[FFmpeg-devel] [PATCH] x11grab: capture a window instead of the whole screen

[Paul B Mahol]

Looks fine.


On Tue, Jan 26, 2021 at 11:24 AM <sgerwk-at-aol.com at ffmpeg.org> wrote:

> In my previous email the patch got mangled by the web mail interface, so I
> am
> sending it again. Sorry for the duplicate.
>
> This patch allows ffmpeg to capture a specific window instead of the whole
> screen. An example:
>
> ffmpeg -f x11grab -window_id 0xa00000a -i :0 output.mp4
>
> ---
>   doc/indevs.texi       |  3 +++
>   libavdevice/xcbgrab.c | 19 ++++++++++++-------
>   2 files changed, 15 insertions(+), 7 deletions(-)
>
> diff --git a/doc/indevs.texi b/doc/indevs.texi
> index 3924d03..0738919 100644
> --- a/doc/indevs.texi
> +++ b/doc/indevs.texi
> @@ -1564,6 +1564,9 @@ With @var{follow_mouse}:
>   ffmpeg -f x11grab -follow_mouse centered -show_region 1 -framerate 25
> -video_size cif -i :0.0 out.mpg
>   @end example
>
> + at item window_id
> +Grab this window, instead of the whole screen.
> +
>   @item video_size
>   Set the video frame size. Default is the full desktop.
>
> diff --git a/libavdevice/xcbgrab.c b/libavdevice/xcbgrab.c
> index 95bdc8a..6e4ef5d 100644
> --- a/libavdevice/xcbgrab.c
> +++ b/libavdevice/xcbgrab.c
> @@ -60,6 +60,7 @@ typedef struct XCBGrabContext {
>       AVRational time_base;
>       int64_t frame_duration;
>
> +    xcb_window_t window_id;
>       int x, y;
>       int width, height;
>       int frame_size;
> @@ -82,6 +83,7 @@ typedef struct XCBGrabContext {
>   #define OFFSET(x) offsetof(XCBGrabContext, x)
>   #define D AV_OPT_FLAG_DECODING_PARAM
>   static const AVOption options[] = {
> +    { "window_id", "Window to capture", OFFSET(window_id),
> AV_OPT_TYPE_INT, { .i64 = 0 }, 0, INT_MAX, D },

      { "x", "Initial x coordinate.", OFFSET(x), AV_OPT_TYPE_INT, { .i64 =
> 0 }, 0, INT_MAX, D },
>       { "y", "Initial y coordinate.", OFFSET(y), AV_OPT_TYPE_INT, { .i64 =
> 0 }, 0, INT_MAX, D },
>       { "grab_x", "Initial x coordinate.", OFFSET(x), AV_OPT_TYPE_INT, {
> .i64 = 0 }, 0, INT_MAX, D },
> @@ -157,7 +159,7 @@ static int xcbgrab_frame(AVFormatContext *s, AVPacket
> *pkt)
>       XCBGrabContext *c = s->priv_data;
>       xcb_get_image_cookie_t iq;
>       xcb_get_image_reply_t *img;
> -    xcb_drawable_t drawable = c->screen->root;
> +    xcb_drawable_t drawable = c->window_id;
>       xcb_generic_error_t *e = NULL;
>       uint8_t *data;
>       int length;
> @@ -267,7 +269,7 @@ static int xcbgrab_frame_shm(AVFormatContext *s,
> AVPacket *pkt)
>       XCBGrabContext *c = s->priv_data;
>       xcb_shm_get_image_cookie_t iq;
>       xcb_shm_get_image_reply_t *img;
> -    xcb_drawable_t drawable = c->screen->root;
> +    xcb_drawable_t drawable = c->window_id;
>       xcb_generic_error_t *e = NULL;
>       AVBufferRef *buf;
>       xcb_shm_seg_t segment;
> @@ -566,7 +568,7 @@ static int create_stream(AVFormatContext *s)
>
>       avpriv_set_pts_info(st, 64, 1, 1000000);
>
> -    gc  = xcb_get_geometry(c->conn, c->screen->root);
> +    gc  = xcb_get_geometry(c->conn, c->window_id);
>       geo = xcb_get_geometry_reply(c->conn, gc, NULL);
>       if (!geo)
>           return AVERROR_EXTERNAL;
> @@ -745,7 +747,7 @@ static int select_region(AVFormatContext *s)
>               press_position = (xcb_point_t){ press->event_x,
> press->event_y };
>               rectangle.x = press_position.x;
>               rectangle.y = press_position.y;
> -            xcb_poly_rectangle(conn, root_window, gc, 1, &rectangle);
> +            xcb_poly_rectangle(conn, c->window_id, gc, 1, &rectangle);
>               was_pressed = 1;
>               break;
>           }
> @@ -754,14 +756,14 @@ static int select_region(AVFormatContext *s)
>                   xcb_motion_notify_event_t *motion =
>                       (xcb_motion_notify_event_t *)event;
>                   xcb_point_t cursor_position = { motion->event_x,
> motion->event_y };
> -                xcb_poly_rectangle(conn, root_window, gc, 1, &rectangle);
> +                xcb_poly_rectangle(conn, c->window_id, gc, 1, &rectangle);
>                   rectangle = rectangle_from_corners(&press_position,
> &cursor_position);
> -                xcb_poly_rectangle(conn, root_window, gc, 1, &rectangle);
> +                xcb_poly_rectangle(conn, c->window_id, gc, 1, &rectangle);
>               }
>               break;
>           }
>           case XCB_BUTTON_RELEASE: {
> -            xcb_poly_rectangle(conn, root_window, gc, 1, &rectangle);
> +            xcb_poly_rectangle(conn, c->window_id, gc, 1, &rectangle);
>               done = 1;
>               break;
>           }
> @@ -825,6 +827,9 @@ static av_cold int xcbgrab_read_header(AVFormatContext
> *s)
>           return AVERROR(EIO);
>       }
>
> +    if (c->window_id == 0)
> +        c->window_id = c->screen->root;
> +
>       if (c->select_region) {
>           ret = select_region(s);
>           if (ret < 0) {
> --
> 2.29.2
>
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