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

[sgerwk at aol.com]

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