The Video Renderer is the component used to display video on your Monitor/TV. Each Video Renderer component has its benefits and its limitations (which you can read about here). In general, the "Overlay Mixer" is the most compatible but can have inferior image quality and is limited to one video playing at a time and only on the primary monitor (it will display a black screen when playing on a secondary monitor or when another video is already playing). VMR9 has better image quality but it requires DirectX-9 installed (a microsoft component) and display hardware (Graphic Card) capable of supporting certain DirectX-9 specific capabilities.
If you're having video issues, try switching the video renderer to "VMR9 Windowless". Under certain conditions, VMR9 may make some video content appear "washed out" (black will look gray, image may look as if the contrast isn't set properly). This is caused by Display Driver issues. Updating the drivers may help, and if not, there are work-around detailed in the Inmatrix Forum.
Audio Renderer (audio device)
The Audio Renderer is the component used to output audio to your Speakers or Sound System. Each Audio Device (Sound Card) in your system may have two or more Audio Renderer components listed. Under most situations, the Audio Renderer should be set to "Default DirectSound Device" (the audio device set as primary by windows), but if you have multiple audio devices on your system, you can select a specific device from the list.
Under rare conditions (usually with older, less compatible audio devices) you may want to select the "Default WaveOut Device". Only do this if you're experiencing audio glitches. Changing the volume with a WaveOut device selected will change the system volume level (DirectSound devices have no impact on the system volume level).
Use the Internal Audio Processing DSP Filter (required for using the equalizer)
When enabled, Zoom Player will make use of its internal Audio DSP component in order to support such functions as Audio Equalizer, PreAmp (digital audio amplification) and Audio stream switching in media files. On very rare conditions the DSP component may cause audio problems and can be disabled here.