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[Android多媒体技术] 播放Raw/Assets音视频方法总结

前言

本文介绍如何通过系统MediaPlayerIjkPlayerExoPlayer分别播放安卓项目下的Raw或Assets文件夹中的音视频文件。

在某些情况下,我们会把一些音视频文件,如Mp3,Mp4等,直接放在安装包中的Raw或者Assets文件夹里,这些音视频文件可能作为特定场景的提示音,或者视频片头等等。关于Raw和Assets资源文件,这里不作过多讨论,总的来讲,他们都是被打包进APK中的文件,不会被编译成二进制,程序可以直接访问,无需额外的权限。

先说明一下本文代码的构建环境和使用的播放内核版本:

  • Java 1.7
  • Android Studio 3.1.2
  • Gradle 4.4
  • IjkPlayer 0.8.8
  • ExoPlayer 2.8.3

效果演示

Raw/Assets资源文件访问方式

在项目文件夹中的位置:

Raw文件访问方式

  • Raw文件位于res/raw目录下,Raw文件会被映射到R.java文件中,所以访问的时候直接使用资源ID即可,如
R.raw.raw_video
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或者获得该文件的AssetFileDescriptor:

AssetFileDescriptor afd = getResources().openRawResourceFd(R.raw.raw_video);
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Assets文件访问方式

  • Assets文件夹下的文件不会被映射到R.java中,访问的时候需要AssetManager类。
AssetManager am = getAssets();
try {
    AssetFileDescriptor afd= am.openFd(fileName);
} catch (IOException e) {
    e.printStackTrace();
}
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AssetFileDescriptor可以理解成访问Raw/Assets文件的一个入口,或者说是一把钥匙。

Raw/Assets文件还有其他的访问方式,比如通过ContentResolver,又或者直接开启一个InputStream去读取文件,这应该是播放器内核需要做的事情,我们只需要给播放器提供以上的信息即可。

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通过系统MediaPlayer播放音视频

  • Raw文件
//实例化播放内核
android.media.MediaPlayer mediaPlayer = new android.media.MediaPlayer();
//获得播放源访问入口
AssetFileDescriptor afd = getResources().openRawResourceFd(R.raw.raw_video); // 注意这里的区别
//给MediaPlayer设置播放源
mediaPlayer.setDataSource(afd.getFileDescriptor(), afd.getStartOffset(), afd.getLength());
//设置准备就绪状态监听
mediaPlayer.setOnPreparedListener(new MediaPlayer.OnPreparedListener() {
    @Override
    public void onPrepared(MediaPlayer mp) {
         // 开始播放
         mediaPlayer.start();
     }
});
//准备播放
mediaPlayer.prepareAsync();
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  • Assets 文件
//实例化播放内核
android.media.MediaPlayer mediaPlayer = new android.media.MediaPlayer();
//获得播放源访问入口
AssetManager am = getAssets();
try {
    AssetFileDescriptor afd = am.openFd("assets_video.mp4");// 注意这里的区别
    //给MediaPlayer设置播放源
    mediaPlayer.setDataSource(afd.getFileDescriptor(), afd.getStartOffset(), afd.getLength());
} catch (IOException e) {
    e.printStackTrace();
}
//设置准备就绪状态监听
mediaPlayer.setOnPreparedListener(new MediaPlayer.OnPreparedListener() {
    @Override
    public void onPrepared(MediaPlayer mp) {
         // 开始播放
         mediaPlayer.start();
     }
});
//准备播放
mediaPlayer.prepareAsync();
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代码中每一步都有注释,可以说非常详细了。简单总结一下,无论播放Raw文件还是Assets文件,我们首先获得AssetFileDescriptor,然后设置给MediaPlayer。

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通过IjkPlayer播放音视频

  • Raw 文件
//实例化播放内核
tv.danmaku.ijk.media.player.IjkMediaPlayer ijkPlayer = new tv.danmaku.ijk.media.player.IjkMediaPlayer();
//获得播放源访问入口
AssetFileDescriptor afd = getResources().openRawResourceFd(R.raw.raw_video); // 注意这里的区别
//构建IjkPlayer能识别的IMediaDataSource,下面的RawDataSourceProvider实现了IMediaDataSource接口
RawDataSourceProvider sourceProvider = new RawDataSourceProvider(fd);
//给IjkPlayer设置播放源
ijkPlayer.setDataSource(sourceProvider);
//设置准备就绪状态监听
ijkPlayer .setOnPreparedListener(new MediaPlayer.OnPreparedListener() {
    @Override
    public void onPrepared(MediaPlayer mp) {
         // 开始播放
         ijkPlayer.start();
     }
});
//准备播放
ijkPlayer.prepareAsync();
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  • Assets 文件
//实例化播放内核
tv.danmaku.ijk.media.player.IjkMediaPlayer ijkPlayer = new tv.danmaku.ijk.media.player.IjkMediaPlayer();
//获得播放源访问入口
AssetManager am = getAssets();
try {
    AssetFileDescriptor afd = am.openFd("assets_video.mp4");// 注意这里的区别
   //构建IjkPlayer能识别的IMediaDataSource,下面的RawDataSourceProvider实现了IMediaDataSource接口
    RawDataSourceProvider sourceProvider = new RawDataSourceProvider(fd);
    //给IjkPlayer设置播放源
    ijkPlayer.setDataSource(sourceProvider);
} catch (IOException e) {
    e.printStackTrace();
}
//设置准备就绪状态监听
ijkPlayer .setOnPreparedListener(new MediaPlayer.OnPreparedListener() {
    @Override
    public void onPrepared(MediaPlayer mp) {
         // 开始播放
         ijkPlayer.start();
     }
});
//准备播放
ijkPlayer.prepareAsync();
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补充下,其中的RawDataSourceProvider实现了IMediaDataSource 接口,IMediaDataSourceIjkPlayer包中的接口,实现了IMediaDataSource接口的类可以设置给IjkPlayer作为播放源。就像下面这样:

import tv.danmaku.ijk.media.player.misc.IMediaDataSource;

public class RawDataSourceProvider implements IMediaDataSource {
    private AssetFileDescriptor mDescriptor;
    private byte[] mMediaBytes;
    public RawDataSourceProvider(AssetFileDescriptor descriptor) {
        this.mDescriptor = descriptor;
    }

    @Override
    public int readAt(long position, byte[] buffer, int offset, int size) {
        if (position + 1 >= mMediaBytes.length) {
            return -1;
        }
        int length;
        if (position + size < mMediaBytes.length) {
            length = size;
        } else {
            length = (int) (mMediaBytes.length - position);
            if (length > buffer.length)
                length = buffer.length;
            length--;
        }
        // 把文件内容copy到buffer中;
        System.arraycopy(mMediaBytes, (int) position, buffer, offset, length);
        return length;
    }

    @Override
    public long getSize() throws IOException {
        long length = mDescriptor.getLength();
        if (mMediaBytes == null) {
            InputStream inputStream = mDescriptor.createInputStream();
            mMediaBytes = readBytes(inputStream);
        }
        return length;
    }

    @Override
    public void close() throws IOException {
        if (mDescriptor != null)
            mDescriptor.close();
        mDescriptor = null;
        mMediaBytes = null;
    }

    //读取文件内容
    private byte[] readBytes(InputStream inputStream) throws IOException {
        ByteArrayOutputStream byteBuffer = new ByteArrayOutputStream();
        int bufferSize = 1024;
        byte[] buffer = new byte[bufferSize];
        int len;
        while ((len = inputStream.read(buffer)) != -1) {
            byteBuffer.write(buffer, 0, len);
        }
        return byteBuffer.toByteArray();
    }
}

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小结一下,我们首先获取到Raw/Assets文件的AssetFileDescriptor,然后用它去构建一个IMediaDataSource,最后设置给IjkPlayer

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通过ExoPlayer播放音视频

  • ExoPlayer播放器内核的实例化有点复杂,这里单独写
//实例化播放内核
TrackSelection.Factory videoTrackSelectionFactory =
                    new AdaptiveTrackSelection.Factory(new DefaultBandwidthMeter());
DefaultTrackSelector mTrackSelector = new DefaultTrackSelector(videoTrackSelectionFactory);
boolean preferExtensionDecoders = true;
boolean useExtensionRenderers = true;//是否开启扩展
@DefaultRenderersFactory.ExtensionRendererMode int extensionRendererMode = useExtensionRenderers
                    ? (preferExtensionDecoders ? DefaultRenderersFactory.EXTENSION_RENDERER_MODE_PREFER
                    : DefaultRenderersFactory.EXTENSION_RENDERER_MODE_ON)
                    : DefaultRenderersFactory.EXTENSION_RENDERER_MODE_OFF;

DefaultRenderersFactory rendererFactory = new DefaultRenderersFactory(mAppContext, extensionRendererMode);
DefaultLoadControl loadControl = new DefaultLoadControl();
//工厂方法获得播放器实例
om.google.android.exoplayer2.SimpleExoPlayer exoPlayer = 
             ExoPlayerFactory.newSimpleInstance(rendererFactory, mTrackSelector, loadControl, null);
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  • Raw 文件
//构建Raw文件播放源--RawResourceDataSource
DataSpec dataSpec = new DataSpec(RawResourceDataSource.buildRawResourceUri(R.raw.raw_video));
RawResourceDataSource rawResourceDataSource = new RawResourceDataSource(this);
try {
    rawResourceDataSource.open(dataSpec);
} catch (RawResourceDataSource.RawResourceDataSourceException e) {
    e.printStackTrace();
}
//构建ExoPlayer能识别的播放源--MediaSource 
String url = rawDataSource.getUri().toString();
MediaSource mediaSource = ExoSourceManager.newInstance(mAppContext, getHeaders()).getMediaSource(
                    url, false, false, MediaPlayerManager.instance().isLooping(), null
            );
//给ExoPlayer设置播放源,并准备播放
exoPlayer.prepare(mediaSource);
//让ExoPlayer准备好后就开始播放
exoPlayer.setPlayWhenReady(true);
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  • Assets 文件
//构建ExoPlayer能识别的播放源--MediaSource 
String url = "file:///android_asset/" + "assets_video.mp4";
MediaSource mediaSource = ExoSourceManager.newInstance(mAppContext, getHeaders()).getMediaSource(
                    url, false, false, MediaPlayerManager.instance().isLooping(), null
            );
//给ExoPlayer设置播放源,并准备播放
exoPlayer.prepare(mediaSource);
//让ExoPlayer准备好后就开始播放
exoPlayer.setPlayWhenReady(true);
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小结:ExoPlayer实例化的时候复杂一点,需要按照官方文档一步步来。播放Raw文件的时候,需要先构建出RawResourceDataSource,这是ExoPlayer为了播放Raw音视频文件提供的类,然后获取其中的Uri构建MediaSource,最后设置给ExoPlayer。播放Assets文件就更简单了,形如String url = "file:///android_asset/" + "filename"的Assets文件播放地址可以直接用来构建MediaSource

项目地址:github.com/maiwenchang… 欢迎各位Star~~