Using liveCaster to multicast textual attributes

(For instructions on how to multicast MPEG audio data, see here) When running in 'attribute' mode, liveCaster uses a multicast channel to 'announce' the contents of a file system directory (i.e., folder). This directory should contain one or more text files (with suffix ".txt"), each describing a data record to be announced over the multicast channel. These data records each consist of a set of textual attributes: (name,value) pairs.

Example 1: Announcing stock prices

In this example, a directory - named "stocks" - contains two files "ACME.txt" and "RNDM.txt", each describing the stock price of a (hypothetical) company.

Contents of the file "ACME.txt":

info    ACME Enterprises, Inc.
high	13.25
low     12.875
last	13.125
time	1/30/1998 3:59pm

Contents of the file "RNDM.txt":

info    Random Software Corporation
high	37.5
low     11.25
last	ll.25
time	1/30/1998 3:55pm

Example 2: Announcing weather data

In this example, a directory - named "weather" - contains a file "SFO.txt" describing the current weather conditions in San Francisco.

Contents of the file "SFO.txt":

nickname San Francisco
{current conditions} partly cloudy
tempF 58

Notes

In each (non-blank) line of the file, the first word (up to white-space) is the name of an attribute; the remaining words, if any, form its value. (However, an attribute name containing white-space can be described by enclosing it in braces, as in example 2 above.) Each attribute name must be followed only by white-space, not a colon or comma.
The order of attribute lines within a file is unimportant.
One special attribute - called "nickname" - is defined for every file. By default, its value is the name of the file, without the ".txt" suffix. However, the "nickname" attribute can also be redefined explicitly, as in example 2 above.
Attributes of the directory itself are described in a special file called "SELF.txt". This file is created automatically by liveCaster, but you may also add more attributes to this file.

You may create and modify these ".txt" files using any method of your choosing. You could, for example, simply use a text editor. Alternatively, you could use a separate program - perhaps connected to a sensor or other data feed - to update these files. liveCaster will automatically notice when a file has been modified; it will then start announcing the new attribute value(s). liveCaster will also notice when new ".txt" files are added, and/or previously existing ".txt" files are deleted.

At present, liveCaster is intended for multicasting small pieces of textual information - not large files. liveCaster will exit with an error message if it sees a ".txt" file that's larger than a predetermined limit (currently, 2000 bytes).

Specifying a directory to announce

Upon starting liveCaster, you will see a dialog that you can use to navigate to the directory that you wish to announce. Once you're inside this directory, click the "Choose the current directory" button. (If the directory that you wish to announce does not yet exist, you can create it - as a subdirectory of the current directory - by clicking the "Create New" button.)

Alternatively, you can specify the directory to announce by starting liveCaster with the -d <directory path> command line option. (<directory path> must be a directory that already exists.) This option is useful if you wish to launch liveCaster automatically from a script.

Specifying the directory parameters

If the directory is being announced for the first time, you will then be presented with a second dialog ("Enter directory parameters"), which will give you the opportunity to set (or change) the network parameters for the announcement. This dialog is preset with default values. If you're happy with these values, click "OK" (or type the <Enter> or <Return> key). The parameters are described below:

directory id: A character-string network identifier for this directory. If yours is the only (or first) machine to be announcing this directory, then this field should be left at its preset value. If, however, more than one machine is announcing into the same directory, then each machine's liveCaster must use the same "directory id".
multicast address, port: The IP multicast address and UDP port number to be used for this directory. These are preset with arbitrarily chosen values; you may change these if you wish.
(At present, the preset multicast address is chosen randomly from an infrequently used range, so it is possible (although unlikely) that this address is already being used. LIVE555.COM is working within the IETF to define standard protocols and APIs for allocating multicast addresses. Future versions of liveCaster will use these as they're defined.)
It is also possible to specify a unicast address. In this case liveCaster will send its data (unicast) to the specified address and port.
scope (TTL): This menu can be used to change the scope of your intended audience
average bandwidth: The average rate (in bits per second) at which this directory's data will be multicast. This value is computed as a function of the TTL, and (currently) cannot be changed, except by varying the TTL. This bandwidth is defined as 40,000/(TTL+1) bits per second. This is conservatively low, to ensure that even computers with low-bandwidth Internet connections can make wide-ranging announcements, without significantly degrading their connections.
network data format: How the attributes are stored in multicast packets. At present, one such format is supported: MAFP.
announcement protocol: At present, one protocol is supported: "mk_default_dir_sharer" - the default directory sharing protocol used by the (now obsolete) multikit directory browser. (This is a simple multicast announcement protocol, similar to SAP. Announcements are repeated indefinitely, with no feedback from recipients.)
description (optional): A (human-readable) description of the directory. (If present, this will become the "info" attribute.)
intended view type: This indicates how the recipients should display the data. The default setting - "itemized" - has no effect; the other settings - "positional" and "customized" - will set the directory's "viewType" attribute accordingly.

liveCaster stores these parameters in the directory's "SELF.txt" file.

When liveCaster is running

In normal operation (after a directory has been selected and its parameters set up) liveCaster will display a small window, indicating the directory that is currently being announced.

This window may be minimized (and liveCaster will continue running in the background). To exit liveCaster, delete this window, or type <Control>-q.

Running liveCaster without a GUI

Receiving and viewing liveCaster's attribute announcements

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