（注：本贴为方便自己可快速得知一书中英文段落所讲的主要内容是什么，并非给不懂英文的人看的，当然也可以作一个了解性的阅读）
JMF 是一个应用程序编程接口，它可以让实时的多媒体信息合并到Java 应用程序或者applet小程序中去，让你的应用程序更丰富多彩。
JMF多媒体数据处理模型：
Streaming Media：
实时媒体流的主要特点就是它要求及时的传送和处理。一旦流媒体开始发送，那它就会有一个严格的过期时间。
（原文）A key characteristic of time-based media is that it requires timely delivery
and processing. Once the ßow of media data begins, there are strict timing
deadlines that must be met, both in terms of receiving and presenting the
data. For this reason, time-based media is often referred to as streaming
mediaÑit is delivered in a steady stream that must be received and processed
within a particular timeframe to produce acceptable results.
For example, when a movie is played, if the media data cannot be delivered
quickly enough, there might be odd pauses and delays in playback.
On the other hand, if the data cannot be received and processed quickly
enough, the movie might appear jumpy as data is lost or frames are intentionally
dropped in an attempt to maintain the proper playback rate.
Content Type：
多媒体文件存储的形式、编码格式即content type。
(原文)The format in which the media data is stored is referred to as its content
type. QuickTime, MPEG, and WAV are all examples of content types. Content
type is essentially synonymous with Þle typeÑcontent type is used
because media data is often acquired from sources other than local Þles.
Media Streams:
Media Streams指媒体资源，可以是文件、网络流、捕获的设备流等。
（原文）A media stream is the media data obtained from a local Þle, acquired over
the network, or captured from a camera or microphone. Media streams
often contain multiple channels of data called tracks. For example, a
Quicktime file might contain both an audio track and a video track. Media
streams that contain multiple tracks are often referred to as multiplexed or
complex media streams. Demultiplexing is the process of extracting individual
tracks from a complex media stream.
A trackÕs type identiÞes the kind of data it contains, such as audio or
video. The format of a track deÞnes how the data for the track is structured.
A media stream can be identiÞed by its location and the protocol used to
access it. For example, a URL might be used to describe the location of a
QuickTime Þle on a local or remote system. If the Þle is local, it can be
accessed through the FILE protocol. On the other hand, if itÕs on a web
server, the Þle can be accessed through the HTTP protocol. A media locator
provides a way to identify the location of a media stream when a URL
canÕt be used.
媒体流分类：
媒体流按传送方式分两类：
1：Pull 数据类型，如Pull有拉的含意，有主动捉拉取信息的意思，这种流的传送控制在客户端。
如：http和ftp就是获取pull类型资源的协议，用这些协议都是客户端自主请求与控制是否要获取这些资源，这些资源就可以叫作pull类型数据。
2：Push 数据类型就和上面相反，Push数据资源的发送与控制在服务端，客户端是被动的收取的。
如：RTP（实时传输协议）就是一个Push数据资源收发的协议，类似的有SGI基于媒体的协议也是一个push类型协议，专门用来收发video-on-demand(VOD)。
（原文）Media streams can be categorized according to how the data is delivered:
¥ PullÑdata transfer is initiated and controlled from the client side. For
example, Hypertext Transfer Protocol (HTTP) and FILE are pull
protocols.
¥ PushÑthe server initiates data transfer and controls the flow of data.
For example, Real-time Transport Protocol (RTP) is a push protocol
used for streaming media. Similarly, the SGI MediaBase protocol is a
push protocol used for video-on-demand (VOD).
Media Presentation
媒体的播放：大多数实时媒体数据是audio或者video数据，它们可以通过喇叭或显示器这些设备来播放。
也可发输出到file、network上，有时媒体的输出可以称可data sink。（DataSink也是一个可收发流的实用类）
(原文)Most time-based media is audio or video data that can be presented
through output devices such as speakers and monitors. Such devices are
the most common destination for media data output. Media streams can
also be sent to other destinationsÑfor example, saved to a Þle or transmitted
across the network. An output destination for media data is sometimes
referred to as a data sink.
Presentation Controls
播放控制。媒体流中可以得以control panel来实现与人交互式的控制播放规则。
如：一个play播放一个媒体流，那么可以从play对象实例中得到VisualComponent、ControlPanelComponent组件以给用户提供GUI控制。
While a media stream is being presented, VCR-style presentation controls
are often provided to enable the user to control playback. For example, a
control panel for a movie player might offer buttons for stopping, starting,
fast-forwarding, and rewinding the movie.
Latency
延迟：从用户角度看，开始点击按钮到可以正常观看多媒体流的时间就是延迟。
程序员在对待多媒体异步处理时应该要注意到多媒体 的同步与时延问题。
In many cases, particularly when presenting a media stream that resides
on the network, the presentation of the media stream cannot begin immediately.
The time it takes before presentation can begin is referred to as the
start latency. Users might experience this as a delay between the time that
they click the start button and the time when playback actually starts.
Multimedia presentations often combine several types of time-based
media into a synchronized presentation. For example, background music
might be played during an image slide-show, or animated text might be
synchronized with an audio or video clip. When the presentation of multiple
media streams is synchronized, it is essential to take into account the
start latency of each streamÑotherwise the playback of the different
streams might actually begin at different times.
Presentation Quality
播放质量：影响因素有
1、压缩方法
2、回放系统的处理能力
3、网络可用带宽
The quality of the presentation of a media stream depends on several factors,
including:
¥ The compression scheme used
¥ The processing capability of the playback system
¥ The bandwidth available (for media streams acquired over the
network)
通常要求的质量越高，处理能力和带宽就要求越高。
Traditionally, the higher the quality, the larger the Þle size and the greater
the processing power and bandwidth required. Bandwidth is usually represented
as the number of bits that are transmitted in a certain period of
timeÑthe bit rate.
为了提高video质量，应该增大帧的频率。
To achieve high-quality video presentations, the number of frames displayed
in each period of time (the frame rate) should be as high as possible.
通常movies都是每秒30帧
Usually movies at a frame rate of 30 frames-per-second are considered
indistinguishable from regular TV broadcasts or video tapes.
Media Processing
通常在播放media流之前都要对数据进行一个处理，以更好地展示给users看。
In most instances, the data in a media stream is manipulated before it is
presented to the user. Generally, a series of processing operations occur
before presentation:
1. If the stream is multiplexed, the individual tracks are extracted.//如果一媒体流是多种复合在一起的，则提取出每一个单独的媒体流出来
2. If the individual tracks are compressed, they are decoded.//如果一个单独媒体流是压缩的，则要进行解压
3. If necessary, the tracks are converted to a different format.//如果需要，每一个流还可以转为其它 的格式
4. Effect filters are applied to the decoded tracks (if desired).//也可以增加效果的过滤到解码控制轨道上
The tracks are then delivered to the appropriate output device. If the
media stream is to be stored instead of rendered to an output device, the
processing stages might differ slightly. For example, if you wanted to capture
audio and video from a video camera, process the data, and save it to
a Þle:
1. The audio and video tracks would be captured.
2. Effect filters would be applied to the raw tracks (if desired).
3. The individual tracks would be encoded.
4. The compressed tracks would be multiplexed into a single media
stream.
5. The multiplexed media stream would then be saved to a file.
Demultiplexers and Multiplexers
复合与分支提取
A demultiplexer extracts individual tracks of media data from a multiplexed
media stream. A mutliplexer performs the opposite function, it
takes individual tracks of media data and merges them into a single multiplexed
media stream.
Codecs
编码：压缩与解压、编码与解码
A codec performs media-data compression and decompression. When a
track is encoded, it is converted to a compressed format suitable for storage
or transmission; when it is decoded it is converted to a non-compressed
(raw) format suitable for presentation.
Each codec has certain input formats that it can handle and certain output
formats that it can generate. In some situations, a series of codecs might be
used to convert from one format to another.
Effect Filters
效果过滤器，处理前过滤、处理后过滤
An effect Þlter modiÞes the track data in some way, often to create special
effects such as blur or echo.
Effect Þlters are classiÞed as either pre-processing effects or post-processing
effects, depending on whether they are applied before or after the
codec processes the track. Typically, effect Þlters are applied to uncompressed
(raw) data.
Renderers
renderer展示设备的抽象
A renderer is an abstraction of a presentation device. For audio, the presentation
device is typically the computerÕs hardware audio card that outputs
sound to the speakers. For video, the presentation device is typically
the computer monitor.
Compositing
混合技术，把多个媒体混合到一个单独 的播放设备中
Certain specialized devices support compositing. Compositing time-based
media is the process of combining multiple tracks of data onto a single
presentation medium. For example, overlaying text on a video presentation
is one common form of compositing. Compositing can be done in
either hardware or software. A device that performs compositing can be
abstracted as a renderer that can receive multiple tracks of input data.
Media Capture
Time-based media can be captured from a live source for processing and
playback. For example, audio can be captured from a microphone or a
video capture card can be used to obtain video from a camera. Capturing
can be thought of as the input phase of the standard media processing
model.
A capture device might deliver multiple media streams. For example, a
video camera might deliver both audio and video. These streams might be
captured and manipulated separately or combined into a single, multiplexed
stream that contains both an audio track and a video track.
Capture Devices
capturedeviceInfo类用来得到设备datasource
To capture time-based media you need specialized hardwareÑfor example,
to capture audio from a live source, you need a microphone and an
appropriate audio card. Similarly, capturing a TV broadcast requires a TV
tuner and an appropriate video capture card. Most systems provide a
query mechanism to Þnd out what capture devices are available.
Capture devices can be characterized as either push or pull sources. For
example, a still camera is a pull sourceÑthe user controls when to capture
an image. A microphone is a push sourceÑthe live source continuously
provides a stream of audio.
The format of a captured media stream depends on the processing performed
by the capture device. Some devices do very little processing and
deliver raw, uncompressed data. Other capture devices might deliver the
data in a compressed format.
Capture Controls
Controls are sometimes provided to enable the user to manage the capture
process. For example, a capture control panel might enable the user to
specify the data rate and encoding type for the captured stream and start
and stop the capture process.
扫一扫
198
被折叠的 条评论
为什么被折叠?
到【灌水乐园】发言
