# opal.h File Reference

This file contains a simplified API to the OPAL system. It provides a pure "C" language interface as will as a very simple C++ class and a contrained set of functions for "late binding". More...

`#include <stdlib.h>`

Include dependency graph for opal.h:

Go to the source code of this file.

## Data Structures

struct | OpalParamGeneral
struct | OpalProductDescription
struct | OpalParamProtocol
struct | OpalParamRegistration
struct | OpalStatusRegistration
struct | OpalParamSetUpCall
struct | OpalStatusIncomingCall
struct | OpalParamAnswerCall
struct | OpalStatusMediaStream
struct | OpalParamSetUserData
struct | OpalStatusUserInput
struct | OpalStatusMessageWaiting
struct | OpalStatusLineAppearance
struct | OpalPresenceStatus
struct | OpalInstantMessage
struct | OpalParamRecording
struct | OpalStatusTransferCall
struct | OpalStatusIVR
struct | OpalStatusCallCleared
struct | OpalParamCallCleared
struct | OpalMessage
class | OpalMessagePtr
| Wrapper around the OpalMessage structure. More...
class | OpalContext

## Defines

#define | OPAL_EXPORT
#define | OPAL_C_API_VERSION 29
| Current API version.
#define | OPAL_INITIALISE_FUNCTION "OpalInitialise"
#define | OPAL_SHUTDOWN_FUNCTION "OpalShutDown"
#define | OPAL_GET_MESSAGE_FUNCTION "OpalGetMessage"
#define | OPAL_SEND_MESSAGE_FUNCTION "OpalSendMessage"
#define | OPAL_FREE_MESSAGE_FUNCTION "OpalFreeMessage"
#define | OPAL_PREFIX_H323 "h323"
| H.323 Protocol supported string for OpalInitialise().
#define | OPAL_PREFIX_SIP "sip"
| SIP Protocol supported string for OpalInitialise().
#define | OPAL_PREFIX_IAX2 "iax2"
| IAX2 Protocol supported string for OpalInitialise().
#define | OPAL_PREFIX_PCSS "pc"
| PC sound system supported string for OpalInitialise().
#define | OPAL_PREFIX_LOCAL "local"
| Local endpoint supported string for OpalInitialise().
#define | OPAL_PREFIX_POTS "pots"
| Plain Old Telephone System supported string for OpalInitialise().
#define | OPAL_PREFIX_PSTN "pstn"
| Public Switched Network supported string for OpalInitialise().
#define | OPAL_PREFIX_FAX "fax"
| G.711 fax supported string for OpalInitialise().
#define | OPAL_PREFIX_T38 "t38"
| G.711 fax supported string for OpalInitialise().
#define | OPAL_PREFIX_IVR "ivr"
| Interactive Voice Response supported string for OpalInitialise().
#define | OPAL_PREFIX_IM "im"
| Interactive Voice Response supported string for OpalInitialise().
#define | OPAL_PREFIX_ALL
#define | OPAL_MWI_EVENT_PACKAGE "message-summary"
| Name of SIP event package for Message Waiting events.
#define | OPAL_LINE_APPEARANCE_EVENT_PACKAGE "dialog;sla;ma"
| Name of SIP even package fo rmonitoring call status.

## Typedefs

typedef OpalHandleStruct * | OpalHandle
| Handle to initialised OPAL instance.
typedef OpalMessage | OpalMessage
typedef OpalHandle(OPAL_EXPORT *) | OpalInitialiseFunction (unsigned *version, const char *options)
typedef void(OPAL_EXPORT *) | OpalShutDownFunction (OpalHandle opal)
typedef OpalMessage *(OPAL_EXPORT *) | OpalGetMessageFunction (OpalHandle opal, unsigned timeout)
typedef OpalMessage *(OPAL_EXPORT *) | OpalSendMessageFunction (OpalHandle opal, const OpalMessage *message)
typedef void(OPAL_EXPORT *) | OpalFreeMessageFunction (OpalMessage *message)
typedef int(*) | OpalMediaDataFunction (const char *token, const char *stream, const char *format, void *userData, void *data, int size)
typedef int(*) | OpalMessageAvailableFunction (const OpalMessage *message)
typedef OpalStatusUserInput | OpalParamUserInput

## Enumerations

enum

OpalMessageType {
OpalIndCommandError, OpalCmdSetGeneralParameters, OpalCmdSetProtocolParameters, OpalCmdRegistration,
OpalIndRegistration, OpalCmdSetUpCall, OpalIndIncomingCall, OpalCmdAnswerCall,
OpalCmdClearCall, OpalIndAlerting, OpalIndEstablished, OpalIndUserInput,
OpalIndCallCleared, OpalCmdHoldCall, OpalCmdRetrieveCall, OpalCmdTransferCall,
OpalCmdUserInput, OpalIndMessageWaiting, OpalIndMediaStream, OpalCmdMediaStream,
OpalCmdSetUserData, OpalIndLineAppearance, OpalCmdStartRecording, OpalCmdStopRecording,
OpalIndProceeding, OpalCmdAlerting, OpalIndOnHold, OpalIndOffHold,
OpalIndTransferCall, OpalIndCompletedIVR, OpalCmdAuthorisePresence, OpalCmdSubscribePresence,
OpalCmdSetLocalPresence, OpalIndPresenceChange, OpalCmdSendIM, OpalIndReceiveIM,
OpalIndSentIM, OpalMessageTypeCount
}

enum | OpalSilenceDetectMode { OpalSilenceDetectNoChange, OpalSilenceDetectDisabled, OpalSilenceDetectFixed, OpalSilenceDetectAdaptive }
enum | OpalEchoCancelMode { OpalEchoCancelNoChange, OpalEchoCancelDisabled, OpalEchoCancelEnabled }
enum | OpalMediaDataType { OpalMediaDataNoChange, OpalMediaDataPayloadOnly, OpalMediaDataWithHeader }
enum | OpalMediaTiming { OpalMediaTimingNoChange, OpalMediaTimingSynchronous, OpalMediaTimingAsynchronous, OpalMediaTimingSimulated }
enum | OpalUserInputModes { OpalUserInputDefault, OpalUserInputAsQ931, OpalUserInputAsString, OpalUserInputAsTone, OpalUserInputAsRFC2833, OpalUserInputInBand }
enum | OpalRegistrationStates { OpalRegisterSuccessful, OpalRegisterRemoved, OpalRegisterFailed, OpalRegisterRetrying, OpalRegisterRestored }
enum | OpalMediaStates { OpalMediaStateNoChange, OpalMediaStateOpen, OpalMediaStateClose, OpalMediaStatePause, OpalMediaStateResume }
enum | OpalLineAppearanceStates { OpalLineTerminated, OpalLineTrying, OpalLineProceeding, OpalLineRinging, OpalLineConnected, OpalLineSubcribed, OpalLineUnsubcribed, OpalLineIdle = OpalLineTerminated }
enum | OpalPresenceStates { OpalPresenceAuthRequest = -100, OpalUnknownPresentity = -4, OpalPresenceError, OpalPresenceForbidden, OpalPresenceNone, OpalPresenceUnchanged, OpalPresenceAvailable, OpalPresenceUnavailable }
enum | OpalVideoRecordMixMode { OpalSideBySideLetterbox, OpalSideBySideScaled, OpalStackedPillarbox, OpalStackedScaled }

enum

OpalCallEndReason {
OpalCallEndedByLocalUser, OpalCallEndedByNoAccept, OpalCallEndedByAnswerDenied, OpalCallEndedByRemoteUser,
OpalCallEndedByRefusal, OpalCallEndedByNoAnswer, OpalCallEndedByCallerAbort, OpalCallEndedByTransportFail,
OpalCallEndedByConnectFail, OpalCallEndedByGatekeeper, OpalCallEndedByNoUser, OpalCallEndedByNoBandwidth,
OpalCallEndedByCapabilityExchange, OpalCallEndedByCallForwarded, OpalCallEndedBySecurityDenial, OpalCallEndedByLocalBusy,
OpalCallEndedByLocalCongestion, OpalCallEndedByRemoteBusy, OpalCallEndedByRemoteCongestion, OpalCallEndedByUnreachable,
OpalCallEndedByNoEndPoint, OpalCallEndedByHostOffline, OpalCallEndedByTemporaryFailure, OpalCallEndedByQ931Cause,
OpalCallEndedByDurationLimit, OpalCallEndedByInvalidConferenceID, OpalCallEndedByNoDialTone, OpalCallEndedByNoRingBackTone,
OpalCallEndedByOutOfService, OpalCallEndedByAcceptingCallWaiting, OpalCallEndedWithQ931Code = 0x100
}

## Functions

OpalHandle OPAL_EXPORT | OpalInitialise (unsigned *version, const char *options)
void OPAL_EXPORT | OpalShutDown (OpalHandle opal)
OpalMessage *OPAL_EXPORT | OpalGetMessage (OpalHandle opal, unsigned timeout)
OpalMessage *OPAL_EXPORT | OpalSendMessage (OpalHandle opal, const OpalMessage *message)
void OPAL_EXPORT | OpalFreeMessage (OpalMessage *message)

## Detailed Description

This file contains a simplified API to the OPAL system. It provides a pure "C" language interface as will as a very simple C++ class and a contrained set of functions for "late binding".

It should be noted that the simplified API, is sill not very simple. There are complexities invoved that cannot be avoided. However, this API does remove some issues with the full API such as multi-threading and advanced C++ concepts.

The other major feature of this API is the ability to be easily "late bound" using Windows LoadLibrary() or Unix dlopen() at run time. You may look at the sample code in opal/samples/c_api/main.c for an example of how to do late binding.

Late binding also allows for easier integration of OPAL fucntionality to interpreted languages such as Java, Perl etc. Systems like "swig" may be used to produce interface files for such languages.

To make the above easier, there are only four functions: OpalInitialise(), OpalShutDown(), OpalGetMessage() and OpalSendMessage(). All commands to OPAL and indications back from OPAL are done through the latter two functions.

This API also provides a basic C++ class OpalContext, which may be used for C++ programmers that do not wish to learn the large number of classes in the full API. At the cost of minimal extensibility and control.

## Define Documentation

#define OPAL_C_API_VERSION 29

Current API version.

#define OPAL_EXPORT

#define OPAL_FREE_MESSAGE_FUNCTION "OpalFreeMessage"

String representation of the OpalFreeMessage() which may be used for late binding to the library.

#define OPAL_GET_MESSAGE_FUNCTION "OpalGetMessage"

String representation of the OpalGetMessage() which may be used for late binding to the library.

#define OPAL_INITIALISE_FUNCTION "OpalInitialise"

String representation of the OpalIntialise() which may be used for late binding to the library.

#define OPAL_LINE_APPEARANCE_EVENT_PACKAGE "dialog;sla;ma"

Name of SIP even package fo rmonitoring call status.

#define OPAL_MWI_EVENT_PACKAGE "message-summary"

Name of SIP event package for Message Waiting events.

#define OPAL_PREFIX_ALL

Value:

    OPAL_PREFIX_H323  " " \
                            OPAL_PREFIX_SIP   " " \
                            OPAL_PREFIX_IAX2  " " \
                            OPAL_PREFIX_PCSS  " " \
                            OPAL_PREFIX_LOCAL " " \
                            OPAL_PREFIX_POTS  " " \
                            OPAL_PREFIX_PSTN  " " \
                            OPAL_PREFIX_FAX  " " \
                            OPAL_PREFIX_T38  " " \
                            OPAL_PREFIX_IVR  " " \
                            OPAL_PREFIX_IM

#define OPAL_PREFIX_FAX "fax"

G.711 fax supported string for OpalInitialise().

#define OPAL_PREFIX_H323 "h323"

H.323 Protocol supported string for OpalInitialise().

#define OPAL_PREFIX_IAX2 "iax2"

IAX2 Protocol supported string for OpalInitialise().

#define OPAL_PREFIX_IM "im"

Interactive Voice Response supported string for OpalInitialise().

#define OPAL_PREFIX_IVR "ivr"

Interactive Voice Response supported string for OpalInitialise().

#define OPAL_PREFIX_LOCAL "local"

Local endpoint supported string for OpalInitialise().

#define OPAL_PREFIX_PCSS "pc"

PC sound system supported string for OpalInitialise().

#define OPAL_PREFIX_POTS "pots"

Plain Old Telephone System supported string for OpalInitialise().

#define OPAL_PREFIX_PSTN "pstn"

Public Switched Network supported string for OpalInitialise().

#define OPAL_PREFIX_SIP "sip"

SIP Protocol supported string for OpalInitialise().

#define OPAL_PREFIX_T38 "t38"

G.711 fax supported string for OpalInitialise().

#define OPAL_SEND_MESSAGE_FUNCTION "OpalSendMessage"

Typedef representation of the pointer to the OpalSendMessage() function which may be used for late binding to the library.

#define OPAL_SHUTDOWN_FUNCTION "OpalShutDown"

String representation of the OpalShutDown() which may be used for late binding to the library.

## Typedef Documentation

typedef void(OPAL_EXPORT *) OpalFreeMessageFunction(OpalMessage *message)

Typedef representation of the pointer to the OpalFreeMessage() function which may be used for late binding to the library.

typedef OpalMessage*(OPAL_EXPORT *) OpalGetMessageFunction(OpalHandle opal, unsigned timeout)

Typedef representation of the pointer to the OpalGetMessage() function which may be used for late binding to the library.

typedef struct OpalHandleStruct* OpalHandle

Handle to initialised OPAL instance.

typedef OpalHandle(OPAL_EXPORT *) OpalInitialiseFunction(unsigned *version, const char *options)

Typedef representation of the pointer to the OpalIntialise() function which may be used for late binding to the library.

typedef int(*) OpalMediaDataFunction(const char *token,const char *stream,const char *format,void *userData,void *data,int size)

Function for reading/writing media data. Returns size of data actually read or written, or -1 if there is an error and the media stream should be shut down.

The "write" function, which is taking data from a remote and providing it to the "C" application for writing, should not be assumed to have a one to one correspondence with RTP packets. The OPAL jiter buffer may insert "silence" data for missing or too late packets. In this case the function is called with the size parameter equal to zero. It is up to the application what it does in that circumstance.

Note that this function will be called in the context of different threads so the user must take care of any mutex and synchonisation issues.

typedef struct OpalMessage OpalMessage

typedef int(*) OpalMessageAvailableFunction(const OpalMessage *message)

Function called when a message event becomes available. This function is called before the message is queued for the GetMessage() function.

A return value of zero indicates that the message is not to be passed on to the GetMessage(). A non-zero value will pass the message on.

Note that this function will be called in the context of different threads so the user must take care of any mutex and synchonisation issues. If the user subsequently uses the GetMessage() then the message will have been serialised so that there are no multi-threading issues.

A simple use case would be for this function to send a signal or message to the applications main thread and then return a non-zero value. The main thread would then wake up and get the message using GetMessage.

typedef struct OpalStatusUserInput OpalParamUserInput

User input information for the OpalIndUserInput/OpalCmdUserInput indication.

This is may be returned from the OpalGetMessage() function or provided to the OpalSendMessage() function.

typedef OpalMessage*(OPAL_EXPORT *) OpalSendMessageFunction(OpalHandle opal, const OpalMessage *message)

String representation of the OpalSendMessage() which may be used for late binding to the library.

typedef void(OPAL_EXPORT *) OpalShutDownFunction(OpalHandle opal)

Typedef representation of the pointer to the OpalShutDown() function which may be used for late binding to the library.

## Enumeration Type Documentation

enum OpalCallEndReason

Type code for media stream status/control. This is used by the OpalIndMediaStream indication and OpalCmdMediaStream command in the OpalStatusMediaStream structure.

Enumerator:

  OpalCallEndedByLocalUser |
  OpalCallEndedByNoAccept | Local endpoint application cleared call.
  OpalCallEndedByAnswerDenied | Local endpoint did not accept call OnIncomingCall()=false.
  OpalCallEndedByRemoteUser | Local endpoint declined to answer call.
  OpalCallEndedByRefusal | Remote endpoint application cleared call.
  OpalCallEndedByNoAnswer | Remote endpoint refused call.
  OpalCallEndedByCallerAbort | Remote endpoint did not answer in required time.
  OpalCallEndedByTransportFail | Remote endpoint stopped calling.
  OpalCallEndedByConnectFail | Transport error cleared call.
  OpalCallEndedByGatekeeper | Transport connection failed to establish call.
  OpalCallEndedByNoUser | Gatekeeper has cleared call.
  OpalCallEndedByNoBandwidth | Call failed as could not find user (in GK).
  OpalCallEndedByCapabilityExchange | Call failed as could not get enough bandwidth.
  OpalCallEndedByCallForwarded | Could not find common capabilities.
  OpalCallEndedBySecurityDenial | Call was forwarded using FACILITY message.
  OpalCallEndedByLocalBusy | Call failed a security check and was ended.
  OpalCallEndedByLocalCongestion | Local endpoint busy.
  OpalCallEndedByRemoteBusy | Local endpoint congested.
  OpalCallEndedByRemoteCongestion | Remote endpoint busy.
  OpalCallEndedByUnreachable | Remote endpoint congested.
  OpalCallEndedByNoEndPoint | Could not reach the remote party.
  OpalCallEndedByHostOffline | The remote party is not running an endpoint.
  OpalCallEndedByTemporaryFailure | The remote party host off line.
  OpalCallEndedByQ931Cause | The remote failed temporarily app may retry.
  OpalCallEndedByDurationLimit | The remote ended the call with unmapped Q.931 cause code.
  OpalCallEndedByInvalidConferenceID | Call cleared due to an enforced duration limit.
  OpalCallEndedByNoDialTone | Call cleared due to invalid conference ID.
  OpalCallEndedByNoRingBackTone | Call cleared due to missing dial tone.
  OpalCallEndedByOutOfService | Call cleared due to missing ringback tone.
  OpalCallEndedByAcceptingCallWaiting | Call cleared because the line is out of service,.
  OpalCallEndedWithQ931Code | Call cleared because another call is answered.

enum OpalEchoCancelMode

Type code the echo cancellation algorithm modes. This is used by the OpalCmdSetGeneralParameters command in the OpalParamGeneral structure.

Enumerator:

  OpalEchoCancelNoChange | No change to the echo cancellation mode.
  OpalEchoCancelDisabled | Indicate the echo cancellation is disabled
  OpalEchoCancelEnabled | Indicate the echo cancellation is enabled

enum OpalLineAppearanceStates

Type code for media stream status/control. This is used by the OpalIndMediaStream indication and OpalCmdMediaStream command in the OpalStatusMediaStream structure.

Enumerator:

  OpalLineTerminated | Line has ended a call.
  OpalLineTrying | Line has been siezed.
  OpalLineProceeding | Line is trying to make a call.
  OpalLineRinging | Line is ringing.
  OpalLineConnected | Line is connected.
  OpalLineSubcribed | Line appearance subscription successful.
  OpalLineUnsubcribed | Line appearance unsubscription successful.
  OpalLineIdle |

enum OpalMediaDataType

Type code the media data call back functions data type. This is used by the OpalCmdSetGeneralParameters command in the OpalParamGeneral structure.

This controls if the whole RTP data frame or just the paylaod part is passed to the read/write function.

Enumerator:

  OpalMediaDataNoChange | No change to the media data type.
  OpalMediaDataPayloadOnly | Indicate only the RTP payload is passed to the read/write function
  OpalMediaDataWithHeader | Indicate the whole RTP frame including header is passed to the read/write function

enum OpalMediaStates

Type code for media stream status/control. This is used by the OpalIndMediaStream indication and OpalCmdMediaStream command in the OpalStatusMediaStream structure.

Enumerator:

  OpalMediaStateNoChange | No change to the media stream state.
  OpalMediaStateOpen | Media stream has been opened when indication, or is to be opened when a command.
  OpalMediaStateClose | Media stream has been closed when indication, or is to be closed when a command.
  OpalMediaStatePause | Media stream has been paused when indication, or is to be paused when a command.
  OpalMediaStateResume | Media stream has been paused when indication, or is to be paused when a command.

enum OpalMediaTiming

Timing mode for the media data call back functions data type. This is used by the OpalCmdSetGeneralParameters command in the OpalParamGeneral structure.

This controls if the read/write function is in control of the real time aspects of the media flow. If synchronous then the read/write function is expected to handle the real time "pacing" of the read or written data.

Note this is important both for reads and writes. For example in synchronous mode you cannot simply read from a file and send, or you will likely overrun the remotes buffers. Similarly for writing to a file, the correct operation of the OPAL jitter buffer is dependent on it not being drained too fast by the "write" function.

If marked as asynchroous then the OPAL stack itself will take care of the timing and things like read/write to a disk file will work correctly.

Enumerator:

  OpalMediaTimingNoChange | No change to the media data type.
  OpalMediaTimingSynchronous | Indicate the read/write function is going to handle all real time aspects of the media flow.
  OpalMediaTimingAsynchronous | Indicate the read/write function does not require real time aspects of the media flow.
  OpalMediaTimingSimulated | Indicate the read/write function does not handle the real time aspects of the media flow and they must be simulated by the OPAL library.

enum OpalMessageType

Type code for messages defined by OpalMessage.

Enumerator:

  OpalIndCommandError | An error occurred during a command. This is only returned by OpalSendMessage(). The details of the error are shown in the OpalMessage::m_commandError field.
  OpalCmdSetGeneralParameters | Set general parameters command. This configures global settings in OPAL. See the OpalParamGeneral structure for more information.
  OpalCmdSetProtocolParameters | Set protocol parameters command. This configures settings in OPAL that may be different for each protocol, e.g. SIP & H.323. See the OpalParamProtocol structure for more information.
  OpalCmdRegistration | Register/Unregister command. This initiates a registration or unregistration operation with a protocol dependent server. Currently only for H.323 and SIP. See the OpalParamRegistration structure for more information.
  OpalIndRegistration | Status of registration indication. After the OpalCmdRegistration has initiated a registration, this indication will be returned by the OpalGetMessage() function when the status of the registration changes, e.g. successful registration or communications failure etc. See the OpalStatusRegistration structure for more information.
  OpalCmdSetUpCall | Set up a call command. This starts the outgoing call process. The OpalIndAlerting, OpalIndEstablished and OpalIndCallCleared messages are returned by OpalGetMessage() to indicate the call progress. See the OpalParamSetUpCall structure for more information.
  OpalIndIncomingCall | Incoming call indication. This is returned by the OpalGetMessage() function at any time after listeners are set up via the OpalCmdSetProtocolParameters command. See the OpalStatusIncomingCall structure for more information.
  OpalCmdAnswerCall | Answer call command. After a OpalIndIncomingCall is returned by the OpalGetMessage() function, an application maye indicate that the call is to be answered with this message. The OpalMessage m_callToken field is set to the token returned in OpalIndIncomingCall.
  OpalCmdClearCall | Hang Up call command. After a OpalCmdSetUpCall command is executed or a OpalIndIncomingCall indication is received then this may be used to "hang up" the call. The OpalIndCallCleared is subsequently returned in the OpalGetMessage() when the call has completed its hang up operation. See OpalParamCallCleared structure for more information.
  OpalIndAlerting | Remote is alerting indication. This message is returned in the OpalGetMessage() function when the underlying protocol states the remote telephone is "ringing". See the OpalParamSetUpCall structure for more information.
  OpalIndEstablished | Call is established indication. This message is returned in the OpalGetMessage() function when the remote or local endpont has "answered" the call and there is media flowing. See the OpalParamSetUpCall structure for more information.
  OpalIndUserInput | User input indication. This message is returned in the OpalGetMessage() function when, during a call, user indications (aka DTMF tones) are received. See the OpalStatusUserInput structure for more information.
  OpalIndCallCleared | Call is cleared indication. This message is returned in the OpalGetMessage() function when the call has completed. The OpalMessage m_callToken field indicates which call cleared.
  OpalCmdHoldCall | Place call in a hold state. The OpalMessage m_callToken field is set to the token returned in OpalIndIncomingCall.
  OpalCmdRetrieveCall | Retrieve call from hold state. The OpalMessage m_callToken field is set to the token for the call.
  OpalCmdTransferCall | Transfer a call to another party. This starts the outgoing call process for the other party. See the OpalParamSetUpCall structure for more information.
  OpalCmdUserInput | User input command. This sends specified user input to the remote connection. See the OpalStatusUserInput structure for more information.
  OpalIndMessageWaiting | Message Waiting indication. This message is returned in the OpalGetMessage() function when an MWI is received on any of the supported protocols.
  OpalIndMediaStream | A media stream has started/stopped. This message is returned in the OpalGetMessage() function when a media stream is started or stopped. See the OpalStatusMediaStream structure for more information.
  OpalCmdMediaStream | Execute control on a media stream. See the OpalStatusMediaStream structure for more information.
  OpalCmdSetUserData | Set the user data field associated with a call
  OpalIndLineAppearance | Line Appearance indication. This message is returned in the OpalGetMessage() function when any of the supported protocols indicate that the state of a "line" has changed, e.g. free, busy, on hold etc.
  OpalCmdStartRecording | Start recording an active call. See the OpalParamRecording structure for more information.
  OpalCmdStopRecording | Stop recording an active call. Only the m_callToken field of the OpalMessage union is used.

  OpalIndProceeding

  Call has been accepted by remote. This message is returned in the OpalGetMessage() function when the underlying protocol states the remote endpoint acknowledged that it will route the call. This is distinct from OpalIndAlerting in that it is not known at this time if anything is ringing. This indication may be used to distinguish between "transport" level error, in which case another host may be tried, and that the responsibility for finalising the call has moved "upstream". See the OpalParamSetUpCall structure for more information.

  OpalCmdAlerting | Send an indication to the remote that we are "ringing". The OpalMessage m_callToken field indicates which call is alerting.
  OpalIndOnHold | Indicate a call has been placed on hold by remote. This message is returned in the OpalGetMessage() function.
  OpalIndOffHold | Indicate a call has been retrieved from hold by remote. This message is returned in the OpalGetMessage() function.
  OpalIndTransferCall | Status of transfer operation that is under way. This message is returned in the OpalGetMessage() function. See the OpalStatusTransferCall structure for more information.
  OpalIndCompletedIVR | Indicates completion of the IVR (VXML) script. This message is returned in the OpalGetMessage() function. See the OpalStatusIVR structure for more information.
  OpalCmdAuthorisePresence | Permit or deny authority for the remote presentity to view the presence state of a local presentity. See the OpalPresenceStatus structure for more information.
  OpalCmdSubscribePresence | Subscribe to the change in presence state for a presentity. See the OpalPresenceStatus structure for more information.
  OpalCmdSetLocalPresence | Set, and publish, the local presence state. See the OpalPresenceStatus structure for more information.
  OpalIndPresenceChange | Indicates a change the the presence state for a given presentity. This message is returned in the OpalGetMessage() function. See the OpalPresenceStatus structure for more information.
  OpalCmdSendIM | Send an Instant Message. See the OpalInstantMessage structure for more information.
  OpalIndReceiveIM | Indicates receipt of an instant message. This message is returned in the OpalGetMessage() function. See the OpalInstantMessage structure for more information.
  OpalIndSentIM | Get indication of the disposition of a sent instant message. This message is returned in the OpalGetMessage() function. See the OpalInstantMessage structure for more information.
  OpalMessageTypeCount |

enum OpalPresenceStates

Type code for presence states. This is used by the OpalPresenceStatus structure.

Enumerator:

  OpalPresenceAuthRequest | Authorisation to view a users state is required.
  OpalUnknownPresentity | Presentity does not exist.
  OpalPresenceError | Something bad happened.
  OpalPresenceForbidden | Access to presence information was specifically forbidden.
  OpalPresenceNone | No presence status - not the same as Unavailable or Away.
  OpalPresenceUnchanged | State has not changed from last time.
  OpalPresenceAvailable | User has a presence and is available to be contacted.
  OpalPresenceUnavailable | User has a presence, but is cannot be contacted.

enum OpalRegistrationStates

Type code for media stream status/control. This is used by the OpalIndRegistration indication in the OpalStatusRegistration structure.

Enumerator:

  OpalRegisterSuccessful | Successfully registered.
  OpalRegisterRemoved | Successfully unregistered. Note that the m_error field may be non-null if an error occurred during unregistration, however the unregistration will "complete" as far as the local endpoint is concerned and no more registration retries are made.
  OpalRegisterFailed | Registration has failed. The m_error field of the OpalStatusRegistration structure will contain more details.
  OpalRegisterRetrying | Registrar/Gatekeeper has gone offline and a failed retry has been executed.
  OpalRegisterRestored | Registration has been restored after a succesfull retry.

enum OpalSilenceDetectMode

Type code the silence detect algorithm modes. This is used by the OpalCmdSetGeneralParameters command in the OpalParamGeneral structure.

Enumerator:

  OpalSilenceDetectNoChange | No change to the silence detect mode.
  OpalSilenceDetectDisabled | Indicate silence detect is disabled
  OpalSilenceDetectFixed | Indicate silence detect uses a fixed threshold
  OpalSilenceDetectAdaptive | Indicate silence detect uses an adaptive threashold

enum OpalUserInputModes

Type code for controlling the mode in which user input (DTMF) is sent. This is used by the OpalCmdSetProtocolParameters command in the OpalParamProtocol structure.

Enumerator:

  OpalUserInputDefault | Default mode for protocol.
  OpalUserInputAsQ931 | Use Q.931 Information Elements (H.323 only).
  OpalUserInputAsString | Use arbitrary strings (H.245 string, or INFO dtmf).
  OpalUserInputAsTone | Use DTMF specific names (H.245 signal, or INFO dtmf-relay).
  OpalUserInputAsRFC2833 | Use RFC 2833 for DTMF only.
  OpalUserInputInBand | Use in-band generated audio tones for DTMF.

enum OpalVideoRecordMixMode

Type of mixing for video when recording. This is used by the OpalCmdStartRecording command in the OpalParamRecording structure.

Enumerator:

  OpalSideBySideLetterbox | Two images side by side with black bars top and bottom. It is expected that the input frames and output are all the same aspect ratio, e.g. 4:3. Works well if inputs are QCIF and output is CIF for example.
  OpalSideBySideScaled | Two images side by side, scaled to fit halves of output frame. It is expected that the output frame be double the width of the input data to maintain aspect ratio. e.g. for CIF inputs, output would be 704x288.
  OpalStackedPillarbox | Two images, one on top of the other with black bars down the sides. It is expected that the input frames and output are all the same aspect ratio, e.g. 4:3. Works well if inputs are QCIF and output is CIF for example.
  OpalStackedScaled | Two images, one on top of the other, scaled to fit halves of output frame. It is expected that the output frame be double the height of the input data to maintain aspect ratio. e.g. for CIF inputs, output would be 352x576.

## Function Documentation

void OPAL_EXPORT OpalFreeMessage | ( | OpalMessage * | message | ) |

Free memeory in message the OPAL system has sent. The parameter must be the message returned by OpalGetMessage() or OpalSendMessage().

OpalMessage* OPAL_EXPORT OpalGetMessage | ( | OpalHandle | opal,
|  | unsigned | timeout |
| ) |  |  |

Get a message from the OPAL system. The first parameter must be the handle returned by OpalInitialise(). The second parameter is a timeout in milliseconds. NULL is returned if a timeout occurs. A value of UINT_MAX will wait forever for a message.

The returned message must be disposed of by a call to OpalFreeMessage().

The OPAL system will serialise all messages returned from this function to avoid any multi-threading issues. If the application wishes to avoid even this small delay, there is a callback function that may be configured that is not thread safe but may be used to get the messages as soon as they are generated. See OpalCmdSetGeneralParameters.

Note if OpalShutDown() is called from a different thread then this function will break from its block and return NULL.

Example: `OpalMessage * message;`

`while ((message = OpalGetMessage(hOPAL, timeout)) != NULL) { switch (message->m_type) { case OpalIndRegistration : HandleRegistration(message); break; case OpalIndIncomingCall : Ring(message); break; case OpalIndCallCleared : HandleHangUp(message); break; } FreeMessageFunction(message); }`

OpalHandle OPAL_EXPORT OpalInitialise | ( | unsigned * | version,
|  | const char * | options |
| ) |  |  |

Initialise the OPAL system, returning a "handle" to the system that must be used in other calls to OPAL.

The version parameter indicates the version of the API being used by the caller. It should always be set to the constant OPAL_C_API_VERSION. On return the library will indicate the API version it supports, if it is lower than that provided by the application.

The C string options are space separated tokens indicating various options to be enabled, for example the protocols to be available. NULL or an empty string will load all available protocols. The current protocol tokens are: `sip sips h323 h323s iax2 pc local pots pstn ivr` The above protocols are in priority order, so if a protocol is not explicitly in the address, then the first one of the opposite "category" s used. There are two categories, network protocols (sip, h323, iax & pstn) and non-network protocols (pc, local, pots & ivr).

Additional options are:

TraceLevel=1 | Level for tracing.
TraceAppend | Append to the trace file.
TraceFile="name" | Set the filename for trace output. Note quotes are required if spaces are in filename.

It should also be noted that there must not be spaces around the '=' sign in the above options.

If NULL is returned then an initialisation error occurred. This can only really occur if the user specifies prefixes which are not supported by the library.

Example: `OpalHandle hOPAL; unsigned version;`

`version = OPAL_C_API_VERSION; if ((hOPAL = OpalInitialise(&version, OPAL_PREFIX_H323 " " OPAL_PREFIX_SIP " " OPAL_PREFIX_IAX2 " " OPAL_PREFIX_PCSS " TraceLevel=4")) == NULL) { fputs("Could not initialise OPAL\n", stderr); return false; }`

OpalMessage* OPAL_EXPORT OpalSendMessage | ( | OpalHandle | opal,
|  | const OpalMessage * | message |
| ) |  |  |

Send a message to the OPAL system. The first parameter must be the handle returned by OpalInitialise(). The second parameter is a constructed message which is a command to the OPAL system.

Within the command message, generally a NULL or empty string, or zero value for integral types, indicates the particular parameter is to be ignored. Documentation on individiual messages will indicate which are mandatory.

The return value is another message which will have a type of OpalIndCommandError if an error occurs. The OpalMessage::m_commandError field will contain a string indicating the error that occurred.

If successful, the the type of the message is the same as the command type. The message fields in the return will generally be set to the previous value for the field, where relevant. For example in the OpalCmdSetGeneralParameters command the OpalParamGeneral::m_stunServer would contain the STUN server name prior to the command.

A NULL is only returned if the either OpalHandle or OpalMessage parameters is NULL.

The returned message must be disposed of by a call to OpalFreeMessage().

Example: `void SendCommand(OpalMessage * command) { OpalMessage * response; if ((response = OpalSendMessage(hOPAL, command)) == NULL) { puts("OPAL not initialised."); else if (response->m_type != OpalIndCommandError) HandleResponse(response); else if (response->m_param.m_commandError == NULL || *response->m_param.m_commandError == '\0') puts("OPAL error."); else printf("OPAL error: %s\n", response->m_param.m_commandError);`

`FreeMessageFunction(response); }`

void OPAL_EXPORT OpalShutDown | ( | OpalHandle | opal | ) |

Shut down and clean up all resource used by the OPAL system. The parameter must be the handle returned by OpalInitialise().

Example: `OpalShutDown(hOPAL);`