Multimedia Framework API
1.0 References[1] Software Architecture Document, Version 1.1 Revision 1.4, LiMo Foundation, 11 September 20072.0 OverviewThe Multimedia Framework is designed to provide easy to use services for developing multimedia applications based on an embedded Linux platform.The Multimedia Framework API reference has defined APIs to support the functions below:
2.1 Architecture DesignThe multimedia framework can be divided into three parts:
Multimedia Architecture 2.2 Multimedia Framework LibrariesThe Multimedia Framework consists of five libraries to provide high-level APIs for multimedia applications. The Attributes library is a common module for manipulating the attributes of each library. The others provide functions for doing multimedia tasks.2.2.1 Player LibraryThe Player Library provides various functions for a multimedia application to implement playback of media contents. An application can play different formats of audio and audio/video files. File formats could include MP3, OGG, MP4, 3GP and others. The Player Library provides a consistent interface for playing different formats by hiding the creation/construction of various streaming elements from the application. This should make the application coding simpler and faster.The Player Library provides functions that play the media, stop play-back, and pause/resume playback. An application can seek to any desired location of the media by time, video-frame or percentage of file. At the same time, an application can request the current position which can be utilized to implement elapsed time display. Application can utilize trick-mode APIs to implement fast-forward & fast-rewind. The Player Library also facilitates extraction of metadata information like album name, author, track name etc. Controlling the volume is also possible using the Player Library. 2.2.2 Camcorder LibraryThe Camcorder Library provides various functions for multimedia applications to implement recording of various media contents. An application can record audio and audio/video into local files. File formats could include MP3, AAC, MP4 etc. An application can also capture images into files in JPEG or other image formats.This library provides a similar interface for audio recording, audio/video recording and image capture. The type of encoding to be used for audio, video or image, and the file format can be selected by the application. An application can also implement preview while simultaneously recording or capturing the image. Image capture could be still-shot or multi-shot where the interval between captures could be defined by the application. The library provides all the standard camcorder controls such as white-balance, color-tone, optical-filters, day/night mode, flip etc. An application can query the display's orientation, get/set scale parameters, and the width/height of the display. Similarly, an application can also determine the sound device's capabilities such as sample rate, number of audio channels etc. 2.2.3 Sound LibraryThe Sound Library provides functions to manage the sound system. An application can increase/decrease volume and, mute/unmute using this library. An application can control audio input devices like microphones, hands-free devices, etc. It can also control audio output devices such as ear-phones, speaker-phones, hands-free devices, etc.2.2.4 Image LibraryThe Image Library provides functions to convert images into various formats. An application can read files encoded in JPEG, PNG, etc. and convert them into alternate image formats. An application can also obtain the decoded raw image data using this library.2.2.5 Attributes LibraryThe Attributes Library provides functions for manipulating the attributes of multimedia handles such as player, camcorder, image, etc. Attributes can be of various types such as integer, float, string or data (void*). An application can use get/set functions to set values for various attributes. For an attribute of type integer, the application could also set the range of values that this attribute can assume. For example, a player could have a sampling-rate attribute and the application could define specific valid values such as 22050, 44100, etc. for this attribute.2.3 How to Use the Multimedia FrameworkEach multimedia function can be manipulated with the handle. The handle is obtained by calling the appropriate create function such as MMPlayerCreate for player, MMCamcorderCreate for Camcorder, MMImageCreateFromFile for image. These functions each create an instance and return a handle. The handle is passed to other APIs to achieve the desired functionality.For a player, the sequence of function calls is indicated below:
Attributes that are necessary for the initialization of the player/camcorder instances are set before the instance initialization. Changing these attributes after initialization does not have any effect. For example, the codec setting to be used for encoding cannot be changed after initialization. The attributes that determine the controls or properties of the instance can be changed after initialization. For example, the white-balance control of the camcorder. 3.0 Industry StandardNone4.0 External API DocumentsNone5.0 Plug-in Extension Point InterfaceNone6.0 Other InterfacesNone7.0 Other NotesNone
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