移动媒体api外文翻译(编辑修改稿)

移动媒体api外文翻译(编辑修改稿)内容摘要：

the JCP. As stated earlier, this RI is bundled with the Java ME Wireless Toolkit supplied by Sun. Different device manufacturers supply their own implementations patible with the TCK. All devices that support MIDP automatically support the scaleddown version of MMAPI. Many devices support the full version as an optional package. Table 11 gives a prehensive list of devices that support MMAPI as an optional package. Summary This chapter introduced MMAPI, an optional package for the development of MIDlets that have embedded audio/video capabilities. MMAPI provides these capabilities by defining a specification that is protocol and format agnostic, thereby increasing general acceptance and uptake. This has made MMAPI very popular and more and more devices support it. With this introduction to MMAPI’ s features and requirements plete, the next chapter addresses the MMAPI architecture, which is key to understanding and using MMAPI. The MMAPI specification was created to cater to the widest range of multimedia options, and this is reflected in its architecture. It supports the most basic audio functions in a constrained device and at the same time provides ways to handle advanced multimedia data on more capable devices. MMAPI supports data from various sources and in various formats. MMAPI’ s protocol and format agnostic characteristic is achieved by a welldesigned, highlevel interface. This chapter explains how the MMAPI specification achieves this aim of platform and format neutrality. You’ ll bee familiar with the details of its architecture and the highlevel objects that make it a successful specification. You’ ll see how the subset of MMAPI present in MIDP differs from the overall specification. Finally, the chapter covers several small details of the MMAPI architecture, such as feature sets and security scenarios, to help you better understand and use MMAPI. Understanding Players and DataSources MIDlets can receive multimedia data from a variety of sources: located in aMIDlet’ s JAR file。 e over the work via several different protocols (HTTP, RTP)。 sourced from the device’ s record store on which the MIDlet is running。 and even e from user input via an audio or video capture device. In short, not only can this data be sourced from different locations, but also these locations can be accessed using any number of present or future protocols. At a conceptual level, MMAPI can handle all such locations and protocols without getting tied down to a specific protocol or location. After data has been sourced, MMAPI should be able to process this data and make it available for rendering on the device. Processing multimedia data is inherently plex and requires the API to not only understand the data but decode it as well. Rendering the data and providing controls to manipulate it further plicates the process. Because MMAPI is a highlevel interface,it doesn’ t mandate any specific dataprocessing functionality, besides a very low level of audio handling. To achieve this neutrality with regard to sources of multimedia data and processing, MMAPI encapsulates these concepts into two highlevel objects: Player and DataSource. Whereas Player is an interface that deals with processing and playing multimedia data, DataSource is an abstract class that encapsulates the task of data location and retrieval while maintaining protocol independence. The Player interface is defined in the package, and DataSource is defined in the package. Player and DataSource work together to provide multimedia capability in a device. A Player instance parses data supplied to it from a DataSource instance. The Player may then render this data on the device and provide controls to manipulate it. For example, an audio Player can provide volume controls to increase or decrease the playback volume. DataSource Basics The DataSource class provides access to multimedia files by locating and opening a connection to them. You may not need to use this class directly, unless you are going to create a DataSource for a custom protocol or location. The MMAPI implementation provided by the device that you are targeting your MIDlet to will provide enough DataSource instances to satisfy most requirements. Each DataSource is posed of one or more streams, known as a SourceStream (an interface in the package). A SourceStream is used to abstract a single stream of media data. Conceptually, multimedia data may be posed of several streams. For example, video files may be broken down into separate streams, one for audio and one for video. Thus, each individual stream can be acted on, independently of the other stream, thereby giving greater control than is possible otherwise. Most DataSource instances are posed of a single SourceStream. A SourceStream also has the advantage of being randomly seekable, because it provides the seek(long where) method. This is an important consideration for multimedia data because it allows you to render this data from an arbitrary position. Of course, a particular stream may not support random seek operations, and this is reflected by the getSeekType() meth。