请尊重分享成果，转载请注明出处,本文来自逆流的鱼yuiop,原文链接：http://blog.csdn.net/hejjunlin/article/details/53729575
前言：前面几章都是分析MediaCodec相关源码，有收到提问，说MediaCodec到底是硬解码还是软解码？看下今天的Agenda:
- MediaCodec到底是硬解码还是软解码
- MediaMuxer初识
- MediaMuxer与MediaExtractor进行剪辑视频
- 效果图
- 布局实现
- 逻辑实现
- log输出过程
MediaCodec到底是硬解码还是软解码？
MediaCodec 调用的是在系统中register的解码器，硬件厂商会把自己的硬解码器register进来，就是硬解，如果他register一个软解码器，则是软解。
MediaCodec并不是真正的codec，真正codec是在openMax，要保证是硬解，在MediaCodec里有接口可以枚举所有解码器，每种编码可能都有多个解码器，区分哪个是软解哪个是硬解就行。
MediaCodec mediaCodec = MediaCodec.createDecoderByType("video/avc");我的应用里面接收的是H264编码数据，所以我选取的是video/avc，我们可以看一下MediaCodec.createDecoderByType（）枚举了哪些解编码器：
> /**
> * Instantiate a decoder supporting input data of the given mime type.
> *
> * The following is a partial list of defined mime types and their semantics:
> * <ul>
> * <li>"video/x-vnd.on2.vp8" - VP8 video (i.e. video in .webm)
> * <li>"video/x-vnd.on2.vp9" - VP9 video (i.e. video in .webm)
> * <li>"video/avc" - H.264/AVC video
> * <li>"video/mp4v-es" - MPEG4 video
> * <li>"video/3gpp" - H.263 video
> * <li>"audio/3gpp" - AMR narrowband audio
> * <li>"audio/amr-wb" - AMR wideband audio
> * <li>"audio/mpeg" - MPEG1/2 audio layer III
> * <li>"audio/mp4a-latm" - AAC audio (note, this is raw AAC packets, not packaged in LATM!)
> * <li>"audio/vorbis" - vorbis audio
> * <li>"audio/g711-alaw" - G.711 alaw audio
> * <li>"audio/g711-mlaw" - G.711 ulaw audio
> * </ul>
> *
> * @param type The mime type of the input data.
> */
> public static MediaCodec createDecoderByType(String type) {
> return new MediaCodec(type, true /* nameIsType */, false /* encoder */);
> }可以看到我选的”video/avc” - H.264/AVC video是一种H264的解码方式，但并不能证明我使用的就一定是硬解码
我们先来看一下Android系统中解码器的命名，软解码器通常是以OMX.google开头的。硬解码器通常是以OMX.[hardware_vendor]开头的，比如TI的解码器是以OMX.TI开头的。当然还有一些不遵守这个命名规范的，不以OMX.开头的，那也会被认为是软解码器。
判断规则见frameworks/av/media/libstagefright/OMXCodec.cpp：
static bool IsSoftwareCodec(const char *componentName) {
if (!strncmp("OMX.google.", componentName, 11)) {
return true;
}
if (!strncmp("OMX.", componentName, 4)) {
return false;
}
return true;
}其实MediaCodec调用的是在系统中注册的解码器，系统中存在的解码器可以很多，但能够被应用使用的解码器是根据配置来的，即/system/etc/media_codecc.xml。这个文件一般由硬件或者系统的生产厂家在build整个系统的时候提供，一般是保存在代码的device/[company]/[codename]目录下的，例如device/samsung/tuna/media_codecs.xml。这个文件配置了系统中有哪些可用的codec以及，这些codec对应的媒体文件类型。在这个文件里面，系统里面提供的软硬codec都需要被列出来。
也就是说，如果系统里面实际上包含了某个codec，但是并没有被配置在这个文件里，那么应用程序也无法使用到。
在这个配置文件里面，如果出现多个codec对应同样类型的媒体格式的时候，这些codec都会被保留起来。当系统使用的时候，将会选择第一个匹配的codec。除非是指明了要软解码还是硬解码，但是Android的framework层为上层提供服务的AwesomePlayer中在处理音频和视频的时候，对到底是选择软解还是硬解的参数没有设置。所以虽然底层是支持选择的，但是对于上层使用MediaPlayer的Java程序来说，还是只能接受默认的codec选取规则。
但是Android提供的命令行程序/system/bin/stagefright在播放音频文件的时候，倒是可以根据参数来选择到底使用软解码还是硬解码，但是该工具只支持播放音频，不支持播放视频。
一般来说，如果系统里面有对应的媒体硬件解码器的话，系统开发人员应该是会配置在media_codecs.xml中，所以大多数情况下，如果有硬件解码器，那么我们总是会使用到硬件解码器。极少数情况下，硬件解码器存在，但不配置，我猜只可能是这个硬解码器还有bug，暂时还不适合发布，所以不用使用。
MediaMuxer初识
今天主要介绍MediaMuxer，在Android的多媒体类中，MediaMuxer用于将音频和视频进行混合生成多媒体文件。缺点是目前只能支持一个audio track和一个video track，而且仅支持mp4输出。
通过一个案列来了解MediaMuxer，以便后续过程分析，这个案例是进行一个音视频剪辑。就是一段正常的音视频文件，剪辑其中一个片段。在我的手机上有一段叫《节目.mp4》音视频文件。想剪辑其中精华部分，从2秒到12秒的视频。如下为效果图
效果图：
输入剪辑时间点，可以动态设置，并不是写死，剪辑时长，也是可以动态设置。
节目_output.mp4就是剪辑后的音视频文件。 
布局实现：
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:padding="10dp"
android:orientation="horizontal">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textSize="18sp"
android:text="开始剪辑点(从第几秒开始):"/>
<EditText
android:id="@+id/et_cutpoint"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="@null"
android:textSize="18sp"
android:layout_marginLeft="5dp"
android:hint="2"/>
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:padding="10dp"
android:orientation="horizontal">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textSize="18sp"
android:text="剪辑时长(剪辑多少秒):"/>
<EditText
android:id="@+id/et_cutduration"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="@null"
android:textSize="18sp"
android:layout_marginLeft="5dp"
android:hint="10"/>
</LinearLayout>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/button"
android:padding="10dp"
android:background="@drawable/selector_green_bg"
android:layout_gravity="center"
android:textColor="@color/white"
android:text="剪切视频" />
</LinearLayout>本文来自逆流的鱼yuiop,原文链接：http://blog.csdn.net/hejjunlin/article/details/53729575
逻辑实现：
package com.hejunlin.videoclip;
import android.media.MediaCodec;
import android.media.MediaExtractor;
import android.media.MediaFormat;
import android.media.MediaMuxer;
import android.util.Log;
import java.nio.ByteBuffer;
/**
* Created by 逆流的鱼yuiop on 16/12/18.
* blog : http://blog.csdn.net/hejjunlin
*/
public class VideoClip {
private final static String TAG = "VideoClip";
private MediaExtractor mMediaExtractor;
private MediaFormat mMediaFormat;
private MediaMuxer mMediaMuxer;
private String mime = null;
public boolean clipVideo(String url, long clipPoint, long clipDuration) {
int videoTrackIndex = -1;
int audioTrackIndex = -1;
int videoMaxInputSize = 0;
int audioMaxInputSize = 0;
int sourceVTrack = 0;
int sourceATrack = 0;
long videoDuration, audioDuration;
Log.d(TAG, ">> url : " + url);
//创建分离器
mMediaExtractor = new MediaExtractor();
try {
//设置文件路径
mMediaExtractor.setDataSource(url);
//创建合成器
mMediaMuxer = new MediaMuxer(url.substring(0, url.lastIndexOf(".")) + "_output.mp4", MediaMuxer.OutputFormat.MUXER_OUTPUT_MPEG_4);
} catch (Exception e) {
Log.e(TAG, "error path" + e.getMessage());
}
//获取每个轨道的信息
for (int i = 0; i < mMediaExtractor.getTrackCount(); i++) {
try {
mMediaFormat = mMediaExtractor.getTrackFormat(i);
mime = mMediaFormat.getString(MediaFormat.KEY_MIME);
if (mime.startsWith("video/")) {
sourceVTrack = i;
int width = mMediaFormat.getInteger(MediaFormat.KEY_WIDTH);
int height = mMediaFormat.getInteger(MediaFormat.KEY_HEIGHT);
videoMaxInputSize = mMediaFormat.getInteger(MediaFormat.KEY_MAX_INPUT_SIZE);
videoDuration = mMediaFormat.getLong(MediaFormat.KEY_DURATION);
//检测剪辑点和剪辑时长是否正确
if (clipPoint >= videoDuration) {
Log.e(TAG, "clip point is error!");
return false;
}
if ((clipDuration != 0) && ((clipDuration + clipPoint) >= videoDuration)) {
Log.e(TAG, "clip duration is error!");
return false;
}
Log.d(TAG, "width and height is " + width + " " + height
+ ";maxInputSize is " + videoMaxInputSize
+ ";duration is " + videoDuration
);
//向合成器添加视频轨
videoTrackIndex = mMediaMuxer.addTrack(mMediaFormat);
} else if (mime.startsWith("audio/")) {
sourceATrack = i;
int sampleRate = mMediaFormat.getInteger(MediaFormat.KEY_SAMPLE_RATE);
int channelCount = mMediaFormat.getInteger(MediaFormat.KEY_CHANNEL_COUNT);
audioMaxInputSize = mMediaFormat.getInteger(MediaFormat.KEY_MAX_INPUT_SIZE);
audioDuration = mMediaFormat.getLong(MediaFormat.KEY_DURATION);
Log.d(TAG, "sampleRate is " + sampleRate
+ ";channelCount is " + channelCount
+ ";audioMaxInputSize is " + audioMaxInputSize
+ ";audioDuration is " + audioDuration
);
//添加音轨
audioTrackIndex = mMediaMuxer.addTrack(mMediaFormat);
}
Log.d(TAG, "file mime is " + mime);
} catch (Exception e) {
Log.e(TAG, " read error " + e.getMessage());
}
}
//分配缓冲
ByteBuffer inputBuffer = ByteBuffer.allocate(videoMaxInputSize);
//根据官方文档的解释MediaMuxer的start一定要在addTrack之后
mMediaMuxer.start();
//视频处理部分
mMediaExtractor.selectTrack(sourceVTrack);
MediaCodec.BufferInfo videoInfo = new MediaCodec.BufferInfo();
videoInfo.presentationTimeUs = 0;
long videoSampleTime;
//获取源视频相邻帧之间的时间间隔。(1)
{
mMediaExtractor.readSampleData(inputBuffer, 0);
//skip first I frame
if (mMediaExtractor.getSampleFlags() == MediaExtractor.SAMPLE_FLAG_SYNC)
mMediaExtractor.advance();
mMediaExtractor.readSampleData(inputBuffer, 0);
long firstVideoPTS = mMediaExtractor.getSampleTime();
mMediaExtractor.advance();
mMediaExtractor.readSampleData(inputBuffer, 0);
long SecondVideoPTS = mMediaExtractor.getSampleTime();
videoSampleTime = Math.abs(SecondVideoPTS - firstVideoPTS);
Log.d(TAG, "videoSampleTime is " + videoSampleTime);
}
//选择起点
mMediaExtractor.seekTo(clipPoint, MediaExtractor.SEEK_TO_PREVIOUS_SYNC);
while (true) {
int sampleSize = mMediaExtractor.readSampleData(inputBuffer, 0);
if (sampleSize < 0) {
//这里一定要释放选择的轨道，不然另一个轨道就无法选中了
mMediaExtractor.unselectTrack(sourceVTrack);
break;
}
int trackIndex = mMediaExtractor.getSampleTrackIndex();
//获取时间戳
long presentationTimeUs = mMediaExtractor.getSampleTime();
//获取帧类型，只能识别是否为I帧
int sampleFlag = mMediaExtractor.getSampleFlags();
Log.d(TAG, "trackIndex is " + trackIndex
+ ";presentationTimeUs is " + presentationTimeUs
+ ";sampleFlag is " + sampleFlag
+ ";sampleSize is " + sampleSize);
//剪辑时间到了就跳出
if ((clipDuration != 0) && (presentationTimeUs > (clipPoint + clipDuration))) {
mMediaExtractor.unselectTrack(sourceVTrack);
break;
}
mMediaExtractor.advance();
videoInfo.offset = 0;
videoInfo.size = sampleSize;
videoInfo.flags = sampleFlag;
mMediaMuxer.writeSampleData(videoTrackIndex, inputBuffer, videoInfo);
videoInfo.presentationTimeUs += videoSampleTime;//presentationTimeUs;
}
//音频部分
mMediaExtractor.selectTrack(sourceATrack);
MediaCodec.BufferInfo audioInfo = new MediaCodec.BufferInfo();
audioInfo.presentationTimeUs = 0;
long audioSampleTime;
//获取音频帧时长
{
mMediaExtractor.readSampleData(inputBuffer, 0);
//skip first sample
if (mMediaExtractor.getSampleTime() == 0)
mMediaExtractor.advance();
mMediaExtractor.readSampleData(inputBuffer, 0);
long firstAudioPTS = mMediaExtractor.getSampleTime();
mMediaExtractor.advance();
mMediaExtractor.readSampleData(inputBuffer, 0);
long SecondAudioPTS = mMediaExtractor.getSampleTime();
audioSampleTime = Math.abs(SecondAudioPTS - firstAudioPTS);
Log.d(TAG, "AudioSampleTime is " + audioSampleTime);
}
mMediaExtractor.seekTo(clipPoint, MediaExtractor.SEEK_TO_CLOSEST_SYNC);
while (true) {
int sampleSize = mMediaExtractor.readSampleData(inputBuffer, 0);
if (sampleSize < 0) {
mMediaExtractor.unselectTrack(sourceATrack);
break;
}
int trackIndex = mMediaExtractor.getSampleTrackIndex();
long presentationTimeUs = mMediaExtractor.getSampleTime();
Log.d(TAG, "trackIndex is " + trackIndex
+ ";presentationTimeUs is " + presentationTimeUs);
if ((clipDuration != 0) && (presentationTimeUs > (clipPoint + clipDuration))) {
mMediaExtractor.unselectTrack(sourceATrack);
break;
}
mMediaExtractor.advance();
audioInfo.offset = 0;
audioInfo.size = sampleSize;
mMediaMuxer.writeSampleData(audioTrackIndex, inputBuffer, audioInfo);
audioInfo.presentationTimeUs += audioSampleTime;//presentationTimeUs;
}
//全部写完后释放MediaMuxer和MediaExtractor
mMediaMuxer.stop();
mMediaMuxer.release();
mMediaExtractor.release();
mMediaExtractor = null;
return true;
}
}ClipActivity
package com.hejunlin.videoclip;
import android.annotation.TargetApi;
import android.os.Build;
import android.os.Bundle;
import android.os.Environment;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
/**
* Created by 逆流的鱼yuiop on 16/12/18.
* blog : http://blog.csdn.net/hejjunlin
*/
public class ClipActivity extends AppCompatActivity implements View.OnClickListener {
private Button mButton;
private EditText mCutDuration;
private EditText mCutPoint;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main1);
mButton = (Button) findViewById(R.id.button);
mCutDuration = (EditText) findViewById(R.id.et_cutduration);
mCutPoint = (EditText)findViewById(R.id.et_cutpoint);
mButton.setOnClickListener(this);
}
@TargetApi(Build.VERSION_CODES.LOLLIPOP)
@Override
public void onClick(View v) {
new VideoClip().clipVideo(
Environment.getExternalStorageDirectory() + "/" + "节目.mp4",
Integer.parseInt(mCutPoint.getText().toString())*1000*1000,
Integer.parseInt(mCutDuration.getText().toString())*1000*1000);
}
}log输出过程
12-18 19:04:49.212 22409-22409/com.hejunlin.videoclip
D/VideoClip: >> url : /storage/emulated/0/节目.mp4
12-18 19:04:49.364 22409-22409/com.hejunlin.videoclip
D/VideoClip: width and height is 480 272;maxInputSize is 25326;duration is 125266666
12-18 19:04:49.365 22409-22409/com.hejunlin.videoclip
D/VideoClip: file mime is video/avc
12-18 19:04:49.366 22409-22409/com.hejunlin.videoclip
D/VideoClip: sampleRate is 24000;channelCount is 2;audioMaxInputSize is 348;audioDuration is 125440000
12-18 19:04:49.366 22409-22409/com.hejunlin.videoclip
D/VideoClip: file mime is audio/mp4a-latm
12-18 19:04:49.370 22409-22409/com.hejunlin.videoclip
D/VideoClip: videoSampleTime is 66667
12-18 19:04:49.372 22409-22409/com.hejunlin.videoclip
D/VideoClip: trackIndex is 0;presentationTimeUs is 0;sampleFlag is 1;sampleSize is 19099
12-18 19:04:49.373 22409-22409/com.hejunlin.videoclip
D/VideoClip: trackIndex is 0;presentationTimeUs is 66666;sampleFlag is 0;sampleSize is 451
12-18 19:04:49.374 22409-22409/com.hejunlin.videoclip
D/VideoClip: trackIndex is 0;presentationTimeUs is 133333;sampleFlag is 0;sampleSize is 521
12-18 19:04:49.374 22409-22409/com.hejunlin.videoclip
D/VideoClip: trackIndex is 0;presentationTimeUs is 200000;sampleFlag is 0;sampleSize is 738
12-18 19:04:49.375 22409-22409/com.hejunlin.videoclip
D/VideoClip: trackIndex is 0;presentationTimeUs is 266666;sampleFlag is 0;sampleSize is 628
12-18 19:04:49.376 22409-22409/com.hejunlin.videoclip
D/VideoClip: trackIndex is 0;presentationTimeUs is 333333;sampleFlag is 0;sampleSize is 267
12-18 19:04:49.376 22409-22409/com.hejunlin.videoclip
D/VideoClip: trackIndex is 0;presentationTimeUs is 400000;sampleFlag is 0;sampleSize is 4003
12-18 19:04:49.377 22409-22409/com.hejunlin.videoclip
D/VideoClip: trackIndex is 0;presentationTimeUs is 466666;sampleFlag is 0;sampleSize is 2575
12-18 19:04:49.377 22409-22409/com.hejunlin.videoclip
D/VideoClip: trackIndex is 0;presentationTimeUs is 533333;sampleFlag is 0;sampleSize is 1364
12-18 19:04:49.378 22409-22409/com.hejunlin.videoclip
D/VideoClip: trackIndex is 0;presentationTimeUs is 600000;sampleFlag is 0;sampleSize is 3019
12-18 19:04:49.379 22409-22409/com.hejunlin.videoclip
D/VideoClip: trackIndex is 0;presentationTimeUs is 666666;sampleFlag is 0;sampleSize is 4595
12-18 19:04:49.379 22409-22409/com.hejunlin.videoclip
D/VideoClip: trackIndex is 0;presentationTimeUs is 733333;sampleFlag is 0;sampleSize is 3689
... 省略log
12-18 19:04:49.467 22409-22409/com.hejunlin.videoclip
D/VideoClip: AudioSampleTime is 42667
12-18 19:04:49.468 22409-22409/com.hejunlin.videoclip
D/VideoClip: trackIndex is 1;presentationTimeUs is 2005333
12-18 19:04:49.469 22409-22409/com.hejunlin.videoclip
D/VideoClip: trackIndex is 1;presentationTimeUs is 2048000
12-18 19:04:49.469 22409-22409/com.hejunlin.videoclip
D/VideoClip: trackIndex is 1;presentationTimeUs is 2090666
12-18 19:04:49.470 22409-22409/com.hejunlin.videoclip
D/VideoClip: trackIndex is 1;presentationTimeUs is 2133333
12-18 19:04:49.470 22409-22409/com.hejunlin.videoclip
... 省略log
D/VideoClip: trackIndex is 1;presentationTimeUs is 12032000第一时间获得博客更新提醒，以及更多android干货，源码分析，欢迎关注我的微信公众号，扫一扫下方二维码或者长按识别二维码，即可关注。
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