Add Win32 GDI-based screen grabbing

Based on original code by Christophe Gisquet in 2010, updated to work
with current ffmpeg APIs.

Supports grabbing a single window or an area of the screen, including
support for multiple monitors (Windows does funky stuff with negative
coordinates here).

I've moved most of the configuration to AVOptions; the input file name
is now only the string "desktop", or "title=<windowname>" to select a
single window. The AVOptions are the same as x11grab where possible.

Code has been added to support a "show_region" mode, like x11grab, which
will draw a rectangle on the screen around the area being captured.

Instead of duplicating code for paletted image handling, I make use of
the GDI API's ability to output DIB (BMP) images, which can be run
through ffmpeg's existing BMP decoder.

Signed-off-by: Calvin Walton <calvin.walton@kepstin.ca>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

1 files changed, 630 insertions, 0 deletions

diff --git a/libavdevice/gdigrab.c b/libavdevice/gdigrab.c
new file mode 100644
index 0000000000..bccfef2c87
--- /dev/null
+++ b/libavdevice/gdigrab.c
@@ -0,0 +1,630 @@
+/*
+ * GDI video grab interface
+ *
+ * This file is part of FFmpeg.
+ *
+ * Copyright (C) 2013 Calvin Walton <calvin.walton@kepstin.ca>
+ * Copyright (C) 2007-2010 Christophe Gisquet <word1.word2@gmail.com>
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public License
+ * as published by the Free Software Foundation; either version 2.1
+ * of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+/**
+ * @file
+ * GDI frame device demuxer
+ * @author Calvin Walton <calvin.walton@kepstin.ca>
+ * @author Christophe Gisquet <word1.word2@gmail.com>
+ */
+
+#include "config.h"
+#include "libavformat/internal.h"
+#include "libavutil/opt.h"
+#include "libavutil/time.h"
+#include <windows.h>
+
+/**
+ * GDI Device Demuxer context
+ */
+struct gdigrab {
+    const AVClass *class;   /**< Class for private options */
+
+    int        frame_size;  /**< Size in bytes of the frame pixel data */
+    int        header_size; /**< Size in bytes of the DIB header */
+    AVRational time_base;   /**< Time base */
+    int64_t    time_frame;  /**< Current time */
+
+    int        draw_mouse;  /**< Draw mouse cursor (private option) */
+    int        show_region; /**< Draw border (private option) */
+    AVRational framerate;   /**< Capture framerate (private option) */
+    int        width;       /**< Width of the grab frame (private option) */
+    int        height;      /**< Height of the grab frame (private option) */
+    int        offset_x;    /**< Capture x offset (private option) */
+    int        offset_y;    /**< Capture y offset (private option) */
+
+    HWND       hwnd;        /**< Handle of the window for the grab */
+    HDC        source_hdc;  /**< Source device context */
+    HDC        dest_hdc;    /**< Destination, source-compatible DC */
+    BITMAPINFO bmi;         /**< Information describing DIB format */
+    HBITMAP    hbmp;        /**< Information on the bitmap captured */
+    void      *buffer;      /**< The buffer containing the bitmap image data */
+    RECT       clip_rect;   /**< The subarea of the screen or window to clip */
+
+    HWND       region_hwnd; /**< Handle of the region border window */
+
+    int cursor_error_printed;
+};
+
+#define WIN32_API_ERROR(str)                                            \
+    av_log(s1, AV_LOG_ERROR, str " (error %li)\n", GetLastError())
+
+#define REGION_WND_BORDER 3
+
+/**
+ * Callback to handle Windows messages for the region outline window.
+ *
+ * In particular, this handles painting the frame rectangle.
+ *
+ * @param hwnd The region outline window handle.
+ * @param msg The Windows message.
+ * @param wparam First Windows message parameter.
+ * @param lparam Second Windows message parameter.
+ * @return 0 success, !0 failure
+ */
+static LRESULT CALLBACK
+gdigrab_region_wnd_proc(HWND hwnd, UINT msg, WPARAM wparam, LPARAM lparam)
+{
+    PAINTSTRUCT ps;
+    HDC hdc;
+    RECT rect;
+
+    switch (msg) {
+    case WM_PAINT:
+        hdc = BeginPaint(hwnd, &ps);
+
+        GetClientRect(hwnd, &rect);
+        FrameRect(hdc, &rect, GetStockObject(BLACK_BRUSH));
+
+        rect.left++; rect.top++; rect.right--; rect.bottom--;
+        FrameRect(hdc, &rect, GetStockObject(WHITE_BRUSH));
+
+        rect.left++; rect.top++; rect.right--; rect.bottom--;
+        FrameRect(hdc, &rect, GetStockObject(BLACK_BRUSH));
+
+        EndPaint(hwnd, &ps);
+        break;
+    default:
+        return DefWindowProc(hwnd, msg, wparam, lparam);
+    }
+    return 0;
+}
+
+/**
+ * Initialize the region outline window.
+ *
+ * @param s1 The format context.
+ * @param gdigrab gdigrab context.
+ * @return 0 success, !0 failure
+ */
+static int
+gdigrab_region_wnd_init(AVFormatContext *s1, struct gdigrab *gdigrab)
+{
+    HWND hwnd;
+    RECT rect = gdigrab->clip_rect;
+    HRGN region = NULL;
+    HRGN region_interior = NULL;
+
+    DWORD style = WS_POPUP | WS_VISIBLE;
+    DWORD ex = WS_EX_TOOLWINDOW | WS_EX_TOPMOST | WS_EX_TRANSPARENT;
+
+    rect.left -= REGION_WND_BORDER; rect.top -= REGION_WND_BORDER;
+    rect.right += REGION_WND_BORDER; rect.bottom += REGION_WND_BORDER;
+
+    AdjustWindowRectEx(&rect, style, FALSE, ex);
+
+    // Create a window with no owner; use WC_DIALOG instead of writing a custom
+    // window class
+    hwnd = CreateWindowEx(ex, WC_DIALOG, NULL, style, rect.left, rect.top,
+            rect.right - rect.left, rect.bottom - rect.top,
+            NULL, NULL, NULL, NULL);
+    if (!hwnd) {
+        WIN32_API_ERROR("Could not create region display window");
+        goto error;
+    }
+
+    // Set the window shape to only include the border area
+    GetClientRect(hwnd, &rect);
+    region = CreateRectRgn(0, 0,
+            rect.right - rect.left, rect.bottom - rect.top);
+    region_interior = CreateRectRgn(REGION_WND_BORDER, REGION_WND_BORDER,
+            rect.right - rect.left - REGION_WND_BORDER,
+            rect.bottom - rect.top - REGION_WND_BORDER);
+    CombineRgn(region, region, region_interior, RGN_DIFF);
+    if (!SetWindowRgn(hwnd, region, FALSE)) {
+        WIN32_API_ERROR("Could not set window region");
+        goto error;
+    }
+    // The "region" memory is now owned by the window
+    region = NULL;
+    DeleteObject(region_interior);
+
+    SetWindowLongPtr(hwnd, GWLP_WNDPROC, (LONG_PTR) gdigrab_region_wnd_proc);
+
+    ShowWindow(hwnd, SW_SHOW);
+
+    gdigrab->region_hwnd = hwnd;
+
+    return 0;
+
+error:
+    if (region)
+        DeleteObject(region);
+    if (region_interior)
+        DeleteObject(region_interior);
+    if (hwnd)
+        DestroyWindow(hwnd);
+    return 1;
+}
+
+/**
+ * Cleanup/free the region outline window.
+ *
+ * @param s1 The format context.
+ * @param gdigrab gdigrab context.
+ */
+static void
+gdigrab_region_wnd_destroy(AVFormatContext *s1, struct gdigrab *gdigrab)
+{
+    if (gdigrab->region_hwnd)
+        DestroyWindow(gdigrab->region_hwnd);
+    gdigrab->region_hwnd = NULL;
+}
+
+/**
+ * Process the Windows message queue.
+ *
+ * This is important to prevent Windows from thinking the window has become
+ * unresponsive. As well, things like WM_PAINT (to actually draw the window
+ * contents) are handled from the message queue context.
+ *
+ * @param s1 The format context.
+ * @param gdigrab gdigrab context.
+ */
+static void
+gdigrab_region_wnd_update(AVFormatContext *s1, struct gdigrab *gdigrab)
+{
+    HWND hwnd = gdigrab->region_hwnd;
+    MSG msg;
+
+    while (PeekMessage(&msg, hwnd, 0, 0, PM_REMOVE)) {
+        DispatchMessage(&msg);
+    }
+}
+
+/**
+ * Initializes the gdi grab device demuxer (public device demuxer API).
+ *
+ * @param s1 Context from avformat core
+ * @return AVERROR_IO error, 0 success
+ */
+static int
+gdigrab_read_header(AVFormatContext *s1)
+{
+    struct gdigrab *gdigrab = s1->priv_data;
+
+    HWND hwnd;
+    HDC source_hdc = NULL;
+    HDC dest_hdc   = NULL;
+    BITMAPINFO bmi;
+    HBITMAP hbmp   = NULL;
+    void *buffer   = NULL;
+
+    const char *filename = s1->filename;
+    const char *name     = NULL;
+    AVStream   *st       = NULL;
+
+    int bpp;
+    RECT virtual_rect;
+    RECT clip_rect;
+    BITMAP bmp;
+    int ret;
+
+    if (!strncmp(filename, "title=", 6)) {
+        name = filename + 6;
+        hwnd = FindWindow(NULL, name);
+        if (!hwnd) {
+            av_log(s1, AV_LOG_ERROR,
+                   "Can't find window '%s', aborting.\n", name);
+            ret = AVERROR(EIO);
+            goto error;
+        }
+        if (gdigrab->show_region) {
+            av_log(s1, AV_LOG_WARNING,
+                    "Can't show region when grabbing a window.\n");
+            gdigrab->show_region = 0;
+        }
+    } else if (!strcmp(filename, "desktop")) {
+        hwnd = NULL;
+    } else {
+        av_log(s1, AV_LOG_ERROR,
+               "Please use \"desktop\" or \"title=<windowname>\" to specify your target.\n");
+        ret = AVERROR(EIO);
+        goto error;
+    }
+
+    if (hwnd) {
+        GetClientRect(hwnd, &virtual_rect);
+    } else {
+        virtual_rect.left = GetSystemMetrics(SM_XVIRTUALSCREEN);
+        virtual_rect.top = GetSystemMetrics(SM_YVIRTUALSCREEN);
+        virtual_rect.right = virtual_rect.left + GetSystemMetrics(SM_CXVIRTUALSCREEN);
+        virtual_rect.bottom = virtual_rect.top + GetSystemMetrics(SM_CYVIRTUALSCREEN);
+    }
+
+    /* If no width or height set, use full screen/window area */
+    if (!gdigrab->width || !gdigrab->height) {
+        clip_rect.left = virtual_rect.left;
+        clip_rect.top = virtual_rect.top;
+        clip_rect.right = virtual_rect.right;
+        clip_rect.bottom = virtual_rect.bottom;
+    } else {
+        clip_rect.left = gdigrab->offset_x;
+        clip_rect.top = gdigrab->offset_y;
+        clip_rect.right = gdigrab->width + gdigrab->offset_x;
+        clip_rect.bottom = gdigrab->height + gdigrab->offset_y;
+    }
+
+    if (clip_rect.left < virtual_rect.left ||
+            clip_rect.top < virtual_rect.top ||
+            clip_rect.right > virtual_rect.right ||
+            clip_rect.bottom > virtual_rect.bottom) {
+            av_log(s1, AV_LOG_ERROR,
+                    "Capture area (%li,%li),(%li,%li) extends outside window area (%li,%li),(%li,%li)",
+                    clip_rect.left, clip_rect.top,
+                    clip_rect.right, clip_rect.bottom,
+                    virtual_rect.left, virtual_rect.top,
+                    virtual_rect.right, virtual_rect.bottom);
+            ret = AVERROR(EIO);
+            goto error;
+    }
+
+    /* This will get the device context for the selected window, or if
+     * none, the primary screen */
+    source_hdc = GetDC(hwnd);
+    if (!source_hdc) {
+        WIN32_API_ERROR("Couldn't get window device context");
+        ret = AVERROR(EIO);
+        goto error;
+    }
+    bpp = GetDeviceCaps(source_hdc, BITSPIXEL);
+
+    if (name) {
+        av_log(s1, AV_LOG_INFO,
+               "Found window %s, capturing %lix%lix%i at (%li,%li)\n",
+               name,
+               clip_rect.right - clip_rect.left,
+               clip_rect.bottom - clip_rect.top,
+               bpp, clip_rect.left, clip_rect.top);
+    } else {
+        av_log(s1, AV_LOG_INFO,
+               "Capturing whole desktop as %lix%lix%i at (%li,%li)\n",
+               clip_rect.right - clip_rect.left,
+               clip_rect.bottom - clip_rect.top,
+               bpp, clip_rect.left, clip_rect.top);
+    }
+
+    if (clip_rect.right - clip_rect.left <= 0 ||
+            clip_rect.bottom - clip_rect.top <= 0 || bpp%8) {
+        av_log(s1, AV_LOG_ERROR, "Invalid properties, aborting\n");
+        ret = AVERROR(EIO);
+        goto error;
+    }
+
+    dest_hdc = CreateCompatibleDC(source_hdc);
+    if (!dest_hdc) {
+        WIN32_API_ERROR("Screen DC CreateCompatibleDC");
+        ret = AVERROR(EIO);
+        goto error;
+    }
+
+    /* Create a DIB and select it into the dest_hdc */
+    bmi.bmiHeader.biSize          = sizeof(BITMAPINFOHEADER);
+    bmi.bmiHeader.biWidth         = clip_rect.right - clip_rect.left;
+    bmi.bmiHeader.biHeight        = -(clip_rect.bottom - clip_rect.top);
+    bmi.bmiHeader.biPlanes        = 1;
+    bmi.bmiHeader.biBitCount      = bpp;
+    bmi.bmiHeader.biCompression   = BI_RGB;
+    bmi.bmiHeader.biSizeImage     = 0;
+    bmi.bmiHeader.biXPelsPerMeter = 0;
+    bmi.bmiHeader.biYPelsPerMeter = 0;
+    bmi.bmiHeader.biClrUsed       = 0;
+    bmi.bmiHeader.biClrImportant  = 0;
+    hbmp = CreateDIBSection(dest_hdc, &bmi, DIB_RGB_COLORS,
+            &buffer, NULL, 0);
+    if (!hbmp) {
+        WIN32_API_ERROR("Creating DIB Section");
+        ret = AVERROR(EIO);
+        goto error;
+    }
+
+    if (!SelectObject(dest_hdc, hbmp)) {
+        WIN32_API_ERROR("SelectObject");
+        ret = AVERROR(EIO);
+        goto error;
+    }
+
+    /* Get info from the bitmap */
+    GetObject(hbmp, sizeof(BITMAP), &bmp);
+
+    st = avformat_new_stream(s1, NULL);
+    if (!st) {
+        ret = AVERROR(ENOMEM);
+        goto error;
+    }
+    avpriv_set_pts_info(st, 64, 1, 1000000); /* 64 bits pts in us */
+
+    gdigrab->frame_size  = bmp.bmWidthBytes * bmp.bmHeight * bmp.bmPlanes;
+    gdigrab->header_size = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER) +
+                           (bpp <= 8 ? (1 << bpp) : 0) * sizeof(RGBQUAD) /* palette size */;
+    gdigrab->time_base   = av_inv_q(gdigrab->framerate);
+    gdigrab->time_frame  = av_gettime() / av_q2d(gdigrab->time_base);
+
+    gdigrab->hwnd       = hwnd;
+    gdigrab->source_hdc = source_hdc;
+    gdigrab->dest_hdc   = dest_hdc;
+    gdigrab->hbmp       = hbmp;
+    gdigrab->bmi        = bmi;
+    gdigrab->buffer     = buffer;
+    gdigrab->clip_rect  = clip_rect;
+
+    gdigrab->cursor_error_printed = 0;
+
+    if (gdigrab->show_region) {
+        if (gdigrab_region_wnd_init(s1, gdigrab)) {
+            ret = AVERROR(EIO);
+            goto error;
+        }
+    }
+
+    st->codec->codec_type = AVMEDIA_TYPE_VIDEO;
+    st->codec->codec_id   = AV_CODEC_ID_BMP;
+    st->codec->time_base  = gdigrab->time_base;
+    st->codec->bit_rate   = (gdigrab->header_size + gdigrab->frame_size) * 1/av_q2d(gdigrab->time_base) * 8;
+
+    return 0;
+
+error:
+    if (source_hdc)
+        ReleaseDC(hwnd, source_hdc);
+    if (dest_hdc)
+        DeleteDC(dest_hdc);
+    if (hbmp)
+        DeleteObject(hbmp);
+    if (source_hdc)
+        DeleteDC(source_hdc);
+    return ret;
+}
+
+/**
+ * Paints a mouse pointer in a Win32 image.
+ *
+ * @param s1 Context of the log information
+ * @param s  Current grad structure
+ */
+static void paint_mouse_pointer(AVFormatContext *s1, struct gdigrab *gdigrab)
+{
+    CURSORINFO ci = {0};
+
+#define CURSOR_ERROR(str)                 \
+    if (!gdigrab->cursor_error_printed) {       \
+        WIN32_API_ERROR(str);             \
+        gdigrab->cursor_error_printed = 1;      \
+    }
+
+    ci.cbSize = sizeof(ci);
+
+    if (GetCursorInfo(&ci)) {
+        HCURSOR icon = CopyCursor(ci.hCursor);
+        ICONINFO info;
+        POINT pos;
+        RECT clip_rect = gdigrab->clip_rect;
+        HWND hwnd = gdigrab->hwnd;
+
+        if (ci.flags != CURSOR_SHOWING)
+            return;
+
+        if (!icon) {
+            /* Use the standard arrow cursor as a fallback.
+             * You'll probably only hit this in Wine, which can't fetch
+             * the current system cursor. */
+            icon = CopyCursor(LoadCursor(NULL, IDC_ARROW));
+        }
+
+        if (!GetIconInfo(icon, &info)) {
+            CURSOR_ERROR("Could not get icon info");
+            goto icon_error;
+        }
+
+        pos.x = ci.ptScreenPos.x - clip_rect.left - info.xHotspot;
+        pos.y = ci.ptScreenPos.y - clip_rect.top - info.yHotspot;
+
+        if (hwnd) {
+            RECT rect;
+
+            if (GetWindowRect(hwnd, &rect)) {
+                pos.x -= rect.left;
+                pos.y -= rect.top;
+            } else {
+                CURSOR_ERROR("Couldn't get window rectangle");
+                goto icon_error;
+            }
+        }
+
+        av_log(s1, AV_LOG_DEBUG, "Cursor pos (%li,%li) -> (%li,%li)\n",
+                ci.ptScreenPos.x, ci.ptScreenPos.y, pos.x, pos.y);
+
+        if (pos.x >= 0 && pos.x <= clip_rect.right - clip_rect.left &&
+                pos.y >= 0 && pos.y <= clip_rect.bottom - clip_rect.top) {
+            if (!DrawIcon(gdigrab->dest_hdc, pos.x, pos.y, icon))
+                CURSOR_ERROR("Couldn't draw icon");
+        }
+
+icon_error:
+        if (icon)
+            DestroyCursor(icon);
+    } else {
+        CURSOR_ERROR("Couldn't get cursor info");
+    }
+}
+
+/**
+ * Grabs a frame from gdi (public device demuxer API).
+ *
+ * @param s1 Context from avformat core
+ * @param pkt Packet holding the grabbed frame
+ * @return frame size in bytes
+ */
+static int gdigrab_read_packet(AVFormatContext *s1, AVPacket *pkt)
+{
+    struct gdigrab *gdigrab = s1->priv_data;
+
+    HDC        dest_hdc   = gdigrab->dest_hdc;
+    HDC        source_hdc = gdigrab->source_hdc;
+    RECT       clip_rect  = gdigrab->clip_rect;
+    AVRational time_base  = gdigrab->time_base;
+    int64_t    time_frame = gdigrab->time_frame;
+
+    BITMAPFILEHEADER bfh;
+    int file_size = gdigrab->header_size + gdigrab->frame_size;
+
+    int64_t curtime, delay;
+
+    /* Calculate the time of the next frame */
+    time_frame += INT64_C(1000000);
+
+    /* Run Window message processing queue */
+    if (gdigrab->show_region)
+        gdigrab_region_wnd_update(s1, gdigrab);
+
+    /* wait based on the frame rate */
+    for (;;) {
+        curtime = av_gettime();
+        delay = time_frame * av_q2d(time_base) - curtime;
+        if (delay <= 0) {
+            if (delay < INT64_C(-1000000) * av_q2d(time_base)) {
+                time_frame += INT64_C(1000000);
+            }
+            break;
+        }
+        if (s1->flags & AVFMT_FLAG_NONBLOCK) {
+            return AVERROR(EAGAIN);
+        } else {
+            av_usleep(delay);
+        }
+    }
+
+    if (av_new_packet(pkt, file_size) < 0)
+        return AVERROR(ENOMEM);
+    pkt->pts = curtime;
+
+    /* Blit screen grab */
+    if (!BitBlt(dest_hdc, 0, 0,
+                clip_rect.right - clip_rect.left,
+                clip_rect.bottom - clip_rect.top,
+                source_hdc,
+                clip_rect.left, clip_rect.top, SRCCOPY | CAPTUREBLT)) {
+        WIN32_API_ERROR("Failed to capture image");
+        return AVERROR(EIO);
+    }
+    if (gdigrab->draw_mouse)
+        paint_mouse_pointer(s1, gdigrab);
+
+    /* Copy bits to packet data */
+
+    bfh.bfType = 0x4d42; /* "BM" in little-endian */
+    bfh.bfSize = file_size;
+    bfh.bfReserved1 = 0;
+    bfh.bfReserved2 = 0;
+    bfh.bfOffBits = gdigrab->header_size;
+
+    memcpy(pkt->data, &bfh, sizeof(bfh));
+
+    memcpy(pkt->data + sizeof(bfh), &gdigrab->bmi.bmiHeader, sizeof(gdigrab->bmi.bmiHeader));
+
+    if (gdigrab->bmi.bmiHeader.biBitCount <= 8)
+        GetDIBColorTable(dest_hdc, 0, 1 << gdigrab->bmi.bmiHeader.biBitCount,
+                (RGBQUAD *) (pkt->data + sizeof(bfh) + sizeof(gdigrab->bmi.bmiHeader)));
+
+    memcpy(pkt->data + gdigrab->header_size, gdigrab->buffer, gdigrab->frame_size);
+
+    gdigrab->time_frame = time_frame;
+
+    return gdigrab->header_size + gdigrab->frame_size;
+}
+
+/**
+ * Closes gdi frame grabber (public device demuxer API).
+ *
+ * @param s1 Context from avformat core
+ * @return 0 success, !0 failure
+ */
+static int gdigrab_read_close(AVFormatContext *s1)
+{
+    struct gdigrab *s = s1->priv_data;
+
+    if (s->show_region)
+        gdigrab_region_wnd_destroy(s1, s);
+
+    if (s->source_hdc)
+        ReleaseDC(s->hwnd, s->source_hdc);
+    if (s->dest_hdc)
+        DeleteDC(s->dest_hdc);
+    if (s->hbmp)
+        DeleteObject(s->hbmp);
+    if (s->source_hdc)
+        DeleteDC(s->source_hdc);
+
+    return 0;
+}
+
+#define OFFSET(x) offsetof(struct gdigrab, x)
+#define DEC AV_OPT_FLAG_DECODING_PARAM
+static const AVOption options[] = {
+    { "draw_mouse", "draw the mouse pointer", OFFSET(draw_mouse), AV_OPT_TYPE_INT, {.i64 = 1}, 0, 1, DEC },
+    { "show_region", "draw border around capture area", OFFSET(show_region), AV_OPT_TYPE_INT, {.i64 = 0}, 0, 1, DEC },
+    { "framerate", "set video frame rate", OFFSET(framerate), AV_OPT_TYPE_VIDEO_RATE, {.str = "ntsc"}, 0, 0, DEC },
+    { "video_size", "set video frame size", OFFSET(width), AV_OPT_TYPE_IMAGE_SIZE, {.str = NULL}, 0, 0, DEC },
+    { "offset_x", "capture area x offset", OFFSET(offset_x), AV_OPT_TYPE_INT, {.i64 = 0}, INT_MIN, INT_MAX, DEC },
+    { "offset_y", "capture area y offset", OFFSET(offset_y), AV_OPT_TYPE_INT, {.i64 = 0}, INT_MIN, INT_MAX, DEC },
+    { NULL },
+};
+
+static const AVClass gdigrab_class = {
+    .class_name = "GDIgrab indev",
+    .item_name  = av_default_item_name,
+    .option     = options,
+    .version    = LIBAVUTIL_VERSION_INT,
+};
+
+/** gdi grabber device demuxer declaration */
+AVInputFormat ff_gdigrab_demuxer = {
+    .name           = "gdigrab",
+    .long_name      = NULL_IF_CONFIG_SMALL("GDI API Windows frame grabber"),
+    .priv_data_size = sizeof(struct gdigrab),
+    .read_header    = gdigrab_read_header,
+    .read_packet    = gdigrab_read_packet,
+    .read_close     = gdigrab_read_close,
+    .flags          = AVFMT_NOFILE,
+    .priv_class     = &gdigrab_class,
+};