|
One important capability of Adobe® Flash® Player and Adobe® AIR™
is the ability to display and manipulate video information with
ActionScript in the same way that you can manipulate other visual
content such as images, animation, text, and so on. When you create
a Flash Video (FLV) file in Adobe Flash CS4 Professional, you have
the option to select a skin that includes common playback controls.
However, there is no reason you need to limit yourself to the options available.
Using ActionScript, you have fine-tuned control over loading, displaying,
and playback of video—meaning you could create your own video player
skin, or use your video in any less traditional way that you want.
Working with video in ActionScript involves working with a combination
of several classes:
-
Video class
: The classic video content
box on the Stage is an instance of the Video class. The Video class
is a display object, so it can be manipulated using the same techniques
that can be applied to other display objects, such as positioning,
applying transformations, applying filters and blending modes, and
so forth.
-
StageVideo class
: The Video class
typically uses software decoding and rendering. When GPU hardware
acceleration is available on a device, your application can take
best advantage of hardware accelerated presentation by switching
to the StageVideo class. The StageVideo API includes a set of events that
tell your code when to switch between StageVideo and Video objects. Stage
video imposes some minor restrictions on video playback. If your
application accepts those limitations, implement the StageVideo
API. See
Guidelines and limitations
.
-
NetStream class
: When you’re loading
a video file to be controlled by ActionScript, a NetStream instance
represents the source of the video content—in this case, a stream
of video data. Using a NetStream instance also involves using a
NetConnection object, which is the connection to the video file—like the
tunnel that the video data is fed through.
-
Camera class
: When you’re working
with video data from a camera connected to the user’s computer,
a Camera instance represents the source of the video content—the
user’s camera and the video data it makes available. New in Flash
Player 11.4 and AIR 3.4, you can use a camera to feed StageVideo.
When you’re loading external video, you can load the file from
a standard web server for progressive download, or you can work
with streaming video delivered by a specialized server such as Adobe’s Flash® Media Server.
Important concepts and terms
-
Cue point
-
A marker that can be placed at a specific moment in time
in a video file, for example to act like a bookmark for locating
that point in time, or to provide additional data that is associated
with that moment in time.
-
Encoding
-
The process of taking video data in one format and converting
it to another video data format; for example, taking a high-resolution
source video and converting it to a format that’s suitable for Internet
delivery.
-
Frame
-
A single segment of video information; each frame is like
a still image representing a snapshot of a moment in time. By playing
frames in sequence at high speed, the illusion of motion is created.
-
Keyframe
-
A video frame which contains the full information for the
frame. Other frames that follow a keyframe only contain information
about how they differ from the keyframe, rather than containing
the full frame’s worth of information.
-
Metadata
-
Information about a video file that is embedded within the
video file and retrieved when the video has loaded.
-
Progressive download
-
When a video file is delivered from a standard web server,
the video data is loaded using progressive download, meaning the
video information loads in sequence. This has the benefit that the
video can begin playing before the entire file is downloaded; however,
it prevents you from jumping ahead to a part of the video that hasn’t
loaded.
-
Streaming
-
As an alternative to progressive download, a special video
server can be used to deliver video over the Internet using a technique
known as streaming (sometimes called “true streaming”). With streaming,
the viewer’s computer never downloads the entire video at one time.
To speed up download times, at any moment the computer only needs
a portion of the total video information. Because a special server
controls the delivery of the video content, any part of the video
can be accessed at any time, rather than needing to wait for it
to download before accessing it.
|
|
|
