sACN / E1.31 module

This module is a simple sACN library that support the standard DMX message of the protocol. It is based on the 2016 version of the official ANSI E1.31 standard. It has support for sending out DMX data and receiving it. Multiple and multicast universes are supported. For full blown DMX support use OLA.

Currently missing features:

• discovery messages (receiving)
• E1.31 sync feature (on the receiver side)
• custom ports (because this is not recommended)

Features:

• out-of-order packet detection like the E1.31 6.7.2
• multicast
• auto flow control (see The Internals/Sending)
• E1.31 sync feature (see manual_flush)

Setup

This Package is in the pypi. To install the package use pip install sacn. Python 3.6 or newer required! To use the library import sacn. If you want to install directly from source, download or clone the repository and execute pip install . where the setup.py is located. For more information on pip installation see: https://packaging.python.org/tutorials/installing-packages/#installing-from-a-local-src-tree

The Internals

Sending

You can create a new sACNsender object and provide the necessary information. Then you have to use start(). This creates a new thread that is responsible for sending out the data. Do not forget to stop() the thread when finished! If the data is not changed, the same DMX data is sent out every second.

The thread sends out the data every 1/fps seconds. This reduces network traffic even if you give the sender new data more often than the fps. A simple description would be to say that the data that you give the sACNsender is subsampled by the fps. You can tweak this fps by simply change it when creating the sACNsender object.

This function works according to the E1.31. See 6.6.1 for more information.

Note: Since Version 1.4 there is a manual flush feature available. See Usage/Sending for more info. This feature also uses the sync feature of the sACN protocol (see page 36 on E1.31). Currently this is not implemented like the recommended way (this does not wait before sending out the sync packet), but it should work on a normal local network without too many latency differences. When the flush() function is called, all data is send out at the same time and immediately a sync packet is send out.

Receiving

A very simple solution, as you just create a sACNreceiver object and use start() a new thread that is running in the background and calls the callbacks when new sACN data arrives.

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Usage

Sending

To use the sending functionality you have to use the sACNsender.

import sacn
import time

sender = sacn.sACNsender()  # provide an IP-Address to bind to if you want to send multicast packets from a specific interface
sender.start()  # start the sending thread
sender.activate_output(1)  # start sending out data in the 1st universe
sender[1].multicast = True  # set multicast to True
# sender[1].destination = "192.168.1.20"  # or provide unicast information.
# Keep in mind that if multicast is on, unicast is not used
sender[1].dmx_data = (1, 2, 3, 4)  # some test DMX data

time.sleep(10)  # send the data for 10 seconds
sender.stop()  # do not forget to stop the sender

You can activate an output universe via activate_output(<universe>) and then change the attributes of this universe via sender[<universe>].<attribute>. To deactivate an output use deactivate_output(<universe>). The output is terminated like the E1.31 describes it on page 14.

If you want to flush manually and the sender thread should not send out automatic, use the sACNsender.manual_flush option. This is useful when you want to use a fixture that is using more than one universe and all the data on multiple universes should send out at the same time.

Tip: you can get the activated outputs with get_active_outputs() and you can move an output with all its settings from one universe to another with move_universe(<from>, <to>).

Available Attributes for sender[<universe>].<attribute> are:

• destination: str: the unicast destination as string. (eg "192.168.1.150") Default: "127.0.0.1"
• multicast: bool: set whether to send out via multicast or not. Default: False If True the data is send out via multicast and not unicast.
• ttl: int: the time-to-live for the packets that are send out via multicast on this universe. Default: 8
• priority: int: (must be between 0-200) the priority for this universe that is send out. If multiple sources in a network are sending to the same receiver the data with the highest priority wins. Default: 100
• preview_data: bool: Flag to mark the data as preview data for visualization purposes. Default: False
• dmx_data: tuple: the DMX data as a tuple. Max length is 512 and for legacy devices all data that is smaller than 512 is merged to a 512 length tuple with 0 as filler value. The values in the tuple have to be [0-255]!

sACNsender Creates a sender object. A sender is used to manage multiple sACN universes and handles their output. DMX data is send out every second, when no data changes. Some changes may be not send out, because the fps setting defines how often packets are send out to prevent network overuse. So if you change the DMX values too often in a second they may not all been send. Vary the fps parameter to your needs (Default=30).

• bind_address: str: the IP-Address to bind to. Provide an IP-Address to bind to if you want to send multicast packets from a specific interface.
• bind_port: int: optionally bind to a specific port. Default=5568. It is not recommended to change the port. Change the port number if you have trouble with another program or the sACNreceiver blocking the port
• source_name: str: the source name used in the sACN packets. See the standard for more information.
• cid: tuple: the cid. If not given, a random CID will be generated. See the standard for more information.
• fps: int the frames per second. See explanation above. Has to be >0. Default: 30
• universeDiscovery: bool if true, universe discovery messages are send out via broadcast every 10s. Default: True
• sync_universe: int set a specific universe used in the sync-packets. Default: 63999

When manually flushed, the E1.31 sync feature is used. So all universe data is send out, and after all data was send out a sync packet is send to all receivers and then they are allowed to display the received data. Note that not all receiver implemented this feature of the sACN protocol.

Example for the usage of the manual_flush:

import sacn
import time

sender = sacn.sACNsender()
sender.start()
sender.activate_output(1)
sender.activate_output(2)
sender[1].multicast = True
sender[2].multicast = True

sender.manual_flush = True # turning off the automatic sending of packets
sender[1].dmx_data = (1, 2, 3, 4)  # some test DMX data
sender[2].dmx_data = (5, 6, 7, 8)  # by the time we are here, the above data would be already send out,
# if manual_flush would be False. This could cause some jitter
# so instead we are flushing manual
time.sleep(1) # let the sender initialize itself
sender.flush()
sender.manual_flush = False # keep manual flush off as long as possible, because if it is on, the automatic
# sending of packets is turned off and that is not recommended
sender.stop() # stop sending out

Receiving

To use the receiving functionality you have to use the sACNreceiver.

import sacn
import time

# provide an IP-Address to bind to if you want to receive multicast packets from a specific interface
receiver = sacn.sACNreceiver()
receiver.start()  # start the receiving thread

# define a callback function
@receiver.listen_on('universe', universe=1)  # listens on universe 1
def callback(packet):  # packet type: sacn.DataPacket
    if packet.dmxStartCode == 0x00:  # ignore non-DMX-data packets
        print(packet.dmxData)  # print the received DMX data

# optional: if multicast is desired, join with the universe number as parameter
receiver.join_multicast(1)

time.sleep(10)  # receive for 10 seconds

# optional: if multicast was previously joined
receiver.leave_multicast(1)

receiver.stop()

The usage of the receiver is simpler than the sender. The sACNreceiver can be initialized with the following parameters:

• bind_address: str: Provide an IP-Address to bind to if you want to receive multicast packets from a specific interface. Note: This parameter is ignored on Linux when binding the socket to an address, but is used in subscribing the multicast group to a correct interface. If you have multiple interfaces within your system you will need to specify this parameter to ensure the multicast group join is completed on the correct interface and you receive sACN traffic.
• bind_port: int: Default: 5568. It is not recommended to change this value! Only use when you are know what you are doing!

Please keep in mind to not use the callbacks for time consuming tasks! If you do this, then the receiver can not react fast enough on incoming messages!

Functions:

• join_multicast(<universe>): joins the multicast group for the specific universe.
• leave_multicast(<universe>): leave the multicast group specified by the universe.
• get_possible_universes(): Returns a tuple with all universes that have sources that are sending out data and this data is received by this machine
• register_listener(<trigger>, <callback>, **kwargs): register a listener for the given trigger. You can also use the decorator listen_on(<trigger>, **kwargs). Possible trigger so far:
  • availability: gets called when there is no data for a universe anymore or there is now data available. This gets also fired if a source terminates a stream via the stream_termination bit. The callback should get two arguments: callback(universe, changed)
    • universe: int: is the universe where the action happened
    • changed: str: can be 'timeout' or 'available'
  • universe: registers a listener for the given universe. The callback gets only one parameter, the DataPacket. You can also use the decorator @listen_on('universe', universe=<universe>). The callback should have one argument: callback(packet)
    • packet: DataPacket: the received DataPacket with all information
• remove_listener(<callback>): removes a previously registered listener regardless of the trigger. This means a listener can only be removed completely, even if it was listening to multiple universes. If the function never was registered, nothing happens. Note: if a function was registered multiple times, this remove function needs to be called only once.
• remove_listener_from_universe(<universe>): removes all listeners from the given universe. This does only have effect on the 'universe' listening trigger. If no function was registered for this universe, nothing happens.

DataPacket

This is an abstract representation of an sACN Data packet that carries the DMX data. This class is used internally by the module and is used in the callbacks of the receiver.

The DataPacket provides following attributes:

• sourceName: str: a string that is used to identify the source. Only the first 64 bytes are used.
• priority: int: the priority used to manage multiple DMX data on one receiver. [1-200] Default: 100
• universe: int: the universe for the whole message and its DMX data. [1-63999]
• sequence: int: the sequence number. Should increment for every new message and can be used to check for wrong order of arriving packets.
• option_StreamTerminated: bool: True if this packet is the last one of the stream for the given universe.
• option_PreviewData: bool: True if this data is for visualization purposes.
• option_ForceSync: bool: True if this should only function in a synchronized state.
• dmxStartCode: int: the start code for the data tuple. [1-255] Default: 0x00 for streaming level data. See Alternate START Codes for more information.
• dmxData: tuple: the DMX data as tuple. Max length is 512 and shorter tuples getting normalized to a length of 512. Filled with 0 for empty spaces.

Development

Some tools are used to help with development of this library. These are flake8, pytest and coverage.py.

Install those tools with pip:

pip install flake8 pytest pytest-timeout coverage

flake8 checks for formatting issues and can be run with flake8 or python -m flake8 in the root directory of this repository.

pytest is used for unit testing and can be executed with pytest or python -m pytest in the root directory of this repository. By default, this skips the integration test, which uses real hardware I/O and might not run in every configuration. Use the flag --run-integration-tests to run the additional tests (e.g. python -m pytest --run-integration-tests)

It is useful to check if the test coverage changed with coverage run -m pytest and then coverage html, which generates a htmlcov/index.html file with all the information.

Changelog

• 1.9.1: When a sACN packet could not be send out, the exception is raised instead of silently dropped. (Thanks to andrewyager! See #48 for more information)
• 1.9.0: The behavior of multicast sending and receiving is now unified across most operating systems. This means Windows no longer requires to set a bind_address to be able to use multicast or universe discovery. (Thanks to mthespian! See #42 for more information)
• 1.8.1: Calling stop on a sender or receiver now closes the underlying socket too. Note: after stopping a sender or receiver, it can not be started again with start. (See #39 for more information)
• 1.8.0: Added function for removing a listener on a receiver by universe. See sACNreceiver.remove_listener_from_universe(<universe>) for more information.
• 1.7.1: Small changes that might improve timing on the sender. (Thanks to mthespian! See #36 for more information)
• 1.7.0: Added function for removing a listener on a receiver. See sACNreceiver.remove_listener(<callback>) for more information.
• 1.6.4: Functionality related to sending of sACN data is now mostly covered by tests. Removed undocumented parameters for sACNsender.start().
• 1.6.3: Functionality related to receiving sACN data is now mostly covered by tests. Fixed a bug, where an exception was thrown on the first DataPacket when the stream-termination option was set. (Additional thanks to mthespian! See #31 for more information)
• 1.6.2: Test coverage of sub-module messages is now 100%. Fixed a bug where a too long source name did not throw an exception. Fixed a bug where invalid DMX data could be set on the DataPacket. (Thanks to mthespian! See #30 for more information)
• 1.6.1: Fixed a bug, where the DMX start code was not set on received packets (Thanks to mthespian! See #29 for more information)
• 1.6: Added dmxStartCode property to DataPacket (Thanks to mthespian! see #27 for more information)
• 1.5: Performance improvement: Deleted debugging statements in hot path of packet sending and receiving (Thanks to shauneccles! See #25 for more information)
• 1.4.6: Fix: When creating a DataPacket with invalid DMX start codes (i.e. not 0x00) an exception is thrown (Thanks to niggiover9000! See #11 for more information)
• 1.4.5: When using a manual flush, only a specified list of universes can be flushed (Thanks to CrazyIvan359! See #22 for more information)
• 1.4.4: The universe used for the sACN-sync messages can now be set when creating a sACNsender (Thanks to CrazyIvan359! See #21 for more information)
• 1.4.3: The sequence number of the sync-packet when using manual flush was not increased (Thanks to @BlakeGarner ! See #19 for more information)
• 1.4.2: The internal logging of the receiver_thread and output_thread was using the root logger instead of its module-logger. (Thanks to @mje-nz ! See #18 for more information)
• 1.4: Added a manual flush feature for sending out all universes at the same time. Thanks to ahodges9 for the idea.