精通Android媒体开发：打造图形、音乐、视频和富媒体应用

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"Pro Android Media: Developing Graphics, Music, Video and Rich Media Apps for Smartphones and Tablets" 是一本由 Shawn VanEvery 撰写的关于安卓开发的专业书籍，主要关注于使用Android媒体API来创建动态的移动应用。这本书深入探讨了在安卓平台上开发图形、音乐、视频以及丰富的多媒体应用的关键技术。它涵盖了以下核心知识点： 1. **Android Media APIs**：书中详细介绍了如何利用Android提供的媒体API来处理音频、视频和图像。这些API包括MediaPlayer、Camera、SurfaceView、AudioTrack、Visualizer等，用于播放、录制、编辑和显示多媒体内容。 2. **图形与动画**：开发者将学习如何使用OpenGL ES进行2D和3D图形渲染，以及如何创建流畅的动画效果，这包括使用Canvas、Bitmap、Path以及动画框架如Property Animation。 3. **音乐与音频处理**：书中有专门章节讲述如何集成音乐播放功能，使用MediaPlayer或ExoPlayer库，以及如何处理音频流、混音和音频特效。 4. **视频处理**：介绍如何捕获、编码和解码视频，以及如何在应用中实现视频播放器。可能涉及的API有MediaRecorder、MediaCodec以及MediaExtractor。 5. **富媒体应用开发**：讨论如何构建混合媒体应用，例如结合图像、音频和视频元素，创建交互式体验，可能涵盖到多媒体数据库管理、流媒体服务集成等。 6. **硬件加速与性能优化**：探讨如何利用硬件加速提升应用性能，减少内存占用，并提供性能调优的策略和技巧。 7. **兼容性和版本管理**：由于Android的碎片化问题，书里会指导开发者如何确保应用在不同设备和Android版本上的兼容性。 8. **第三方库与工具**：介绍一些流行的开源库，如Volley、Picasso、Retrofit等，以及如何利用它们来简化多媒体开发。 9. **实践项目**：书中可能包含实际的开发项目案例，通过实际操作帮助读者理解理论知识并提升实践能力。 10. **调试与测试**：讲解如何有效地调试多媒体应用，包括日志分析、性能监控以及如何设计有效的测试策略。这本书对于希望深入理解和掌握Android平台多媒体开发的开发者来说是一本宝贵的资源。尽管原文是英文，但通过网络搜索可以找到中文版，以方便非英语母语的开发者阅读。

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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精通Android媒体开发：打造图形、音乐、视频和富媒体应用

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