Rendering Multimedia Content - Beginning Java ME Platform - page 477

Once initMediaPlayer does its work, control returns to playFromResource , which
invokes either configViewSound or configViewVideo to do any additional postconfiguration
of the user interface before starting the media playback. The configViewSound method
does nothing; it's simply a placeholder. You might want to experiment with the code and
create various Control subclasses on the player field here, such as a VolumeControl .
configViewVideo , however, must do a little work; it creates another Command instance
that lets you trigger a video capture and adds it to the Form instance before creating the
VideoControl instance. The resulting VideoControl provides the method with an Item
instance to add to the Form . Finally, the method creates a second additional empty
ImageItem instance that the MIDlet uses to display the image you capture when you
select the Capture option.
The playFromResource method then starts the newly created Player instance and sets
the current Viewable instance to the viewerDisplayable before returning control to the
player thread's run method. At this point in the MIDlet execution, the MMAPI renders the
media you selected, while the player thread blocks on this waiting for you to select the
Capture option.
Capturing Images
The VideoControl instance that the MIDlet stores in the videoControl field can capture a
snapshot once its Player instance has begun playback, although it's inadvisable to do so
on the main thread, because that can stall either the MIDlet UI or the MMAPI itself. By
using the MIDlet instance itself as an explicit lock via the Java synchronized keyword and
the Object method notify , the MIDlet can signal from the UI thread to the player thread
that you want to capture a frame. In addition, using the synchronized keyword ensures
that you can't trigger a capture while the application is performing a capture, which is
probably an error anyway.
Once the Java VM uses notify / synchronized to kick the player thread to capture a
frame, the player thread performs the capture by invoking the videoControl 's getSnapshot
method, specifying the default encoding. At this point, the player has a byte[] of the cap-
tured image data; the code just uses the data to set the other image on the Form to display
the image you captured.
Another thing you might want to do with image data that your application has cap-
tured is to share it with someone else. You could do that by changing the MMSSender class I
show you in Chapter 14 to take an optional byte[] of encoded image data, as you see in
Listing 16-18, and using the new MMSSender method that Listing 16-18 defines.