精通Android多媒体开发：图像、音频和视频应用指南

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"《Apress.Pro.Android.Media.Dec.2010》是一本专注于Android多媒体开发的专业书籍，全英文原版未删减。作者Shawn Van Every深入探讨了Android SDK中的多媒体功能，旨在帮助读者创建动态的移动应用程序，涵盖了智能手机和平板电脑上的图形、音乐、视频和丰富媒体应用的开发。书中的内容分为三个主要部分，分别针对图像、音频和视频进行详细讲解，并涉及利用Web服务查找和分享多媒体内容。" 这本书详细介绍了如何利用Android的媒体APIs来构建创新的应用程序。在图像处理方面，它会引导读者了解如何在Android平台上进行图形绘制、图像显示和操作，包括图片的加载、显示和编辑等技术。此外，书中还可能涉及了图像特效和动画的实现，这对于创建引人入胜的用户界面至关重要。音频部分，作者Shawn Van Every深入讲解了Android的音频处理框架，包括音频播放、录音、音效处理和音频流的管理。读者将学习如何集成音乐播放器功能，处理不同音频格式，以及如何利用麦克风进行实时音频采集和处理。视频章节则关注于Android的视频播放、捕获和编码。开发者可以学习如何利用Android的摄像头API进行视频拍摄，以及如何播放本地和在线视频资源。同时，书籍可能还会涵盖视频剪辑、合成和流媒体服务的整合。最后，关于Web服务的部分，书中可能会讲述如何将多媒体内容与网络服务结合，实现内容的搜索、上传和分享。这包括使用API接口与其他服务（如社交媒体平台）进行交互，以便在应用程序中集成多媒体的社交功能。《Pro Android Media》是一本全面的指南，对于希望在Android平台上构建多媒体应用的开发者来说，它提供了丰富的实践示例和详尽的技术指导，无论你是初学者还是有经验的开发者，都能从中受益匪浅。通过这本书，你可以掌握创建下一代移动媒体应用所需的关键技能和策略。

CHAPTER 1: Introduction to Android Imaging

offer image capture capabilities on a par with the Camera application without having to

build their own custom capture routines.

An intent filter is a means for a programmer of an application to specify that their

application offers a specific capability. Specifying an intent filter in the

AndroidManifest.xml file of an application tells Android that this application and, in

particular, the activity that contains the intent filter will perform the specified task, on

command.

The Camera application has the following intent filter specified in its manifest file. The

intent filter shown here is contained within the “Camera” activity tags.

<intent-filter>

</intent-filter>

In order to utilize the Camera application via an intent, we simply have to construct an

intent that will be caught by the foregoing filter.

Intent i = new Intent("android.media.action.IMAGE_CAPTURE");

In practice, we probably don’t want to create the intent with that action string directly. In

this case, a constant is specified in the MediaStore class, ACTION_IMAGE_CAPTURE. The

reason we should use the constant rather than the string itself is that if the string

happens to change, it is likely that the constant will change as well, thereby making our

call a bit more future-proof than it would otherwise be.

Intent i = new Intent(android.provider.MediaStore.ACTION_IMAGE_CAPTURE);

startActivity(i);

Using this intent in a basic Android activity will cause the default Camera application to

launch in still picture mode, as shown in Figure 1–1.

Figure 1–1. The built-in Camera application as called from an intent shown running in an emulator

CHAPTER 1: Introduction to Android Imaging

<ImageView android:id="@+id/ReturnedImageView" android:layout_width="wrap_content"

android:layout_height="wrap_content"></ImageView>

</LinearLayout>

To complete the foregoing example, here are the contents of AndroidManifest.xml.

<?xml version="1.0" encoding="utf-8"?>

<manifest xmlns:android="http://schemas.android.com/apk/res/android"

android:versionCode="1"

android:versionName="1.0" package="com.apress.proandroidmedia.ch1.cameraintent">

<activity android:name=".CameraIntent"

android:label="@string/app_name">

<intent-filter>

</intent-filter>

</activity>

</application>

<uses-sdk android:minSdkVersion="4" />

</manifest>

In this example, the image is returned from the Camera application in an extra passed

through the intent that is sent to our calling activity in the onActivityResult method. The

name of the extra is "data" and it contains a Bitmap object, which needs to be cast from

a generic Object.

// Get Extras from the intent

Bundle extras = intent.getExtras();

// Get the returned image from that extra

Bitmap bmp = (Bitmap) extras.get("data");

In our layout XML (layout/main.xml) file, we have an ImageView. An ImageView is an

extension of a generic View, which supports the display of images. Since we have an

ImageView with the id ReturnedImageView specified, in our activity we need to obtain a

reference to that and set its Bitmap through its setImageBitmap method to be our

returned image. This enables the user of our application to view the image that was

captured.

To get a reference to the ImageView object, we use the standard findViewById method

specified in the Activity class. This method allows us to programmatically reference

elements specified in the layout XML file that we are using via setContentView by

passing in the id of the element. In the foregoing example, the ImageView object is

specified in the XML as follows:

<ImageView android:id="@+id/ReturnedImageView" android:layout_width="wrap_content"

android:layout_height="wrap_content"></ImageView>

To reference the ImageView and tell it to display the Bitmap from the Camera, we use

the following code.

imv = (ImageView) findViewById(R.id.ReturnedImageView);imv.setImageBitmap(bmp);

When you run this example, you’ll probably notice that the resulting image is small. (On

my phone, it is 121 pixels wide by 162 pixels tall. Other devices have different default

CHAPTER 1: Introduction to Android Imaging

NOTE: The foregoing code snippet for creating the URI to the image file could be simplified to the

following: imageFileUri =

Uri.parse("file:///sdcard/myfavoritepicture.jpg");

In practice, though, using the method shown will be more device-independent and future-proof

should the SD card–naming conventions or the URI syntax for the local filesystem change.

Displaying Large Images

Loading and displaying an image has significant memory usage implications. For

instance, the HTC G1 phone has a 3.2-megapixel camera. A 3.2-megapixel camera

typically captures images at 2048 pixels by 1536 pixels. Displaying a 32-bit image of

that size would take more than100663kb or approximately 13MB of memory. While this

may not guarantee that our application will run out of memory, it will certainly make it

more likely.

Android offers us a utility class called BitmapFactory, which provides a series of static

methods that allow the loading of Bitmap images from a variety of sources. For our

needs, we’ll be loading it from a file to display in our original activity. Fortunately, the

methods available in BitmapFactory take in a BitmapFactory.Options class, which

allows us to define how the Bitmap is read into memory. Specifically, we can set the

sample size that the BitmapFactory should use when loading an image. Indicating the

inSampleSize parameter in BitmapFactory.Options indicates that the resulting Bitmap

image will be that fraction of the size once loaded. For instance, setting the

inSampleSize to 8 as I do here would yield an image that is 1/8 the size of the original

image.

BitmapFactory.Options bmpFactoryOptions = new BitmapFactory.Options();

bmpFactoryOptions.inSampleSize = 8;

Bitmap bmp = BitmapFactory.decodeFile(imageFilePath, bmpFactoryOptions);

imv.setImageBitmap(bmp);

This is a quick way to load up a large image but doesn’t really take into account the

image’s original size nor the size of the screen. It would be better if we scaled the image

to something that would fit nicely on our screen.

The segments of code that follow illustrate how to use the dimensions of the display to

determine the amount of down sampling that should occur when loading the image.

When we use these methods, the image is assured of filling the bounds of the display as

much as possible. If, however, the image is only going to be shown at 100 pixels in any

one dimension, that value should be used instead of the display dimensions, which we

obtain as follows.

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