Video Renderers and their Meaning in Zoom Player


Introduction:
Zoom Player supports quite a few Video Rendering technologies (technologies which draw video on your screen). This article gives detailed information with regards to each technology, its benefits and its shortcomings. But before we delve into the actual renderers, here's a brief preface detailing some of the technologies behind the video renderers.


The Video Overlay:
At around 1995, when MPEG1 (VCD) playback started to become popular on the PC, the actual processing power of the PC was not quite strong enough to play such content. The display card manufacturers at the time came up with a solution called "The Video Overlay". The Video Overlay is a special hardware on the display card which is used to perform several video-display features in hardware (Stretching, Color-Space Conversion, etc...), thus allowing smooth playback of video at no cost to the CPU.

The Image quality of the Video Overlay really depends on the hardware of the display card. I've found Video Overlay quality to be sub-par in pretty much all display cards on the market today.

One of the biggest downsides to using a video rendering technology based on The Video Overlay is that there is only one Video Overlay unit on the display card. This makes the technology very inappropriate for Multi-Monitor systems.


Direct3D:
Direct3D is part of the Microsoft DirectX libraries which give programmers access to an ever evolving feature-set. With the release of DirectX version 9, Microsoft created a new set of features that provide the hardware capabilities similar to overlay surfaces but without many of the limitations.

Video Rendering technologies based on Direct3D provide better image quality than Video Overlay implementations and don't suffer from the single-monitor issues of the Video Overlay. However, support for Direct3D video-display technologies is rather recent. Not all cards support this technology and even cards that do, don't always support the entire feature-set.

As a general point of reference, I would recommend at least an NVIDIA GF4 ti4200 or an ATI Radeon 9xxx card (Cards that support the Pixel Shader technology).


The System Default Renderer:
When playing media files in Zoom Player Standard playback mode, using the System Default renderer means "Standard Overlay" under any version of windows older than Windows XP and "VMR7" when using Windows XP.


The Standard Overlay Renderer:
This is the oldest Video Rendering technology. It uses The Video Overlay when it is available and can fall back to Pure-CPU handling of the video when The Video Overlay is unavailable. Pure-CPU handling of video means that the CPU will be used instead of the Video Overlay hardware with a massive hit on playback (CPU works much harder).

The downside to this renderer is that it doesn't support proper Aspect Ratio controls, Hardware Color Controls (Hue/Saturation/Brightness/Contrast/Gamma) are inaccessible and screen captures are flaky.


The Overlay Mixer Renderer:
Still using the Video Overlay technology, this renderer allows access to Hardware Color Controls (Hue/Saturation/Brightness/Contrast/Gamma) to cards that support color controls in hardware. Some cards may support only a subset of the color control features (only Brightness for example). This renderer also support proper Aspect Ratio controls for formats that require it (VCD/SVCD/DVD/Etc...).

The downside to this renderer is that it can't fall back to Pure-CPU. If the Video Overlay is inaccessible, it just won't work. In Media Mode Zoom Player will fall back to the Standard Overlay Renderer if this is the case. In DVD Mode, you'll get an error saying that the Video Decoder is unable to connect to the Overlay Mixer.

Lastly, this rendering technology is not very good at screen captures.


The Video Mixing Renderer 7 (VMR7)
This renderer is a hybrid of the Video Overlay technology and the Direct3D technology. It is only available on Windows XP and has been superseded by the VMR9. This is the rendering technology used by the Microsoft Media Player versions 7-10.

By default this rendering technology uses the Video Overlay. However, if it is inaccessible, it can use Direct3D to some degree.

The downside to this renderer is that it doesn't give access to Color Controls and it's not very good at screen captures.


The Video Mixing Renderer 9 (VMR9)
This is the latest technology in Video Rendering. It's completely based on Direct3D, requires DirectX-9 and recent hardware to operate. It can potentially give the best image quality (depends on the rendering mode and the display card hardware). VMR9 gives access to hardware color controls (if the card supports it) but not to Gamma controls as Microsoft didn't include support for it. VMR9 also has the best Aspect Ratio controls.

VMR9 supports three distinct rendering modes:


VMR9: Windowed
This is the most basic mode. It is available for backward compatibility. It does not give you access to Frame Capturing. One thing about this mode is that there was a bug in Windows XP-SP1 and DirectX-9b which made this mode the only mode in which DVD Menu navigation works. With Windows XP-SP2 and DirectX-9c the DVD Menu navigation bug was fixed.


VMR9: Windowless
This mode is slightly more advanced than the Windowed mode and is the best mode in which to conduct screen captures.


VMR9: Renderless
This is the most complex VMR9 rendering mode. It can work in Direct3D exclusive mode which means the entire machine is set to fullscreen and no background application are allowed access to the video hardware. Under Direct3D Exclusive Mode, less CPU is required to play videos and depending on the resolution of the video, playback may be smoother. The downside is that in Direct3D Exclusive mode, your computer is wholly dedicated to video playback and you won't be able to perform any other tasks.

Current versions of Zoom Player may not support the VMR9 Renderless mode, but should in the near future.