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Kramer VP-551x HDMI switcher

CCRMA’s Classroom and Seminar Room handle video source selection with a Kramer VP-551x HDMI switcher (manufacturer’s product page) that lives inside a rolling rack with several connectors on the front and back to let you plug in a wide variety of sources such as phones and laptops. (For the [Stage][Stage]’s two projectors there’s instead a Kramer VS62HA (manufacturer’s VS62HA product page).)

A document camera, Blu-Ray/DVD player, and CCRMA Linux Machine are permanently connected and always available as audio and/or video sources.

Commonly needed additional cables hang coiled from hooks on the side and commonly needed adapters live in the glass cookie jar on the desk.

Basic AV usage

  1. Plug in video source (e.g., laptop HDMI), if any, to a numbered video input. (Your laptop will immediately “see” the Kramer as an external display (and possible HDMI audio destination) even if it is not selected, possibly rearranging windows, etc.)
  2. Select the desired input on the Kramer (possibly Linux, DVD, Document Camera…)
  3. Now the corresponding audio-over-HDMI is coming through the mixer (if your laptop is using HDMI for audio output, e.g., VP-551x or DisplayPort)
  4. (Otherwise you can use your device’s probably-not-great headphone jack through the provided 1/8” (3.5mm) stereo unbalanced analog (wired into its own pair of mixer inputs); this route does not involve the Kramer.)

Video Source Selection

The Seminar Room’s Kramer VP-551x HDMI switcher and some of its input sockets.

A Kramer VP-551x HDMI switcher allows you to select any one video source, by pressing the square button above the corresponding label:

Corresponds to the HDMI socket labeled HDMI 1, just below the Kramer
Corresponds to the HDMI socket labeled HDMI 2, just below the Kramer
Corresponds to the HDMI socket labeled HDMI 3, on the back of the rack holding the Kramer. In the Classroom this is the “Zoom” Mac mini.
The video from the CCRMA Linux Machine (mirroring what’s on the video monitor, thanks to a hardware splitter)
Document Camera
The Elmo Visual Presenter P30S document camera (manual)
The Oppo BDP103 Blu-Ray / DVD / CD player
Corresponds to the VGA socket labeled VGA, just below the Kramer

Whichever one source is selected will appear on the video projector. XXX some day it will also be mirrored on the HDMI socket labeled OUTPUT on the back of the rack.

The one selected video source might include audio-over-HDMI. (Linux, Document Camera, and VGA do not use this.) The stereo audio from this one HDMI source (if any) comes into the audio system as HDMI.

Audio System

The Kramer itself just has an analog stereo audio output (from the selected HDMI source, possibly just silence) that we connect to the mixer in the Classroom or Seminar Room.


The Kramer went into the Seminar Room November 22, 2021 and into the Classroom January 21, 2022. Prior to this an Extron-based system provided similar functionality (but with independent selection of one stereo audio source instead of now having a separate mixer adding HDMI, analog, and other audio sources).

This page of CCRMA documentation last committed on Mon Jan 9 12:34:56 2023 -0800 by Matthew James Wright. Stanford has a page for Digital Accessibility.