x11grab: add follow_mouse AVOption.

-follow_mouse centered|PIXELS
  move grabbing region to where mouse pointer at the center; or
  only move when pointer reaches within PIXELS to the edge.

Signed-off-by: Yu-Jie Lin <livibetter@gmail.com>
Signed-off-by: Anton Khirnov <anton@khirnov.net>

2 files changed, 36 insertions, 3 deletions

diff --git a/doc/ffmpeg.texi b/doc/ffmpeg.texi
index 4dca5d8991..8d3968dbf2 100644
--- a/doc/ffmpeg.texi
+++ b/doc/ffmpeg.texi
@@ -900,8 +900,21 @@ the DISPLAY environment variable.
 ffmpeg -f x11grab -s cif -r 25 -i :0.0+10,20 /tmp/out.mpg
 @end example
 
-0.0 is display.screen number of your X11 server, same as the DISPLAY environment
-variable. 10 is the x-offset and 20 the y-offset for the grabbing.
+10 is the x-offset and 20 the y-offset for the grabbing.
+
+@example
+ffmpeg -f x11grab -follow_mouse centered -s cif -r 25 -i :0.0 /tmp/out.mpg
+@end example
+
+The grabbing region follows the mouse pointer, which stays at the center of
+region.
+
+@example
+ffmpeg -f x11grab -follow_mouse 100 -s cif -r 25 -i :0.0 /tmp/out.mpg
+@end example
+
+Only follows when mouse pointer reaches within 100 pixels to the edge of
+region.
 
 @section Video and Audio file format conversion
 
diff --git a/doc/indevs.texi b/doc/indevs.texi
index c5e04b029e..aa001cdb63 100644
--- a/doc/indevs.texi
+++ b/doc/indevs.texi
@@ -248,7 +248,27 @@ For example to grab from @file{:0.0} using @file{ffmpeg}:
 ffmpeg -f x11grab -r 25 -s cif -i :0.0 out.mpg
 
 # Grab at position 10,20.
-ffmpeg -f x11grab -25 -s cif -i :0.0+10,20 out.mpg
+ffmpeg -f x11grab -r 25 -s cif -i :0.0+10,20 out.mpg
+@end example
+
+@subsection @var{follow_mouse} AVOption
+
+The syntax is:
+@example
+-follow_mouse centered|@var{PIXELS}
+@end example
+
+When it is specified with "centered", the grabbing region follows the mouse
+pointer and keeps the pointer at the center of region; otherwise, the region
+follows only when the mouse pointer reaches within @var{PIXELS} (greater than
+zero) to the edge of region.
+
+For example:
+@example
+ffmpeg -f x11grab -follow_mouse centered -r 25 -s cif -i :0.0 out.mpg
+
+# Follows only when the mouse pointer reaches within 100 pixels to edge
+ffmpeg -f x11grab -follow_mouse 100 -r 25 -s cif -i :0.0 out.mpg
 @end example
 
 @c man end INPUT DEVICES