ioctl VIDIOC_G_FBUF, VIDIOC_S_FBUF &manvol; VIDIOC_G_FBUF VIDIOC_S_FBUF Get or set frame buffer overlay parameters int ioctl int fd int request struct v4l2_framebuffer *argp int ioctl int fd int request const struct v4l2_framebuffer *argp fd &fd; request VIDIOC_G_FBUF, VIDIOC_S_FBUF argp Applications can use the VIDIOC_G_FBUF and VIDIOC_S_FBUF ioctl to get and set the framebuffer parameters for a Video Overlay or Video Output Overlay (OSD). The type of overlay is implied by the device type (capture or output device) and can be determined with the &VIDIOC-QUERYCAP; ioctl. One /dev/videoN device must not support both kinds of overlay. The V4L2 API distinguishes destructive and non-destructive overlays. A destructive overlay copies captured video images into the video memory of a graphics card. A non-destructive overlay blends video images into a VGA signal or graphics into a video signal. Video Output Overlays are always non-destructive. To get the current parameters applications call the VIDIOC_G_FBUF ioctl with a pointer to a v4l2_framebuffer structure. The driver fills all fields of the structure or returns an &EINVAL; when overlays are not supported. To set the parameters for a Video Output Overlay, applications must initialize the flags field of a struct v4l2_framebuffer. Since the framebuffer is implemented on the TV card all other parameters are determined by the driver. When an application calls VIDIOC_S_FBUF with a pointer to this structure, the driver prepares for the overlay and returns the framebuffer parameters as VIDIOC_G_FBUF does, or it returns an error code. To set the parameters for a non-destructive Video Overlay, applications must initialize the flags field, the fmt substructure, and call VIDIOC_S_FBUF. Again the driver prepares for the overlay and returns the framebuffer parameters as VIDIOC_G_FBUF does, or it returns an error code. For a destructive Video Overlay applications must additionally provide a base address. Setting up a DMA to a random memory location can jeopardize the system security, its stability or even damage the hardware, therefore only the superuser can set the parameters for a destructive video overlay. &cs-ustr; __u32 capability Overlay capability flags set by the driver, see . __u32 flags Overlay control flags set by application and driver, see void * base Physical base address of the framebuffer, that is the address of the pixel in the top left corner of the framebuffer.A physical base address may not suit all platforms. GK notes in theory we should pass something like PCI device + memory region + offset instead. If you encounter problems please discuss on the linux-media mailing list: &v4l-ml;. This field is irrelevant to non-destructive Video Overlays. For destructive Video Overlays applications must provide a base address. The driver may accept only base addresses which are a multiple of two, four or eight bytes. For Video Output Overlays the driver must return a valid base address, so applications can find the corresponding Linux framebuffer device (see ). &v4l2-pix-format; fmt Layout of the frame buffer. The v4l2_pix_format structure is defined in , for clarification the fields and acceptable values are listed below: __u32 width Width of the frame buffer in pixels. __u32 height Height of the frame buffer in pixels. __u32 pixelformat The pixel format of the framebuffer. For non-destructive Video Overlays this field only defines a format for the &v4l2-window; chromakey field. For destructive Video Overlays applications must initialize this field. For Video Output Overlays the driver must return a valid format. Usually this is an RGB format (for example V4L2_PIX_FMT_RGB565) but YUV formats (only packed YUV formats when chroma keying is used, not including V4L2_PIX_FMT_YUYV and V4L2_PIX_FMT_UYVY) and the V4L2_PIX_FMT_PAL8 format are also permitted. The behavior of the driver when an application requests a compressed format is undefined. See for information on pixel formats. &v4l2-field; field Drivers and applications shall ignore this field. If applicable, the field order is selected with the &VIDIOC-S-FMT; ioctl, using the field field of &v4l2-window;. __u32 bytesperline Distance in bytes between the leftmost pixels in two adjacent lines. This field is irrelevant to non-destructive Video Overlays.For destructive Video Overlays both applications and drivers can set this field to request padding bytes at the end of each line. Drivers however may ignore the requested value, returning width times bytes-per-pixel or a larger value required by the hardware. That implies applications can just set this field to zero to get a reasonable default.For Video Output Overlays the driver must return a valid value.Video hardware may access padding bytes, therefore they must reside in accessible memory. Consider for example the case where padding bytes after the last line of an image cross a system page boundary. Capture devices may write padding bytes, the value is undefined. Output devices ignore the contents of padding bytes.When the image format is planar the bytesperline value applies to the largest plane and is divided by the same factor as the width field for any smaller planes. For example the Cb and Cr planes of a YUV 4:2:0 image have half as many padding bytes following each line as the Y plane. To avoid ambiguities drivers must return a bytesperline value rounded up to a multiple of the scale factor. __u32 sizeimage This field is irrelevant to non-destructive Video Overlays. For destructive Video Overlays applications must initialize this field. For Video Output Overlays the driver must return a valid format.Together with base it defines the framebuffer memory accessible by the driver. &v4l2-colorspace; colorspace This information supplements the pixelformat and must be set by the driver, see . __u32 priv Reserved for additional information about custom (driver defined) formats. When not used drivers and applications must set this field to zero. &cs-def; V4L2_FBUF_CAP_EXTERNOVERLAY 0x0001 The device is capable of non-destructive overlays. When the driver clears this flag, only destructive overlays are supported. There are no drivers yet which support both destructive and non-destructive overlays. V4L2_FBUF_CAP_CHROMAKEY 0x0002 The device supports clipping by chroma-keying the images. That is, image pixels replace pixels in the VGA or video signal only where the latter assume a certain color. Chroma-keying makes no sense for destructive overlays. V4L2_FBUF_CAP_LIST_CLIPPING 0x0004 The device supports clipping using a list of clip rectangles. V4L2_FBUF_CAP_BITMAP_CLIPPING 0x0008 The device supports clipping using a bit mask. V4L2_FBUF_CAP_LOCAL_ALPHA 0x0010 The device supports clipping/blending using the alpha channel of the framebuffer or VGA signal. Alpha blending makes no sense for destructive overlays. V4L2_FBUF_CAP_GLOBAL_ALPHA 0x0020 The device supports alpha blending using a global alpha value. Alpha blending makes no sense for destructive overlays. V4L2_FBUF_CAP_LOCAL_INV_ALPHA 0x0040 The device supports clipping/blending using the inverted alpha channel of the framebuffer or VGA signal. Alpha blending makes no sense for destructive overlays. V4L2_FBUF_CAP_SRC_CHROMAKEY 0x0080 The device supports Source Chroma-keying. Framebuffer pixels with the chroma-key colors are replaced by video pixels, which is exactly opposite of V4L2_FBUF_CAP_CHROMAKEY &cs-def; V4L2_FBUF_FLAG_PRIMARY 0x0001 The framebuffer is the primary graphics surface. In other words, the overlay is destructive. [?] V4L2_FBUF_FLAG_OVERLAY 0x0002 The frame buffer is an overlay surface the same size as the capture. [?] The purpose of V4L2_FBUF_FLAG_PRIMARY and V4L2_FBUF_FLAG_OVERLAY was never quite clear. Most drivers seem to ignore these flags. For compatibility with the bttv driver applications should set the V4L2_FBUF_FLAG_OVERLAY flag. V4L2_FBUF_FLAG_CHROMAKEY 0x0004 Use chroma-keying. The chroma-key color is determined by the chromakey field of &v4l2-window; and negotiated with the &VIDIOC-S-FMT; ioctl, see and . There are no flags to enable clipping using a list of clip rectangles or a bitmap. These methods are negotiated with the &VIDIOC-S-FMT; ioctl, see and . V4L2_FBUF_FLAG_LOCAL_ALPHA 0x0008 Use the alpha channel of the framebuffer to clip or blend framebuffer pixels with video images. The blend function is: output = framebuffer pixel * alpha + video pixel * (1 - alpha). The actual alpha depth depends on the framebuffer pixel format. V4L2_FBUF_FLAG_GLOBAL_ALPHA 0x0010 Use a global alpha value to blend the framebuffer with video images. The blend function is: output = (framebuffer pixel * alpha + video pixel * (255 - alpha)) / 255. The alpha value is determined by the global_alpha field of &v4l2-window; and negotiated with the &VIDIOC-S-FMT; ioctl, see and . V4L2_FBUF_FLAG_LOCAL_INV_ALPHA 0x0020 Like V4L2_FBUF_FLAG_LOCAL_ALPHA, use the alpha channel of the framebuffer to clip or blend framebuffer pixels with video images, but with an inverted alpha value. The blend function is: output = framebuffer pixel * (1 - alpha) + video pixel * alpha. The actual alpha depth depends on the framebuffer pixel format. V4L2_FBUF_FLAG_SRC_CHROMAKEY 0x0040 Use source chroma-keying. The source chroma-key color is determined by the chromakey field of &v4l2-window; and negotiated with the &VIDIOC-S-FMT; ioctl, see and . Both chroma-keying are mutual exclusive to each other, so same chromakey field of &v4l2-window; is being used. &return-value; EPERM VIDIOC_S_FBUF can only be called by a privileged user to negotiate the parameters for a destructive overlay. EBUSY The framebuffer parameters cannot be changed at this time because overlay is already enabled, or capturing is enabled and the hardware cannot capture and overlay simultaneously. EINVAL The ioctl is not supported or the VIDIOC_S_FBUF parameters are unsuitable.