sendscreen 1.7

Display local desktop on remove host over LAN without VGA/HDMI cable

NAME

sendscreen - Display local desktop on remove host over LAN without VGA/HDMI cable

SYNOPSIS

sendscreen [-vrf] [-s host] [-p port] [-W width] [-H height] [-F #]
  -v       verbose mode
  -r       receiver mode
  -f       full speed mode (no frame rate limit)
  -s host  specify receiver hostname/address
  -p port  port number
  -W #     screen width (default: 800 [pixel])
  -H #     screen height (default: 600 [pixel])
  -F #     maximum frame rate (default: 10 [frame/second])

DESCRIPTION

This manual page documents sendscreen, a Python program to continuously capture and transmit the desktop to remote host over LAN (Local Area Networking) using UDP (User Datagram Protocol).

sendscreen was developed to eliminate hassles at research meetings in our laboratory. At a meeting, participants bring their own laptops, and during a meeting, they repeatedly (1) take the VGA/HDMI video cable connected to the LCD projector, (2) plug the VGA/HDMI video connector to his/her laptop, (3) enable the external video output (e.g., by pressing Fn + F7), (4) unplug the VGA/HDMI video connector, and (5) pass it to another participant. Such awkward procedure had been endlessly performed during the meeting. With sendscreen, you no longer need to worry about the video cable and enabling the external video output on your laptop.

sendscreen works either as a sender or a receiver.
sendscreen works as a sender by default, and it repeatedly capture the desktop and send the zlib-compressed image (frame) to the receiver. When invoked with -r option, sendscreen works as a receiver. It waits for incoming frame data over LAN. When it receives the frame data from a sender, the frame is uncompressed and displayed on the screen of the receiver.

USAGE

On a computer connected with the LCD projector:

sendscreen -r

On a client computer:

sendscreen -s server_name

where server_name is the hostname or the IP address of the receiver.

sendscreen uses the UDP protocol with port 5000 by default. Please make sure that the sender reaches the port 5000 of the receiver using the UDP protocol; i.e., disalbe the network firewall and packet filtering (e.g., iptagles -F; iptables -X).

OPTIONS

• -v

  Verbose mode. sendscreen will display additional information during execution.

• -r

  Receiver mode. sendscreen receives frames from a sender in your LAN.

• -f

  Full throttle mode. sendscreen tries to send frames as fast as possible.

• -s host

  Specify receiver's hostname or IP address.

• -p port

  Port number at which the receiver receives frame data.

• -w width

  Specify the screen width (default: 800 [pixel]).

• -h height

  Specify the screen height (default: 600 [pixel]).

• -F rate

  Maximum frate rate is limited by rate (default: 5 [frame/s])

REQUIREMENTS

sendscreen runs on X Window System. It uses Xlib, pygame, and rgbconv modules as well as several Python standard modules. sendsceeen assumes a TrueType font is available at `/usr/share/fonts/truetype/freefont/FreeSans.ttf', which is included in fonts-freefont-ttf package in Debian GNU/Linux although sendscreen works with any TrueType font.

INTERNALS

sendscreen uses its original message format for transferring a frame image from a sender to the receiver. A message is composed of a 48-byte header and a compressed frame image. A raw frame image is WIDTH x HEIGHT pixels in RGBX format, which means that the size of every pixel is 32-bit.

A sender of sendscreen repeatedly captures its root window using Xlib's XGetImage in ZPixmap format. A captured image is converted from the BGRX format to the RGBX format using rgbconv Python module. A raw frame image is compressed using zlib. A message composed of the message header and the compressed frame image is sent to the receiver as a series of UDP datagrams, whose maximum size is specified by MAX_SEGMENT_SIZE variable.

sendscreen implements two transmission modes: full-image and delta-image modes. In full-image mode, a raw frame image captured by the sender is fully sent to the receiver. On the contrary, in delta-image mode, only the difference between the current image frame and the previous image frame is sent to the receiver. In most cases, the screen of the sender is not much dynamic, so using the delta-image mode significantly reduces the amount of data transferred from the sender to the receiver. The current implementation of sendscreen sends in the full-image mode once every five seconds.

The receiver of sendscreen continuously waits for incoming UDP datagrams. If it successfully receives a message from a sender, the message is decoded and the compressed frame image is decompressed. The raw frame image is then displayed in the window of the receiver. When the receiver receives no message for one second, the window of the receiver is turned blue to indicate NO SIGNAL reception from any sender. Note that sendscreen does not require any authentication or handshaking, so multiple sendscreen senders can simultaneously connect to the receiver, which is very handy since the receiver requires no intervention from a user to switch among different sendscreen senders.

INSTALLATION

$ pip3 install sendscreen

AVAILABILITY

The latest version of sendscreen is available at PyPI (https://pypi.org/project/sendscreen/) .

SEE ALSO

xset(1)

AUTHOR

Hiroyuki Ohsaki <ohsaki[atmark]lsnl.jp>