[FFmpeg-devel] [PATCH v3] gdigrab: Allow capturing a window by its handle

[Stefano Sabatini]

On date Thursday 2023-12-14 11:32:44 +0100, Lena wrote:
> Updated the wording of the documentation, and added error checking for strtol.
> 
> I looked at how other parts of the codebase check for errors on strtol and implemented it that way (iec61883, filter_units_bsf, etc).
> 
> As for checking if the string value is larger/smaller than a long, i don't think there's a need, as the documentation says it'd just get set to LONG_MIN/LONG_MAX and fail anyway.
> 
> 
> 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 | 15 ++++++++++++++-
>  2 files changed, 20 insertions(+), 3 deletions(-)
> 
> diff --git a/doc/indevs.texi b/doc/indevs.texi
> index 863536a34d..a0c684f545 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:
> +Amongst options for the imput filenames are such elements as:
>  @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..3153b6f711 100644
> --- a/libavdevice/gdigrab.c
> +++ b/libavdevice/gdigrab.c
> @@ -273,9 +273,22 @@ gdigrab_read_header(AVFormatContext *s1)
>          }
>      } else if (!strcmp(filename, "desktop")) {
>          hwnd = NULL;
> +    } else if (!strncmp(filename, "hwnd=", 5)) {
> +        name = filename + 5;
> +        char *p;
> +
> +        hwnd = strtol(name, &p, 0);
> +
> +        if (p == NULL || p == name || p[0] == '\0')
> +        {
> +            av_log(s1, AV_LOG_ERROR,

> +                   "Invalid window handle.\n");

Here you can provide some context:
"Invalid window handle '%s', must be an valid integer.", name

Looks good otherwise, thanks.