Zextras Video Server

The Zextras Video Server is a WebRTC stream aggregator that improves Team’s performance by merging and decoding/re-encoding all streams in a Meeting.

While the default WebRTC creates one incoming and one outgoing stream per meeting participant, with the Zextras Video Server, each client will only have one aggregated inbound stream and one aggregated outbound stream. This applies for both video and audio.


In our simple scenario, 5 people are participating in a meeting.

  • Without Video Server: each client generates 4x outgoing video/audio streams and receives 4 incoming video/audio streams

  • With Video Server: each client generates 1 outgoing video/audio stream and receives 1 incoming video/audio stream

In summary:

Video Server

Incoming Connections

Outgoing Connections


4 (1 from each other client)

4 (1 to each other client)




By default, the Video Server uses conservative Codecs (VP8 and Opus) to ensure the broadest compatibility, but more codecs can be enabled. It also splits the Webcam and Screen Sharing streams and reserves the same bandwidth for both.

A properly set up Video Server will supersede the need of a TURN server, provided that all clients can reach the Video Server’s public IP and that UDP traffic is not filtered.


The Zextras Video Server must be installed on a dedicated server and has the following requirements:

  • Minimum 4 CPU cores, suggested at least 8 to handle more than 100 users at the same time

  • 1024mb of ram + 1mb of ram for each connected user


The Zextras Video Server mainly scales on the CPU, so more CPU cores and power means more connected users.

  • A public IP

  • A publicly resolvable FQDN

  • With the default settings, 200kb/s (0.2 mb/s) bandwidth for each connected user

  • WebSockets

  • The mailbox server will establish a WebSocket on port 8188 (TCP) to communicate with the Video Server

  • Connecting browsers will use a random UDP port between 20000 and 40000 on the public IP of the Zextras Video Server


The Video Server installer requires the fully qualified hostname to be correctly configured in /etc/hosts and /etc/hostname. Failing to comply will likely cause the sample commands provided at the end of the installation to be incorrect.

Client Configuration

No client configuration is needed, as the Team Zimlet will autonomously detect whether a video server is set up an use it if available.


  • Download the installer package for the Linux distribution on which Zextras Suite is installed (RHEL 7 and CentOS 7 RHEL 8 and CentOS 8 Ubuntu 18.04)

  • Copy the installer package to the server

  • Unpack the installer package, adapting the name in the example below by repacing [OS] with the proper string: r7, r8, or u18 :

    # tar zxvf videoserver-[OS].tgz
  • Enter the unpacked directory: cd videoserver-installer

  • Run the installation script: ./install.sh

    ~/videoserver-installer# ./install.sh

    This script will install Zextras Video Server, and all its runtime dependencies onto the running system.

    System will be modified, would you like to proceed? [Y]

  • The installer will first checks for the needed dependencies and installs any missing one, if found. A message like:

    software-properties-common not found. Would you like to install it? [Y]

    Press Y to install them

  • You will be then prompted to install the actual Video Server packages:

    Would you like to install Zextras VideoServer? [Y]

    Again, press Y to install them

  • Once all packages are installed, you will be asked the Public IP Address of the video server.


    The Public IP Address is either the IP address of the video server, if it is directly accessible from remote clients on the Internet, or—​if there is a NAT-ting device in front of it (e.g., a firewall or router)–the IP address with which the video server is reachable.

    This is the only bit of configuration required. The installer will set up the Video Server and then return two commands that must be executed on any Mailbox Server of the infrastructure to set up the connection with the Video Server and enable it for all servers:

    Please execute these commands in a mailbox node as zimbra user
    to complete the setup of the video server:

    Copy and execute them, and refer to ZxTeam CLI Commands for details about the syntax and additional options in case you want to customise it.

Architecture and Service Control

A Team meeting is hosted on one mailbox, which also keeps the state of the meeting. It is a responsibility of that mailbox to communicate with a videoserver instance to start a meeting and controlling it.

Therefore, each mailbox has its own connection pool, which can be controlled via the ZxTeam CLI Commands. The commands to control the service are straightforward:

  • Start the connection pool:

    zxsuite team doStartService team-videoserver-pool
  • Shutdown the connection pool:

    zxsuite team doStopService team-videoserver-pool
  • Check a connection pool status. This command reports information about the node on which it is executed.

    $ zxsuite team clusterstatus
         isFullySynced                                       true
                 id                                           123
                 hostname                                     <ip_videoserver>:8188
                 status                                       online
                 local_meetings_hosted                        2

    The output of this command contains this information:

    • Should the remote Video Server be offline or unreachable, the status will be offline instead of online.

    • last failure shows an error message (e.g., Unauthorized request (wrong or missing secret/token) or a generic Runtime Exception) if the last connection attempt to the videoserver was unsuccessful. The message is cleared when the connection is successful.

    • local_meetings_hosted reports the number of meetings hosted on the current mailbox.

Video Server Scaling

Starting with Zextras Suite 3.1.8 (Video Server package version 0.10.5) it is possible to run multiple videoservers on the same infrastructure.

To add a new Video Server to the configuration, run the Video Server installer on a new server and follow the instructions - the installer will provide the required commands (zxsuite team video-server add with the appropriate parameters) needed to add the server to the infrastructure once packages are installed.

To remove a Video Server from the configuration, use the zxsuite team video-server remove command from any mailbox server - this will remove the appropriate entries from the Zextras Config (manual package removal on the video server is required).


When using multiple video servers, meetings are instanced on any of the available instances.

CLI Commands

The CLI command to manage Video Server installations is zxsuite team with the parameter video-server and the parameters video-server add and video-server remove respectively.

Quick reference:

# zxsuite team video-server add *videoserver.example.com* [param VALUE[,VALUE]]

# zxsuite team video-server remove *videoserver.example.com* [param VALUE[,VALUE]]

Bandwidth and Codecs

Video Bandwidth

The administrator can set the webcam stream quality and the screenshare stream quality specifing the relative bitrate in Kbps. The values must be at least 100 Kbps and can be increased as desired.

Higher values mean more quality but more used bandwidth.

  • zxsuite config global set attribute teamChatWebcamBitrateCap value 200: is the command for the webcam stream quality/bandwidth

  • zxsuite config global set attribute teamChatScreenBitrateCap value 200: is the command for the screenshare stream qualitybandwidth


By default both the webcam bandwidth and the screen sharing bandwidth are set to 200 Kbps.

Video Codecs

By default, the VP8 video codec is used. This is to ensure the best compatibility, as this codec is available in all supported browsers, but other codecs can be enabled:

  • AV1: zxsuite config global set attribute teamChatVideoCodecAV1 value true

  • H264: zxsuite config global set attribute teamChatVideoCodecH264 value true

  • H265: zxsuite config global set attribute teamChatVideoCodecH265 value true

  • VP8: zxsuite config global set attribute teamChatVideoCodecVP8 value true

  • VP9: zxsuite config global set attribute teamChatVideoCodecVP9 value true

Only one codec can be enabled at the time, so before enabling a new codec remember to disable the previous one using the same command as the one in the list above but substituting value true with value false.

E.g. to enable the H264 codec run:

zxsuite config global set attribute teamChatVideoCodecVP8 value false

zxsuite config global set attribute teamChatVideoCodecH264 value true

Audio Codec

The audio codec used by the Zextras Video Server is Opus. No other codecs are supported, as Opus is currently the only reliable one available across all supported browsers.

Advanced settings

The following settings influence the audio experience.

Audio Quality

The administrator can set the Opus audio quality by setting the sampling rate (in Hz) in the teamChatAudioSamplingRate global attribute.

The available values are:

  • 8000 → represents the narrowband bandwidth

  • 12000 → represents the mediumband bandwidth

  • 16000 → represents the wideband bandwidth (default)

  • 24000 → represents the superwideband bandwidth

  • 48000 → represents the fullband bandwidth

Audio Sensitivity

The administrator can optimize the audio sensitivity with these two commands:

zxsuite config global set attribute teamChatAudioLevelSensitivity value 55

zxsuite config global set attribute teamChatAudioSamplingSensitivityInterval value 10

The audio level sensitivity defines how much the audio should be normalized between all the audio sources. The value has a range between 0 and 100 where 0 represents the audio muted and 100 the maximum audio level (too loud).

By default the value is set to 55, which is also the value suggested for optimal performances

The audio sampling sensitivity interval defines the interval in seconds used to compute the audio sensitivity level. By default the value is set to 2 seconds, this means that the video server normalizes the audio level considering the audio sources of the last 2 seconds.

The value should be at least 0, but it should be set to 10 seconds to provide the best performances.