Audio Back Channel (ABC) Plugin documentation

1. Destination

The ABC plugin may be used to create a uni/bidirectional (full duplex) audio communication between different components of the GeViScope/re_porter environment. Application scenarios are for example:

the uni/bidirectional audio communication of a GSCView station with GeViScope devices. This may be used for example for announcements from CCTV workstations to railway stations where GeViScopes are installed (announcement function).
the uni/bidirectional audio communication between two GSCView workstations (audio chat function)
(not) CCTV related audio broadcast function (for example shopping mall announcements or even entertainment with recorded audio multimedia material) (thin audio client function)

The ABC function is not thought to replace professional Intercom technology. Its principal transmission latency of about 500ms makes real intercom applications inconvenient. It just represents a simple means to transmit audio from a GSCView workstation to other devices which have the necessary ABC plugin software installed. Nevertheless the architectural approach of the feature allows quite flexible communication scenarios.

2. Communication architecture

The ABC function is implemented as a GeViScope media plugin device. It requires the availability of the ABC plugin on the system which is to output the audio backchannel on its loudspeakers (ABC output). To access the audio source a GSCServer must be installed on the system which represents the input of the audio backchannel (ABC source). The audio device may be a microphone or any other audio component which may be connected to the PC audio input. This architectural approach allows different application scenarios which are to be explained in the following paragraphs together with the necessary setup parameters in both the ABC source and the ABC output.

The ABC function is working completely independent of the DSP audio inputs of GeViScope. It may be used even if GeViscope/re_porter is not using its audio inputs (unidirectional audio for example for the announcement function). In the following just the ABC function is explained. The common audio functions of the GSC/re_porter system are not influenced and may be used as accustomed.

2.1. GSCView → GSC

2.1.1 General architecture

The image shows the basic communication architecture of ABC. In that installation the function may be used to send audio from a microphone on the GSCView workstationto either:

1. a fixed (but connected) GeViScope independently from the video presentation

2. the GeViScope which has the video channel which is presented in the active viewer of GSCView

3. all GeViScopes which are currently connected to GSCView (audio broadcast)

The ABC behaviour 1,2 or 3 may be parametrized in GSCView and is dependent on the setup for the ABC control buttons. ABC works in the following way:

The audio source for ABC is realized by a (virtual) GSCServer which must be installed on the ABC source system.
This virtual server offers an audio media channel which may be accessed remotely. The input microphone is connected to that media channel.
GSCView (or any other GSC action source - for example Multimap, GeViSoft or GSCSDK based applications) transmits ABC Control Actions to the ABC output system. These actions contain the IP address (or network name) of the ABC source system.
The ABC actions are forwarded to the ABC plugin which must be installed on the ABC output system.
The ABC plugin gets the IP address of the ABC source and connects to it via the GSCDBI interface. Then it searches the ABC source for a audio channel which it is to output. If an audio source channel was found the ABC plugin starts the audio transmission and feeds the audio to the local loudspeaker output.
If the ABC plugin gets an ABC_disconnect action or if it gets a new ABC_connect action the old audio stream is closed and if necessary the new one is opened.

To get that function running there is some setup work (GSCSetup ABC source, GSCSsetup ABC output, Setup GSCView) necessary which is described in the following instructions.

2.1.2 Installation step by step

The following describes a step by step setup for the application scenario of this paragraph. Based on that example the realization of other types of applications (like an GSCView ↔ GSCView intercommunication) should be simple.

ABC source

Before starting you should make sure that the system audio channel is working at all and the microphone input is processed by Windows. A test with the Windows audio recorder function shows that.

a) (virtual) GSCServer setup

Install GSCServer on the ABC source system
Start GSCSetup and connect to the GSCServer on the ABC source system.
Move to the “Hardware” dialog.
Add a virtual channel. For example you can use any IP camera type for that. It just provides a placeholder for the ABC function.
Check the “Use system audio” box in the belonging “Hardware settings” dialog. This assigns the system audio input to that media channel.
Save the setup
Move to the “Media Channels” dialog.
Add the virtual media channel to the list.
Change the name of that channel to the default name for the ABC function (AUDIOBACKCHANNEL)
Move to the live streaming function dialog of that channel
Select “High” for the “Audio profile” of the live stream.

After that the source system offers a network audio channel.

b) GSCView setup

Open the GSCView profile manager
Select the menu “Custom buttons”
Create a custom button

Caption Speak
Action on mouse down ABC_Connect(”ABC source address”)
Action on mouse up ABC_Disconnect()
Send to Server of selected viewer

ABC source address in the ABC_Connect actions represents the IP address or network name of the ABC source system. If the button is pressed the “Action on mouse down” is sent to the remote GSC. Its ABC plugin receives it and connects to the IP address parameter of the ABC_Connect Attention: Do not mix up the IP addresses of the ABC source and ABC output system. If the button is released that action is as well transmitted to the remote GSC.It tells the ABC plugin to close the IP connection and henceforth to mute the audio transmission.

If you would like to connect the ABC just to a fixed server you can select it in the “Send to” option of the “Speak” button. This could perhaps be necessary in an installation where multiple GSCs are remotely installed at the same site but just one has a loudspeaker connected.

ABC output

On the GSC which is to output an ABC channel do the following:

Before starting you should make sure that the system audio output is working at all. Connect a loudspeaker and try to play an audio sample with the media player.

Copy the ABC plugin (AudioBackChannel.dll) to the directory mediaplugins (in the GEVISCOPE system folder).
Start GSCSetup and connect to the GSCServer on the ABC output system
Move to the “Hardware” dialog.
Open the menu item “Add” in the context menu. Select “Add”. This shows a list of available media plugins. Select the ABC plugin.
Save that setup to the GeViScope. It is NOT necessary to setup a “Media channel” for that plugin as it is accustomed for normal devices.

That procedure must be done on each GSC which is to output audio from the ABC source system.

2.1.3 Parameters of the ABC plugin

In the hardware dialog of the ABC output system you may adjust some parameters which control the behaviour of the audio backchannel:

Default volume	Defines the default loudness of the audio output
GSCChannel	That is the name of the audio channel on the ABC source system. The default is AUDIOBACKCHANNEL
GSC user name GSC password	The connection between the ABC plugin and the ABC source server needs a normal GSC account. The default is “sysadmin” “masterkey”. If you want to use another account you can change it here. That account must be available in the setup of the ABC source system
Prebuffer latency Runtime latency	These parameters influence the audio transmission latency. To have an audio transmission without stream interruption a certain buffering is necessary. If there are audio interruptions you may reduce them by increasing the latencies

2.1.4 ABC Actions

ABC is controled by special ABC-actions. These actions may be created by any software which interfaces either GeViScope or GeViSoft. This needs not to be just GSCView but may be used in Multimap or SDK clients as well to control the establishment of ABC audio connections. If for example Multimap is used to control GSCView remotely you may add ABC control buttons to Multimap maps instead of controling ABC from GSCView. You may even use MBEG or any other hardware / software interface of GeViSoft to control the ABC function.

ABC connections are controled by the following GSC actions:

ABC_Connect(“ABC source address”)
Instructs the remote ABC plugin to connect to the audio channel auf the ABC source. A new ABC_Connect action overwrites the old connection.
ABC_Disconnect()
Disconnects the ABC connection on that GSC where it is sent to.

3. ABC Extensions (07/2008)

3.1 Action controled playing of pre-recorded audio files

May be used to play audio files (WAV) controled by any action and action mapping in GSC
Alternative to the direct speech between GSCView and GSC. May be used in GSCView as well alternatively to the direct microphone connection. Has advantages in the following situations:

- Low bandwidth connections between GSCView and GSC. The ABC live channel needs a minimum of 128 kbit / second. Playing of predefined audio files does not consume bandwidth

- the surveillance staff has no possibility to misuse the live function or to make stupid audio comments via live connections

- clearer understandable speech if a predefined reaction is possible. Not dependend from the clarity of speech of the guards.

- Possible to be controled from Multiview with custom buttons which address different announcements.

May be used for lots of other applications as well :

- Audio error messages on the GSC. All SystemError/Warning actions may be mapped to an audio message

- Automatically produced audio messages for example by video sensor actions “You are trespassing a forbidden zone …”

The control is done by the action:

ABCPlayFile

with the parameters:

FileID – represents a number of an audio file. The name is automatically created as GSCSOUND_FileID.Wav. The ABC plugin searches for files with that name and plays them.
FileName – represents a name of an audio file. If that parameter is valid FileID is ignored
AutoRepeat – the audio file is played in a loop

The playback of audio files and file loops may be interrupted with the ABC_Disconnect action. The audio files should reside in the GSC home directory.