[FFmpeg-devel] [PATCH v2] gdigrab: Allow capturing a window by its handle

[Lena]

Added the change to the documentation and added error checking on `strtol`, according to the stdlib documentation.

The documentation for `strtol` says that on error, 0 is returned. This makes it impossible to specify a window handle of 0 (the whole desktop), but that case is already covered by the "desktop" input filename, so it should be fine.


x11grab can capture windows by their ID, but gdigrab can only capture windows by their names, internally calling FindWindowW to lookup its handle.

This patch simply allows the user to specify a window handle directly.
Signed-off-by: Lena <lena at nihil.gay>
---
 doc/indevs.texi       |  8 ++++++--
 libavdevice/gdigrab.c | 13 ++++++++++++-
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/doc/indevs.texi b/doc/indevs.texi
index 863536a34d..6da0ccac62 100644
--- a/doc/indevs.texi
+++ b/doc/indevs.texi
@@ -722,7 +722,7 @@ Win32 GDI-based screen capture device.
 
 This device allows you to capture a region of the display on Windows.
 
-There are two options for the input filename:
+There are three options for the input filename:
 @example
 desktop
 @end example
@@ -730,9 +730,13 @@ or
 @example
 title=@var{window_title}
 @end example
+or
+ at example
+hwnd=@var{window_hwnd}
+ at end example
 
 The first option will capture the entire desktop, or a fixed region of the
-desktop. The second option will instead capture the contents of a single
+desktop. The second and third options will instead capture the contents of a single
 window, regardless of its position on the screen.
 
 For example, to grab the entire desktop using @command{ffmpeg}:
diff --git a/libavdevice/gdigrab.c b/libavdevice/gdigrab.c
index c069232472..f310d8f3d7 100644
--- a/libavdevice/gdigrab.c
+++ b/libavdevice/gdigrab.c
@@ -273,9 +273,20 @@ gdigrab_read_header(AVFormatContext *s1)
         }
     } else if (!strcmp(filename, "desktop")) {
         hwnd = NULL;
+    } else if (!strncmp(filename, "hwnd=", 5)) {
+        name = filename + 5;
+        
+        hwnd = strtol(name, NULL, 0);
+
+        if (hwnd == NULL) {
+            av_log(s1, AV_LOG_ERROR,
+               "Invalid window handle.\n");
+            ret = AVERROR(EINVAL);
+            goto error;
+        }
     } else {
         av_log(s1, AV_LOG_ERROR,
-               "Please use \"desktop\" or \"title=<windowname>\" to specify your target.\n");
+               "Please use \"desktop\", \"title=<windowname>\" or \"hwnd=<hwnd>\" to specify your target.\n");
         ret = AVERROR(EIO);
         goto error;
     }
-- 
2.43.0