![]() ![]() For various reasons, no single renderer is preferable in all scenarios. Choosing the Right Renderer With DirectX 9.0, DirectShow provides four separate video renderers: the old Video Renderer, the Overlay Mixer, the VMR-7 and the VMR-9. Also, some video cards cannot perform Direct3D operations when the display is set to 24 bits per pixel. ![]() The VMR cannot be put into a run state if the monitor is set for 256 colors. * Note The VMR requires that the system monitor be set for a color depth of at least 16 bits. Hardware-accelerated video (support for DirectX Video Acceleration) decoding. Support for an RGB overlay or the ability to blend to a YUV overlay surface. The actual amount of memory required is dependent on the image size of the video streams and resolution of the display mode being used. At least 16MB of video memory if multiple video streams are to be blended together. The ability to StretchBlt from YUV to RGB DirectDraw surfaces. Graphics cards that perform well with the VMR have the following hardware support built into them: - Support for YUV and "non-power of 2" Direct3D texture surfaces. When taking advantage of the new features offered by the VMR, particularly blending of multiple video streams and/or application images, the overall performance obtained is highly dependent on the capabilities of the graphics card being used on the computer. VMR System Requirements The VMR uses the graphics-processing capabilities of the computer's display card exclusively the VMR does not perform any blending or rendering of video using the host processor, because to do so would greatly impact the frame rate and quality of the video being displayed. The VMR also employs a new image presentation mechanism which is designed for current and future generations of adapters, which have support for Direct3D, increased VRAM and video memory bandwidth, and hardware acceleration features. The VMR is more robust than the earlier renderers, in part because it only uses DirectDraw 7 (or Direct3D 9 if you are using the VMR-9) interfaces, as opposed to the old renderers which used a mixture of interfaces from older and newer versions of DirectDraw. The VMR is capable of true alpha blending, and can create multiple overlays in software in addition to the hardware overlays. ![]() Because it does not have a window manager, it must use a second filter, the Video Renderer, for window management. The Overlay Mixer performs destination color keying, but it is not capable of alpha blending. This filter only uses the hardware overlay on the graphics card, and so is generally limited to the one overlay surface provided by most cards. In scenarios involving either a video port or multiple video input streams, prior to the VMR the Overlay Mixer filter was used for rendering. Neither the VMR-7 nor the VMR-9 ever uses GDI for rendering the VMR-7 is based completely on DirectDraw 7 and the VMR-9 is based on Direct3D 9. This is done either to conserve video resources, which were much more limited five years ago, or else to overcome limitations in DirectDraw that were related to multi-monitor support. In certain scenarios, it uses GDI for rendering. It was based on graphics hardware technology which is now over five years old, and on an older version of DirectDraw. The Video Renderer filter was used to render a single video stream in non-video port scenarios. Previous DirectShow Renderers With the old filters, different renderers would be required in the graph depending on the hardware configuration. The primary difference is that the original VMR (now called the VMR-7) uses DirectDraw 7 internally to control the video hardware, while the new version of VMR (called the VMR-9) uses Direct3D 9. The two VMR filters are very similar in their implementation and the interfaces that they expose. Beginning with DirectX 9.0, a separate version of the VMR, called the VMR-9, is available for redistribution on all platforms supported by DirectX. The VMR was first made available for the Windows XP platforms only. The VMR replaces the Overlay Mixer and Video Renderer, and adds many new mixing features. VMR (Video Mixing Renderer) In terms of both performance and breadth of features, the Video Mixing Renderer (VMR) filter represents the next generation in video rendering on the Windows platform. ![]()
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