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}}} = PJMEDIA Audio Device API = '''Table of Contents''' [[PageOutline(2-3,,inline)]] The '''PJMEDIA Audio Device API''' is a new sound device abstraction API/library in PJMEDIA, introduced in PJSIP version 1.1, deprecating the [http://www.pjsip.org/pjmedia/docs/html/group__PJMED__SND.htm existing sound device API]. [[BR]] == Background == The '''PJMEDIA Audio Device API''' was introduced as part of the implementation of [wiki:Nokia_APS_VAS_Direct APS-Direct] implementation in PJSIP version 1.1. During the design and implementation of [wiki:Nokia_APS_VAS_Direct APS-Direct] project, it was clear that the [http://www.pjsip.org/pjmedia/docs/html/group__PJMED__SND.htm existing sound device API] lacks many features that are needed to support the project. We had the choice to either patch the existing API with new features that are specific to Nokia APS, and potentially break existing applications anyway, or design a new sound device API to support all these new features as well as future enhancements, while providing some support for the old sound API and a clear migration path to the new API. [[BR]] == Features == The new audio device API contains the following major features. '''Forward compatibility:''' :: The new API has been designed to be extensible, it will support new API's as well as new features that may be introduced in the future without breaking compatibility with applications that use this API as well as compatibility with existing device implementations. '''Backward compatibility:''' :: While this is a completely new audio API and implementation, compatibility layers have been implemented for existing applications or sound device implementations that make use of the old API. More will be explained later. '''Device capabilities:''' :: At the heart of the API is device capabilities management, where all possible audio capabilities of audio devices should be able to be handled in a generic manner. With this framework, new capabilities that may be discovered in the future can be handled in manner without breaking existing applications. '''Built-in features:''' :: The device capabilities framework enables applications to use audio features built-in in the device, such as echo cancellation, built-in codecs, audio routing, and volume control. '''Codec support:''' :: Some audio devices such as Nokia/Symbian Audio Proxy Server (APS) and Nokia VoIP Audio Services (VAS) support built-in hardware audio codecs (e.g. G.729, iLBC, and AMR), and this feature is supported by the new audio device API. '''Multiple backends:''' :: The new API supports multiple audio backends (may be called ''factories'' or ''drivers'' in the code) to be active simultaneously, and audio backends may be added or removed during run-time. [[BR]] == Migration Path == === Common Tasks === 1. The Audio Device API is implemented as a new (static) library called '''pjmedia-audiodev''', under '''pjmedia''' directory. Please add this library into link specifications of your application. === Ported Devices === The following audio device backends have been ported to the new API: - !PortAudio - Windows Multimedia/WMME - Nokia APS for S60 - Symbian MMF/MDA === Compatibility settings === Two compile-time macros have been introduced to enable or disable the compatibility layers. The default values for the settings enable existing application to work unchanged, '''{{{PJMEDIA_HAS_LEGACY_SOUND_API}}}''' :: Location: pjmedia/config.h[[BR]] Default: 1[[BR]] Purpose: to enable application to access the sound device using the old (sound.h) API.[[BR]] Description: This macro controls whether the legacy sound device API is to be supported, for applications that still use the old sound device API (sound.h). If this macro is set to non-zero, the sound_legacy.c will be included in the compilation. The sound_legacy.c is an implementation of old sound device (sound.h) using the new Audio Device API. '''{{{PJMEDIA_AUDIO_DEV_HAS_LEGACY_DEVICE}}}''' :: Location: pjmedia-audiodev/config.h[[BR]] Default: 0[[BR]] Purpose: to enable sound device implemented using the old API to be accessed using the new API.[[BR]] Description: This setting controls whether the Audio Device API should support device implementation that is based on the old sound device API (sound.h). === Migration strategy === Use the following checklist to select which setting is appropriate for your build. 1. I use sound devices provided by PJMEDIA (I don't have my own sound device implementation), or I have ported my sound device implementation to the new API a. I haven't changed my application to use the new API - the default settings should be okay a. I have changed my application to use the new API - the default settings should be okay. You may disable {{{PJMEDIA_HAS_LEGACY_SOUND_API}}} to make sure that all codes are using the new API (as well as to reduce footprint slightly). 1. I have my own sound device implementation, based on old API a. I haven't changed my application to use the new API - disable both {{{PJMEDIA_HAS_LEGACY_SOUND_API}}} and {{{PJMEDIA_AUDIO_DEV_HAS_LEGACY_DEVICE}}}. Note that with this setting, you cannot use the new API to access your device implementation. PJSUA-LIB will not work either as PJSUA-LIB uses the new API. a. I have changed my application to use the new API - disable {{{PJMEDIA_HAS_LEGACY_SOUND_API}}} and enable {{{PJMEDIA_AUDIO_DEV_HAS_LEGACY_DEVICE}}}. [[BR]] == Changes == As stated above, existing applications should build fine with the new changes. However, it will still be beneficial to port the application to use the new API since the old sound API has been deprecated, and also to make use of the new features in the new Audio Device API. === Default device convention === Old API:: Value -1 is used throughout to denote default device New API:: Default devices are encoded with the following constants: - PJMEDIA_AUD_DEFAULT_CAPTURE_DEV (-1) is not used to denote default capture device, and - PJMEDIA_AUD_DEFAULT_PLAYBACK_DEV (-2) for default playback device. Applications using the old convention is expected to work with the new API. === Configuring AEC with the sound port === #ec Old API:: The echo cancellation is usually configured after the sound port is created, by using {{{pjmedia_snd_port_set_ec()}}}. New API:: The semantic of {{{pjmedia_snd_port_set_ec()}}} API has been changed to ''to change the settings of the AEC'' rather than ''to enable AEC''. With the new API, the best way to configure AEC is to set the EC parameters in the {{{pjmedia_aud_param}}} when creating the sound device or sound device port, e.g.: {{{ pjmedia_aud_param param; .. param.flags |= (PJMEDIA_AUD_DEV_CAP_EC | PJMEDIA_AUD_DEV_CAP_EC_TAIL); param.ec_enabled = PJ_TRUE; param.ec_tail_ms = ..; .. pjmedia_snd_port_create2(pool, ¶m, &snd_port); }}} If {{{pjmedia_snd_port_set_ec()}}} is called after the sound port is opened, the behavior is as follows: - if the device supports (hardware) AEC, as indicated by device capabilities, then the sound port will forward the change request to the device. The device may or may not support the request to change AEC parameters after the device is opened. - if software AEC is being used (for devices that don't support AEC), this will change the setting of the software AEC. Effectively this resembles the old behavior of the API. === PJSUA-LIB applications === PJSUA-LIB applications that only make use of the API in {{{}}} should require minimum changes. 1. Add '''pjmedia-audiodev''' library to the link specifications of your application. 2. '''Latency''' setting. Old code may set latency directly accessing PJMEDIA API: {{{ pjmedia_snd_set_latency(rec_latency, play_latency); }}} Now latency setting is part of PJSUA-LIB API: {{{ pjsua_media_config media_cfg; .. media_cfg.snd_rec_latency = ..; media_cfg.snd_play_latency = ..; }}} Call to {{{pjmedia_snd_set_latency()}}} will only set the latency if the sound device is opened using the old API. 3. '''New API:''' - {{{pjsua_snd_is_active()}}}: to query if sound device is currently active - {{{pjsua_snd_set_setting()}}}/{{{pjsua_snd_get_setting()}}}: to set or retrieve the value of sound device capability (example of capabilities are audio routing and volume control) === PJMEDIA applications === Below are list of changes for applications that directly uses the old sound API as declared in {{{}}}. 1. Change the header file to include. Old code: {{{ #include }}} New code: {{{ #include }}} 2. Add '''pjmedia-audiodev''' library to the link specifications of your application. 3. Sound device subsystem startup and shutdown. Old code: {{{ pjmedia_snd_init(pf); ... pjmedia_snd_deinit(); }}} New code: {{{ pjmedia_aud_subsys_init(pf); ... pjmedia_aud_subsys_shutdown(); }}} 4. Device enumeration. Old code: {{{ unsigned i, dev_count; dev_count = pjmedia_snd_get_dev_count(); for (i=0; i
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