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     In this example, the text is stored in a file, and is positioned 100
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     pixels from the left hand edge of the video. The text is scrolled from the
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     bottom up. Making the y factor positive will scroll from the top down.
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     Increasing the magnitude of the y factor makes the text scroll faster,
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     decreasing it makes it scroll slower. Hint: Blank lines containing only
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     a newline are treated as end-of-file. To create blank lines, use lines
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     that consist of space characters only.
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   # scrolling credits from a graphics file
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   ffmpeg -sameq -i input.avi \
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     -vhook 'vhook/imlib2.so -x 0 -y -1.0*N -i credits.png' output.avi
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     In this example, a transparent PNG file the same width as the video
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     (e.g. 320 pixels), but very long, (e.g. 3000 pixels), was created, and
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     text, graphics, brushstrokes, etc, were added to the image. The image
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     is then scrolled up, from the bottom of the frame.
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@end example
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@section ppm.c
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It's basically a launch point for a PPM pipe, so you can use any
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executable (or script) which consumes a PPM on stdin and produces a PPM
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on stdout (and flushes each frame). The Netpbm utilities are a series of
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such programs.
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A list of them is here:
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@url{http://netpbm.sourceforge.net/doc/directory.html}
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Usage example:
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@example
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ffmpeg -i input -vhook "/path/to/ppm.so some-ppm-filter args" output
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@end example
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@section drawtext.c
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This module implements a text overlay for a video image. Currently it
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supports a fixed overlay or reading the text from a file. The string
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is passed through strftime() so that it is easy to imprint the date and
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time onto the image.
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Features:
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@itemize @minus
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@item TrueType, Type1 and others via the FreeType2 library
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@item Font kerning (better output)
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@item Line Wrap (put the text that doesn't fit one line on the next line)
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@item Background box (currently in development)
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@item Outline
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@end itemize
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Options:
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@multitable @columnfractions .2 .8
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@item @option{-c <color>}          @tab Foreground color of the text ('internet' way) <#RRGGBB> [default #FFFFFF]
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@item @option{-C <color>}          @tab Background color of the text ('internet' way) <#RRGGBB> [default #000000]
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@item @option{-f <font-filename>}  @tab font file to use
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@item @option{-t <text>}           @tab text to display
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@item @option{-T <filename>}       @tab file to read text from
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@item @option{-x <pos>}            @tab x coordinate of the start of the text
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@item @option{-y <pos>}            @tab y coordinate of the start of the text
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@end multitable
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Text fonts are being looked for in a FONTPATH environment variable.
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If the FONTPATH environment variable is not available, or is not checked by
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your target (i.e. Cygwin), then specify the full path to the font file as in:
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@example
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-f /usr/X11R6/lib/X11/fonts/TTF/VeraBd.ttf
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@end example
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Usage Example:
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@example
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   # Remember to set the path to your fonts
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   FONTPATH="/cygdrive/c/WINDOWS/Fonts/"
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   FONTPATH="$FONTPATH:/usr/share/imlib2/data/fonts/"
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   FONTPATH="$FONTPATH:/usr/X11R6/lib/X11/fonts/TTF/"
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   export FONTPATH
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   # Time and date display
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   ffmpeg -f video4linux2 -i /dev/video0 \
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   -vhook 'vhook/drawtext.so -f VeraBd.ttf -t %A-%D-%T' movie.mpg
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     This example grabs video from the first capture card and outputs it to an
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     MPEG video, and places "Weekday-dd/mm/yy-hh:mm:ss" at the top left of the
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     frame, updated every second, using the Vera Bold TrueType Font, which
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     should exist in: /usr/X11R6/lib/X11/fonts/TTF/
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@end example
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Check the man page for strftime() for all the various ways you can format
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the date and time.
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@section watermark.c
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Command Line options:
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@multitable @columnfractions .2 .8
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@item @option{-m [0|1]}            @tab Mode (default: 0, see below)
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@item @option{-t 000000 - FFFFFF}  @tab Threshold, six digit hex number
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@item @option{-f <filename>}       @tab Watermark image filename, must be specified!
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@end multitable
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MODE 0:
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 The watermark picture works like this (assuming color intensities 0..0xFF):
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 Per color do this:
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 If mask color is 0x80, no change to the original frame.
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 If mask color is < 0x80 the absolute difference is subtracted from the
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 frame. If result < 0, result = 0.
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 If mask color is > 0x80 the absolute difference is added to the
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 frame. If result > 0xFF, result = 0xFF.
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 You can override the 0x80 level with the -t flag. E.g. if threshold is
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 000000 the color value of watermark is added to the destination.
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 This way a mask that is visible both in light and dark pictures can be made
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 (e.g. by using a picture generated by the Gimp and the bump map tool).
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 An example watermark file is at:
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 @url{http://engene.se/ffmpeg_watermark.gif}
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MODE 1:
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 Per color do this:
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 If mask color > threshold color then the watermark pixel is used.
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Example usage:
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@example
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   ffmpeg -i infile -vhook '/path/watermark.so -f wm.gif' -an out.mov
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   ffmpeg -i infile -vhook '/path/watermark.so -f wm.gif -m 1 -t 222222' -an out.mov
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@end example
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@bye