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前言：前面幾章都是分析MediaCodec相關源碼，有收到提問，說MediaCodec到底是硬解碼還是軟解碼？看下今天的Agenda:
MediaCodec到底是硬解碼還是軟解碼 MediaMuxer初識 MediaMuxer與MediaExtractor進行剪輯視頻 效果圖 布局實現 邏輯實現 log輸出過程MediaCodec到底是硬解碼還是軟解碼？
MediaCodec 調用的是在系統中register的解碼器，硬件廠商會把自己的硬解碼器register進來，就是硬解，如果他register一個軟解碼器，則是軟解。
MediaCodec并不是真正的codec，真正codec是在openMax，要保證是硬解，在MediaCodec里有接口可以枚舉所有解碼器，每種編碼可能都有多個解碼器，區分哪個是軟解哪個是硬解就行。
MediaCodec mediaCodec = MediaCodec.createDecoderByType("video/avc");我的應用里面接收的是H264編碼數據，所以我選取的是video/avc，我們可以看一下MediaCodec.createDecoderByType（）枚舉了哪些解編碼器：
> /**> * Instantiate a decoder supporting input data of the given mime type.> *> * The following is a partial list of defined mime types and their semantics:> * > *"video/x-vnd.on2.vp8" - VP8 video (i.e. video in .webm) > *"video/x-vnd.on2.vp9" - VP9 video (i.e. video in .webm) > *"video/avc" - H.264/AVC video > *"video/mp4v-es" - MPEG4 video > *"video/3gpp" - H.263 video > *"audio/3gpp" - AMR narrowband audio > *"audio/amr-wb" - AMR wideband audio > *"audio/mpeg" - MPEG1/2 audio layer III > *"audio/mp4a-latm" - AAC audio (note, this is raw AAC packets, not packaged in LATM!) > *"audio/vorbis" - vorbis audio > *"audio/g711-alaw" - G.711 alaw audio > *"audio/g711-mlaw" - G.711 ulaw audio > *> * > * @param type The mime type of the input data. > */ > public static MediaCodec createDecoderByType(String type) { > return new MediaCodec(type, true /* nameIsType */, false /* encoder */); > }可以看到我選的”video/avc” - H.264/AVC video是一種H264的解碼方式，但并不能證明我使用的就一定是硬解碼
我們先來看一下Android系統中解碼器的命名，軟解碼器通常是以OMX.google開頭的。硬解碼器通常是以OMX.[hardware_vendor]開頭的，比如TI的解碼器是以OMX.TI開頭的。當然還有一些不遵守這個命名規范的，不以OMX.開頭的，那也會被認為是軟解碼器。
判斷規則見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;}其實MediaCodec調用的是在系統中注冊的解碼器，系統中存在的解碼器可以很多，但能夠被應用使用的解碼器是根據配置來的，即/system/etc/media_codecc.xml。這個文件一般由硬件或者系統的生產廠家在build整個系統的時候提供，一般是保存在代碼的device/[company]/[codename]目錄下的，例如device/samsung/tuna/media_codecs.xml。這個文件配置了系統中有哪些可用的codec以及，這些codec對應的媒體文件類型。在這個文件里面，系統里面提供的軟硬codec都需要被列出來。
也就是說，如果系統里面實際上包含了某個codec，但是并沒有被配置在這個文件里，那么應用程序也無法使用到。
在這個配置文件里面，如果出現多個codec對應同樣類型的媒體格式的時候，這些codec都會被保留起來。當系統使用的時候，將會選擇第一個匹配的codec。除非是指明了要軟解碼還是硬解碼，但是Android的framework層為上層提供服務的AwesomePlayer中在處理音頻和視頻的時候，對到底是選擇軟解還是硬解的參數沒有設置。所以雖然底層是支持選擇的，但是對于上層使用MediaPlayer的Java程序來說，還是只能接受默認的codec選取規則。
但是Android提供的命令行程序/system/bin/stagefright在播放音頻文件的時候，倒是可以根據參數來選擇到底使用軟解碼還是硬解碼，但是該工具只支持播放音頻，不支持播放視頻。
一般來說，如果系統里面有對應的媒體硬件解碼器的話，系統開發人員應該是會配置在media_codecs.xml中，所以大多數情況下，如果有硬件解碼器，那么我們總是會使用到硬件解碼器。極少數情況下，硬件解碼器存在，但不配置，我猜只可能是這個硬解碼器還有bug，暫時還不適合發布，所以不用使用。
MediaMuxer初識
今天主要介紹MediaMuxer，在Android的多媒體類中，MediaMuxer用于將音頻和視頻進行混合生成多媒體文件。缺點是目前只能支持一個audio track和一個video track，而且僅支持mp4輸出。
通過一個案列來了解MediaMuxer，以便后續過程分析，這個案例是進行一個音視頻剪輯。就是一段正常的音視頻文件，剪輯其中一個片段。在我的手機上有一段叫《節目.mp4》音視頻文件。想剪輯其中精華部分，從2秒到12秒的視頻。如下為效果圖
效果圖：
輸入剪輯時間點，可以動態設置，并不是寫死，剪輯時長，也是可以動態設置。
節目_output.mp4就是剪輯后的音視頻文件。
布局實現：
邏輯實現：
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 逆流的魚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); //創建分離器 mMediaExtractor = new MediaExtractor(); try { //設置文件路徑 mMediaExtractor.setDataSource(url); //創建合成器 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()); } //獲取每個軌道的信息 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); //檢測剪輯點和剪輯時長是否正確 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 ); //向合成器添加視頻軌 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 ); //添加音軌 audioTrackIndex = mMediaMuxer.addTrack(mMediaFormat); } Log.d(TAG, "file mime is " + mime); } catch (Exception e) { Log.e(TAG, " read error " + e.getMessage()); } } //分配緩沖 ByteBuffer inputBuffer = ByteBuffer.allocate(videoMaxInputSize); //根據官方文檔的解釋MediaMuxer的start一定要在addTrack之后 mMediaMuxer.start(); //視頻處理部分 mMediaExtractor.selectTrack(sourceVTrack); MediaCodec.BufferInfo videoInfo = new MediaCodec.BufferInfo(); videoInfo.presentationTimeUs = 0; long videoSampleTime; //獲取源視頻相鄰幀之間的時間間隔。(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); } //選擇起點 mMediaExtractor.seekTo(clipPoint, MediaExtractor.SEEK_TO_PREVIOUS_SYNC); while (true) { int sampleSize = mMediaExtractor.readSampleData(inputBuffer, 0); if (sampleSize < 0) { //這里一定要釋放選擇的軌道，不然另一個軌道就無法選中了 mMediaExtractor.unselectTrack(sourceVTrack); break; } int trackIndex = mMediaExtractor.getSampleTrackIndex(); //獲取時間戳 long presentationTimeUs = mMediaExtractor.getSampleTime(); //獲取幀類型，只能識別是否為I幀 int sampleFlag = mMediaExtractor.getSampleFlags(); Log.d(TAG, "trackIndex is " + trackIndex + ";presentationTimeUs is " + presentationTimeUs + ";sampleFlag is " + sampleFlag + ";sampleSize is " + sampleSize); //剪輯時間到了就跳出 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; } //音頻部分 mMediaExtractor.selectTrack(sourceATrack); MediaCodec.BufferInfo audioInfo = new MediaCodec.BufferInfo(); audioInfo.presentationTimeUs = 0; long audioSampleTime; //獲取音頻幀時長 { 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; } //全部寫完后釋放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 逆流的魚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() + "/" + "節目.mp4", Integer.parseInt(mCutPoint.getText().toString())*1000*1000, Integer.parseInt(mCutDuration.getText().toString())*1000*1000); }}log輸出過程
12-18 19:04:49.212 22409-22409/com.hejunlin.videoclipD/VideoClip: >> url : /storage/emulated/0/節目.mp412-18 19:04:49.364 22409-22409/com.hejunlin.videoclipD/VideoClip: width and height is 480 272;maxInputSize is 25326;duration is 12526666612-18 19:04:49.365 22409-22409/com.hejunlin.videoclipD/VideoClip: file mime is video/avc12-18 19:04:49.366 22409-22409/com.hejunlin.videoclipD/VideoClip: sampleRate is 24000;channelCount is 2;audioMaxInputSize is 348;audioDuration is 12544000012-18 19:04:49.366 22409-22409/com.hejunlin.videoclipD/VideoClip: file mime is audio/mp4a-latm12-18 19:04:49.370 22409-22409/com.hejunlin.videoclipD/VideoClip: videoSampleTime is 6666712-18 19:04:49.372 22409-22409/com.hejunlin.videoclipD/VideoClip: trackIndex is 0;presentationTimeUs is 0;sampleFlag is 1;sampleSize is 1909912-18 19:04:49.373 22409-22409/com.hejunlin.videoclipD/VideoClip: trackIndex is 0;presentationTimeUs is 66666;sampleFlag is 0;sampleSize is 45112-18 19:04:49.374 22409-22409/com.hejunlin.videoclipD/VideoClip: trackIndex is 0;presentationTimeUs is 133333;sampleFlag is 0;sampleSize is 52112-18 19:04:49.374 22409-22409/com.hejunlin.videoclipD/VideoClip: trackIndex is 0;presentationTimeUs is 200000;sampleFlag is 0;sampleSize is 73812-18 19:04:49.375 22409-22409/com.hejunlin.videoclipD/VideoClip: trackIndex is 0;presentationTimeUs is 266666;sampleFlag is 0;sampleSize is 62812-18 19:04:49.376 22409-22409/com.hejunlin.videoclipD/VideoClip: trackIndex is 0;presentationTimeUs is 333333;sampleFlag is 0;sampleSize is 26712-18 19:04:49.376 22409-22409/com.hejunlin.videoclipD/VideoClip: trackIndex is 0;presentationTimeUs is 400000;sampleFlag is 0;sampleSize is 400312-18 19:04:49.377 22409-22409/com.hejunlin.videoclipD/VideoClip: trackIndex is 0;presentationTimeUs is 466666;sampleFlag is 0;sampleSize is 257512-18 19:04:49.377 22409-22409/com.hejunlin.videoclipD/VideoClip: trackIndex is 0;presentationTimeUs is 533333;sampleFlag is 0;sampleSize is 136412-18 19:04:49.378 22409-22409/com.hejunlin.videoclipD/VideoClip: trackIndex is 0;presentationTimeUs is 600000;sampleFlag is 0;sampleSize is 301912-18 19:04:49.379 22409-22409/com.hejunlin.videoclipD/VideoClip: trackIndex is 0;presentationTimeUs is 666666;sampleFlag is 0;sampleSize is 459512-18 19:04:49.379 22409-22409/com.hejunlin.videoclipD/VideoClip: trackIndex is 0;presentationTimeUs is 733333;sampleFlag is 0;sampleSize is 3689... 省略log12-18 19:04:49.467 22409-22409/com.hejunlin.videoclipD/VideoClip: AudioSampleTime is 4266712-18 19:04:49.468 22409-22409/com.hejunlin.videoclipD/VideoClip: trackIndex is 1;presentationTimeUs is 200533312-18 19:04:49.469 22409-22409/com.hejunlin.videoclipD/VideoClip: trackIndex is 1;presentationTimeUs is 204800012-18 19:04:49.469 22409-22409/com.hejunlin.videoclipD/VideoClip: trackIndex is 1;presentationTimeUs is 209066612-18 19:04:49.470 22409-22409/com.hejunlin.videoclipD/VideoClip: trackIndex is 1;presentationTimeUs is 213333312-18 19:04:49.470 22409-22409/com.hejunlin.videoclip... 省略logD/VideoClip: trackIndex is 1;presentationTimeUs is 12032000
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