Friday, July 22, 2005

Taking Pictures with MMAPI

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The Mobile Media API (MMAPI) enables MIDlets to play and record audio and video data. The exact capabilities depend on the device implementation. Currently the only device that supports MMAPI is the Nokia 3650 mobile phone. This article describes how to build a simple camera application using MMAPI.

Tools for MMAPI Development

The first challenge of building an MMAPI application is finding the right tools. The J2ME Wireless Toolkit 2.0 includes support for MIDP 2.0, MMAPI 1.0, and WMA 1.1. At first glance, it looks like this is all you need — but the Nokia 3650 runs MIDP 1.0, not MIDP 2.0. To develop MIDP 1.0 applications, you'll need the 1.0.4 version of the J2ME Wireless Toolkit and an emulator that supports MMAPI.

Sun offers such an emulator, available from the MMAPI home page. While this emulator will allow you to build MMAPI applications, it does not support image capture, so it can't be used to test a camera application.

Nokia has an emulator that does support image capture, part of the Nokia Series 60 MIDP Concept SDK Beta 0.2, available from Forum Nokia, Nokia's developer web site. The file name is nS60_jme_concept_sdk_b0_2_014.zip. Linux developers should be able to use the Nokia Developer's Suite for J2ME, Version 2.0. The following installation instructions apply to Windows only.

Install the Nokia SDK in the \wtklib\devices directory (or copy the Nokia_Series_60_MIDP_Concept_SDK_Beta_0_2 directory there after installation is complete). Next time you run the J2ME Wireless Toolkit, you'll have an additional emulator available, Nokia_Series_60_MIDP_Concept_SDK_Beta_0_2. When this emulator is selected, you can build MMAPI applications and test them as well. The emulator itself looks very much like the Nokia 3650.

MMAPI Device Testing

There's no substitute for testing on real devices. In the long term, many devices will support MMAPI, even though the Nokia 3650 is the only MMAPI device available just now.

There are several ways to deploy a MIDlet on the Nokia 3650. I transfer files via infrared between my laptop and the device. You can also use Bluetooth or do an OTA installation.

Getting a Video Capture Player

The first step in taking pictures (officially called video capture) in a MIDlet is obtaining a Player from the Manager. A special locator, capture://video, indicates that pictures will be captured from the camera using a default image size.

mPlayer = Manager.createPlayer("capture://video");

If the device does not support video capture, a MediaException will be thrown. You can check ahead of time to see whether video capture is supported; if it is, the system property supports.video.capture will be true.

The Player needs to be realized to obtain the resources that are needed to take pictures. If you haven't learned or don't remember what "realized" means, read through Mobile Media API Overview or The J2ME Mobile Media API.

mPlayer.realize();

Showing the Camera Video

The video coming from the camera can be displayed on the screen either as an Item in a Form or as part of a Canvas. A VideoControl makes this possible. To get a VideoControl, just ask the Player for it:

mVideoControl = (VideoControl)
mPlayer.getControl("VideoControl");

If you wish to show the video coming from the camera in a Canvas, initialize the VideoControl, then set the size and location of the video in the Canvas, then make the video visible. The following example (the constructor of a Canvas subclass) shows how to place the video two pixels in from the sides of the Canvas. If the incoming video cannot be placed that way, the constructor tries using the full screen. Finally, it calls setVisible() to make the camera video visible.

public CameraCanvas(SnapperMIDlet midlet,
VideoControl videoControl) {
int width = getWidth();
int height = getHeight();

mSnapperMIDlet = midlet;

videoControl.initDisplayMode(
VideoControl.USE_DIRECT_VIDEO, this);

try {
videoControl.setDisplayLocation(2, 2);
videoControl.setDisplaySize(width - 4, height - 4);
}
catch (MediaException me) {
try { videoControl.setDisplayFullScreen(true); }
catch (MediaException me2) {}
}
videoControl.setVisible(true);
}

Showing the camera video in a Form is slightly different. Instead of calling VideoControl's initDisplayMode() method with USE_DIRECT_VIDEO, use the USE_GUI_PRIMITIVE value instead. On MIDP devices, you'll get back an Item you can place in a Form to be displayed.

Form form = new Form("Camera form");
Item item = (Item)mVideoControl.initDisplayMode(
GUIControl.USE_GUI_PRIMITIVE, null);
form.append(item);

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