\input texinfo @c -*- texinfo -*-
 
 @settitle Video Hook Documentation
 @titlepage
 @sp 7
 @center @titlefont{Video Hook Documentation}
 @sp 3
 @end titlepage
 
 
 @chapter Introduction
 

 @var{Please be aware that vhook is deprecated, and hence its development is
 frozen (bug fixes are still accepted).

 The substitute will be 'libavfilter', the result of our 'Video Filter API'
 Google Summer of Code project. You may monitor its progress by subscribing to
 the ffmpeg-soc mailing list at
 @url{http://lists.mplayerhq.hu/mailman/listinfo/ffmpeg-soc}.}

 
 The video hook functionality is designed (mostly) for live video. It allows
 the video to be modified or examined between the decoder and the encoder.
 
 Any number of hook modules can be placed inline, and they are run in the
 order that they were specified on the ffmpeg command line.
 

 The video hook modules are provided for use as a base for your own modules,
 and are described below.

 
 Modules are loaded using the -vhook option to ffmpeg. The value of this parameter

 is a space separated list of arguments. The first is the module name, and the rest

 are passed as arguments to the Configure function of the module.
 

 The modules are dynamic libraries: They have different suffixes (.so, .dll, .dylib)
 depending on your platform. And your platform dictates if they need to be
 somewhere in your PATH, or in your LD_LIBRARY_PATH. Otherwise you will need to
 specify the full path of the vhook file that you are using.
 

 @section null.c
 
 This does nothing. Actually it converts the input image to RGB24 and then converts
 it back again. This is meant as a sample that you can use to test your setup.
 
 @section fish.c
 
 This implements a 'fish detector'. Essentially it converts the image into HSV
 space and tests whether more than a certain percentage of the pixels fall into
 a specific HSV cuboid. If so, then the image is saved into a file for processing
 by other bits of code.
 
 Why use HSV? It turns out that HSV cuboids represent a more compact range of
 colors than would an RGB cuboid.
 
 @section imlib2.c
 

 This module implements a text overlay for a video image. Currently it
 supports a fixed overlay or reading the text from a file. The string

 is passed through strftime() so that it is easy to imprint the date and

 time onto the image.
 

 This module depends on the external library imlib2, available on
 Sourceforge, among other places, if it is not already installed on
 your system.
 

 You may also overlay an image (even semi-transparent) like TV stations do.
 You may move either the text or the image around your video to create
 scrolling credits, for example.
 

 The font file used is looked for in a FONTPATH environment variable, and
 prepended to the point size as a command line option and can be specified
 with the full path to the font file, as in:
 @example
 -F /usr/X11R6/lib/X11/fonts/TTF/VeraBd.ttf/20
 @end example
 where 20 is the point size.

 You can specify the filename to read RGB color names from. If it is not

 specified, these defaults are used: @file{/usr/share/X11/rgb.txt} and
 @file{/usr/lib/X11/rgb.txt}
 

 Options:
 @multitable @columnfractions .2 .8

 @item @option{-C <rgb.txt>}   @tab The filename to read RGB color names from

 @item @option{-c <color>}     @tab The color of the text
 @item @option{-F <fontname>}  @tab The font face and size
 @item @option{-t <text>}      @tab The text
 @item @option{-f <filename>}  @tab The filename to read text from

 @item @option{-x <expression>}@tab x coordinate of text or image
 @item @option{-y <expression>}@tab y coordinate of text or image

 @item @option{-i <filename>}  @tab The filename to read a image from

 @item @option{-R <expression>}@tab Value for R color
 @item @option{-G <expression>}@tab Value for G color
 @item @option{-B <expression>}@tab Value for B color
 @item @option{-A <expression>}@tab Value for Alpha channel

 @end multitable
 

 Expressions are functions of these variables:

 @multitable @columnfractions .2 .8
 @item @var{N} @tab frame number (starting at zero)
 @item @var{H} @tab frame height
 @item @var{W} @tab frame width
 @item @var{h} @tab image height
 @item @var{w} @tab image width
 @item @var{X} @tab previous x coordinate of text or image
 @item @var{Y} @tab previous y coordinate of text or image
 @end multitable
 
 You may also use the constants @var{PI}, @var{E}, and the math functions available at the
 FFmpeg formula evaluator at (@url{ffmpeg-doc.html#SEC13}), except @var{bits2qp(bits)}
 and @var{qp2bits(qp)}.
 
 Usage examples:
 
 @example
    # Remember to set the path to your fonts
    FONTPATH="/cygdrive/c/WINDOWS/Fonts/"
    FONTPATH="$FONTPATH:/usr/share/imlib2/data/fonts/"
    FONTPATH="$FONTPATH:/usr/X11R6/lib/X11/fonts/TTF/"
    export FONTPATH
 
    # Bulb dancing in a Lissajous pattern
    ffmpeg -i input.avi -vhook \
      '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' \
      -acodec copy -sameq output.avi
 
    # Text scrolling
    ffmpeg -i input.avi -vhook \
      'vhook/imlib2.dll -c red -F Vera.ttf/20 -x 150+0.5*N -y 70+0.25*N -t Hello' \
      -acodec copy -sameq output.avi

 
    # Date and time stamp, security-camera style:
    ffmpeg -r 29.97 -s 320x256 -f video4linux -i /dev/video0 \
      -vhook 'vhook/imlib2.so -x 0 -y 0 -i black-260x20.png' \
      -vhook 'vhook/imlib2.so -c white -F VeraBd.ttf/12 -x 0 -y 0 -t %A-%D-%T' \
      output.avi
 
      In this example the video is captured from the first video capture card as a
      320x256 AVI, and a black 260 by 20 pixel PNG image is placed in the upper
      left corner, with the day, date and time overlaid on it in Vera Bold 12
      point font. A simple black PNG file 260 pixels wide and 20 pixels tall
      was created in the GIMP for this purpose.
 
    # Scrolling credits from a text file
    ffmpeg -i input.avi -vhook \
      'vhook/imlib2.so -c white -F VeraBd.ttf/16 -x 100 -y -1.0*N -f credits.txt' \
      -sameq output.avi
 
      In this example, the text is stored in a file, and is positioned 100
      pixels from the left hand edge of the video. The text is scrolled from the
      bottom up. Making the y factor positive will scroll from the top down.
      Increasing the magnitude of the y factor makes the text scroll faster,
      decreasing it makes it scroll slower. Hint: Blank lines containing only
      a newline are treated as end-of-file. To create blank lines, use lines
      that consist of space characters only.
 

    # Scrolling credits with custom color from a text file
    ffmpeg -i input.avi -vhook \
      'vhook/imlib2.so -C rgb.txt -c CustomColor1 -F VeraBd.ttf/16 -x 100 -y -1.0*N -f credits.txt' \
      -sameq output.avi
 

      This example does the same as the one above, but specifies an rgb.txt file

      to be used, which has a custom-made color in it.

    # Variable colors
    ffmpeg -i input.avi -vhook \
      'vhook/imlib2.so -t Hello -R abs(255*sin(N/47*PI)) -G abs(255*sin(N/47*PI)) -B abs(255*sin(N/47*PI))' \
      -sameq output.avi
 
      In this example, the color for the text goes up and down from black to
      white.
 

    # Text fade-out
    ffmpeg -i input.avi -vhook \
      'vhook/imlib2.so -t Hello -A max(0,255-exp(N/47))' \
      -sameq output.avi
 
      In this example, the text fades out in about 10 seconds for a 25 fps input
      video file.
 

    # scrolling credits from a graphics file
    ffmpeg -sameq -i input.avi \
      -vhook 'vhook/imlib2.so -x 0 -y -1.0*N -i credits.png' output.avi
 
      In this example, a transparent PNG file the same width as the video
      (e.g. 320 pixels), but very long, (e.g. 3000 pixels), was created, and
      text, graphics, brushstrokes, etc, were added to the image. The image
      is then scrolled up, from the bottom of the frame.
 

 @end example

 @section ppm.c
 
 It's basically a launch point for a PPM pipe, so you can use any
 executable (or script) which consumes a PPM on stdin and produces a PPM

 on stdout (and flushes each frame). The Netpbm utilities are a series of
 such programs.
 
 A list of them is here:
 
 @url{http://netpbm.sourceforge.net/doc/directory.html}

 
 Usage example:
 
 @example
 ffmpeg -i input -vhook "/path/to/ppm.so some-ppm-filter args" output
 @end example

 @section drawtext.c
 
 This module implements a text overlay for a video image. Currently it
 supports a fixed overlay or reading the text from a file. The string
 is passed through strftime() so that it is easy to imprint the date and
 time onto the image.
 
 Features:
 @itemize @minus
 @item TrueType, Type1 and others via the FreeType2 library
 @item Font kerning (better output)
 @item Line Wrap (put the text that doesn't fit one line on the next line)
 @item Background box (currently in development)
 @item Outline
 @end itemize
 
 Options:
 @multitable @columnfractions .2 .8
 @item @option{-c <color>}          @tab Foreground color of the text ('internet' way) <#RRGGBB> [default #FFFFFF]
 @item @option{-C <color>}          @tab Background color of the text ('internet' way) <#RRGGBB> [default #000000]
 @item @option{-f <font-filename>}  @tab font file to use
 @item @option{-t <text>}           @tab text to display
 @item @option{-T <filename>}       @tab file to read text from
 @item @option{-x <pos>}            @tab x coordinate of the start of the text
 @item @option{-y <pos>}            @tab y coordinate of the start of the text
 @end multitable
 
 Text fonts are being looked for in a FONTPATH environment variable.
 If the FONTPATH environment variable is not available, or is not checked by
 your target (i.e. Cygwin), then specify the full path to the font file as in:
 @example
 -f /usr/X11R6/lib/X11/fonts/TTF/VeraBd.ttf
 @end example
 
 Usage Example:
 @example
    # Remember to set the path to your fonts
    FONTPATH="/cygdrive/c/WINDOWS/Fonts/"
    FONTPATH="$FONTPATH:/usr/share/imlib2/data/fonts/"
    FONTPATH="$FONTPATH:/usr/X11R6/lib/X11/fonts/TTF/"
    export FONTPATH
 
    # Time and date display
    ffmpeg -f video4linux2 -i /dev/video0 \
    -vhook 'vhook/drawtext.so -f VeraBd.ttf -t %A-%D-%T' movie.mpg
 
      This example grabs video from the first capture card and outputs it to an
      MPEG video, and places "Weekday-dd/mm/yy-hh:mm:ss" at the top left of the
      frame, updated every second, using the Vera Bold TrueType Font, which
      should exist in: /usr/X11R6/lib/X11/fonts/TTF/
 @end example
 
 Check the man page for strftime() for all the various ways you can format
 the date and time.
 
 @section watermark.c
 
 Command Line options:
 @multitable @columnfractions .2 .8
 @item @option{-m [0|1]}            @tab Mode (default: 0, see below)
 @item @option{-t 000000 - FFFFFF}  @tab Threshold, six digit hex number
 @item @option{-f <filename>}       @tab Watermark image filename, must be specified!
 @end multitable
 
 MODE 0:
  The watermark picture works like this (assuming color intensities 0..0xFF):
  Per color do this:
  If mask color is 0x80, no change to the original frame.
  If mask color is < 0x80 the absolute difference is subtracted from the
  frame. If result < 0, result = 0.
  If mask color is > 0x80 the absolute difference is added to the
  frame. If result > 0xFF, result = 0xFF.
 
  You can override the 0x80 level with the -t flag. E.g. if threshold is
  000000 the color value of watermark is added to the destination.
 
  This way a mask that is visible both in light and dark pictures can be made
  (e.g. by using a picture generated by the Gimp and the bump map tool).
 
  An example watermark file is at:
  @url{http://engene.se/ffmpeg_watermark.gif}
 
 MODE 1:
  Per color do this:
  If mask color > threshold color then the watermark pixel is used.
 
 Example usage:
 @example
    ffmpeg -i infile -vhook '/path/watermark.so -f wm.gif' -an out.mov
    ffmpeg -i infile -vhook '/path/watermark.so -f wm.gif -m 1 -t 222222' -an out.mov
 @end example
 

 @bye