Android(MediaScanner)多媒体扫描过程

1、Android多媒体扫描过程(AndroidMediaScannerProcess卜面是系统图MediaScannerReceiver会在任何的ACTION_BOOT_COMPLETED,ACTION_MEDIA_MOUNTED或ACTION_MEDIA_SCANNER_SCAN_FIL意图(intent)发出的时候启动。因为解析媒体文件的元数据或许会需要很长时间，所以MediaScannerReceiver会启动MediaScannerService。MediaScannerService调用一个公用类MediaScanner去处理真正的工作。MediaScannerReceiver维持两种

2、扫描目录：一种是内部卷(internalvolume)指向$(ANDROID_ROOT)/media.另一种是外部卷(externalvolume)指向$(EXTERNAL_STORAGE).扫描和解析工作位于JAVA层和C+层。JAVA层是启动器。MediaScanner扫描所有目录，如下步骤：1 .JAVA层初始化在这一步骤中，它会根据目录是在内部卷还是外部卷打开不同的数据库。2 .Java层预扫描首先清除文件和播放列表的缓存条目。然后根据MediaProvider返回的请求结果生成新文件和播放列表缓存条目。3 .C+层处理目录列举出所有文件和特定的所有子目录(如果子目录包含一个.nome

3、dia隐藏文件，则不会被列举出来。)。被列举的文件是根据文件扩展来判断文件是否被支持。如果支持这种文件扩展，C+层就会回调到JAVA层扫描文件。这种扩展就会被扫描到MediaFile.java中列出。下面是支持的文件扩展列表。/*Audio*/addFileType("MP3",FILE_TYPE_MP3,"audio/mpeg");addFileType("M4A",FILE_TYPE_M4A,"audio/mp4");addFileType("WAV",FILE_TYPE_WAV,"

4、;audio/x-wav");addFileType("AMR",FILE_TYPE_AMR,"audio/amr");addFileType("AWB",FILE_TYPE_AWB,"audio/amr-wb");addFileType("WMA",FILE_TYPE_WMA,"audio/x-ms-wma");addFileType("OGG",FILE_TYPE_OGG,"application/ogg");addFil

5、eType("MID",FILE_TYPE_MID,"audio/midi");addFileType("XMF",FILE_TYPE_MID,"audio/midi");addFileType("RTTTL”,FILE_TYPE_MID,"audio/midi");addFileType("SMF",FILE_TYPE_SMF,"audio/sp-midi");addFileType("IMY",FILE_TYPE_IMY&

6、quot;audio/imelody");/*Video*/addFileType("MP4",FILE_TYPE_MP4,"video/mp4");addFileType("M4V",FILE_TYPE_M4V,"video/mp4");addFileType("3GP",FILE_TYPE_3Gppvideo/3gpp");addFileType("3GPP",FILE_TYPE_3GPPvideo/3gpp");addFileType(&q

7、uot;3G2",FILE_TYPE_3GPP2,"videc3gpp2");addFileType("3GPP2",FILE_TYPE_3GPP2,"vide3gpp2");addFileType("WMV",FILE_TYPE_WMV,"video/x-ms-wmv");/*Image*/addFileType("JPG",FILE_TYPE_JPEG,"image/jpeg");addFileType("JPEG",FI

8、LE_TYPE_JPEG,"image/jpeg");addFileType("GIF",FILE_TYPE_GIF,"image/gif");addFileType("PNG",FILE_TYPE_PNG,"image/png");addFileType("BMP",FILE_TYPE_BMP"image/x-ms-bmp");addFileType("WBMP",FILE_TYPE_WBMP"image/vnd.wap.w

9、bmp");/*AudioPlayList*/addFileType("M3U",FILE_TYPE_M3U,"audio/x-mpegurl");addFileType("PLS",FILE_TYPE_PLS,"audio/x-scpls");addFileType("WPL",FILE_TYPE_WPL,"application/vnd.ms-wpl");4 .Java层扫描文件a)Java层开始文件首先它忽如一些MacOS和WindowsMediaPlayer

10、特殊的文件。然后它会查看被扫描的文件是否已经存在于缓存条目中，如果存在，它会检查文件上次修改的时间是否改变。最后它返回该文件是否需要进一步处理的结果。如果不需要，接下来的两步不会执行。b)C+层扫描文件不是所有的文件都需要交给C+层解析成元数据。只有下面的文件类型会被解析，注意，这里不处理image文件。if(mFileType=MediaFile.FILE_TYPE_MP3|mFileType=MediaFile.FILE_TYPE_MP4|mFileType=MediaFile.FILE_TYPE_M4A|mFileType=MediaFile.FILE_TYPE_3GPP|mFileTy

11、pe=MediaFile.FILE_TYPE_3GPP2|mFileType=MediaFile.FILE_TYPE_OGG|mFileType=MediaFile.FILE_TYPE_MID|mFileType=MediaFile.FILE_TYPE_WMA)复制代码对于被解析的元数据信息，C+层会回调到JAVA层白hhandleStringTag。Java层会记录它的name/value信息。c)Java层结束文件最后根据上一步解析出的值，Java层会更新相应的MeidaProvider产生的数据库表。5 .Java层发送扫描到目前为止，所有文件已经被扫描，它最后会检查文件和播放列表缓存条

12、目，看是否所有项仍然存在于文件系统。如果有空条目，则会从数据库中删除。这样它能够保持数据库和文件系统的一致性。其他的应用程序通过接收MediaScannerService发出的ACTION_MEDIA_SCANNER_STARTE讶口ACTION_MEDIA_SCANNER_FINISHEDT图能够知道什么时候扫描操作开始和结束。MediaScanner之所以拿MediaScanner开刀因为想借用系统的MediaScan工具通过Intent直接调用系统的步骤1 .下载并安装Git过程略网络上很多2 .得到该功能的模块地址并使用Git下载之地址：git:android.git.kernel.o

13、rg/platform/packages/providers/MediaProvider.git3 .分析源代码：-AndroidManifest.xml:各组件属性描述文件-MediaProvider:extendsContentProvider使用SQLiteDatabase保存查询数据action="content:/media"-MediaScannerCursor.java-MediaScannerReceiver:extendsBroadcastReceiver用于接收指定Broadcast:BOOT_COMPLETEDMEDIA_MOUNTEDMEDIA_SC

14、ANNER_SCAN_FIL浒启动MediaScannerService开始扫描-MediaScannerService:extendsService执行具体的扫描工作-MediaThumbRequest4.鉴于并不打算自行实现多媒体扫描因此此次重点研究对象：MediaScannerReceiver5. MediaScannerReceiver代码Java代码1. publicclassMediaScannerReceiverextendsBroadcastReceiver2. (3. privatefinalstaticStringTAG="MediaScannerReceiver

15、"4.5. Override6. publicvoidonReceive(Contextcontext,Intentintent)7. Stringaction=intent.getAction();8. Uriuri=intent.getData();9. StringexternalStoragePath=Environment.getExternalStorageDirectory().getPath();10.11. if(action.equals(Intent.ACTION_BOOT_COMPLETED)12. /scaninternalstorage13. scan(c

16、ontext,MediaProvider.INTERNAL_VOLUME);14. else15. if(uri.getScheme().equals("file")16. /handleintentsrelatedtoexternalstorage17. Stringpath=uri.getPath();18. if(action.equals(Intent.ACTION_MEDIA_MOUNTED)&&19. externalStoragePath.equals(path)20. scan(context,MediaProvider.EXTERNAL_V

17、OLUME);21. elseif(action.equals(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE)&&22. path!=null&&path.startsWith(externalStoragePath+"/")23. scanFile(context,path);24. 25. 26. 29. privatevoidscan(Contextcontext,Stringvolume)30. Bundleargs=newBundle();31. args.putString("volume&

18、quot;,volume);32. context.startService(33. newIntent(context,MediaScannerService.class).putExtras(args);34. 35.36. privatevoidscanFile(Contextcontext,Stringpath)37. Bundleargs=newBundle();38. args.putString("filepath",path);39. context.startService(40. newIntent(context,MediaScannerService

19、.class).putExtras(args);41. 42. 6 .根据以上代码得知:-当系统启动完毕会扫描一次-当ACTION_MEDIA_MOUNTEDACTION_MEDIA_SCANNER_SCAN_FILE也会扫描7 .如何调用系统MediaScanner进行扫描-通过Intent.ACTION_MEDIA_MOUNTED进行全扫描Java代码1. publicvoidallScan()2. sendBroadcast(newIntent(Intent.ACTION_MEDIA_MOUNTED,Uri.parse("file:/"3. +Environment.

20、getExternalStorageDirectory();4. -通过Intent.ACTION_MEDIA_SCANNER_SCAN_FILE扫描某个文件Java代码1. publicvoidfileScan(StringfName)2. Uridata=Uri.parse("file:/"+fName);3. sendBroadcast(newIntent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE,data);4. 补充：上述方法是不支持对文件夹的即：Uridata必须是文件的Uri如果是文件夹的其不会起作用的切记!-如何扫描某文件夹

21、下所有文件难道就不可以么？当然不借助于Intent.ACTION_MEDIA_SCANNER_SCAN_FILE我们可以这么做：取出该文件夹下的所有子文件如其是文件且类型符合条件就取出该文件目录以Intent.ACTION_MEDIA_SCANNER_SCAN_FILE方式发送至MediaScannerReceiver若其为文件夹则迭代查询之故实现为：Java代码1. publicvoidfileScan(Stringfile)2. Uridata=Uri.parse("file:/"+file);3.4. Log.d("TAG","file:

22、"+file);5. sendBroadcast(newIntent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE,data);6. 7.8. publicvoidfolderScan(Stringpath)9. Filefile=newFile(path);10.11. if(file.isDirectory()12. Filearray=file.listFiles();13.14. for(inti=0;i<array.length;i+)15. Filef=arrayi;16.17. if(f.isFile()/FILETYPE18. St

23、ringname=f.getName();19.20. if(name.contains(".mp3")21. fileScan(f.getAbsolutePath();22. 23. 24. else/FOLDERTYPE25.folderScan(f.getAbsolutePath();26. 27. 28. 29. 8.鉴于多数人并不关心其原理仅关系如何使用故总结如下:-扫描全部我猜测其在效率方面可能有点副作用Java代码1.publicvoidsystemScan()2.sendBroadcast(newIntent(Intent.ACTION_MEDIA_MOUN

24、TED,Uri.parse("file:/"3.+Environment.getExternalStorageDirectory();4.扫描某个文件参数：填入该文件的路径Java代码1.publicvoidfileScan(Stringfile)2.Uridata=Uri.parse("file:/"+file);3.4.sendBroadcast(newIntent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE,data);5.-扫描文件夹参数：填入该文件夹路径Java代码1.publicvoidfileScan(Str

25、ingfile)2.Uridata=Uri.parse("file:/"+file);3.4.sendBroadcast(newIntent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE,data);7.publicvoidfolderScan(Stringpath)8. Filefile=newFile(path);9.10. if(file.isDirectory()11. Filearray=file.listFiles();12.13. for(inti=0;i<array.length;i+)14. Filef=arrayi;1

26、5.16. if(f.isFile()/FILETYPE17. Stringname=f.getName();18.19. if(name.contains(".mp3")20. fileScan(f.getAbsolutePath();21. 22. 23. else/FOLDERTYPE24. folderScan(f.getAbsolutePath();25. 26. 27. 28. 终于结束了看似简单的东西研究起来还是挺复杂的!AndroidMediaScannerMechanismAnalyzeArchitectureFigure2-1AsFigure2-1.Me

27、diaScannerReciverstartupatanytimewherereceiveintentACTION_BOOT_COMPLETED,ACTION_MEDIA_MOUNTEDorACTION_MEDIA_SCANNER_SCAN_FILE.Causeonthatspendlongtimetoprocessthemediametadata,sothatMediaScannerReceiverwillcallupMediaScannerService.MediaScannerServiceinvokeapublicclasswhichnamedMediaScannertodothesc

28、anwork,MediaScannerhandlethemediadatabasewithapublicclasswhichnamedMediaProviderMediaScannerReciversupporttwotypesofthefolder:1.internalvolume,pointto$(ANDROID_ROOT)/media.2.Externalvolume,point$(EXTERNAL_STORAGE).ScannerActionACTION_BOOT_COMPLETEDpublicstaticfinalStringACTION_BOOT_COMPLETEDBroadcas

29、tAction:Thisisbroadcastonce,afterthesystemhasfinishedbooting.Itcanbeusedtoperformapplication-specificinitialization,suchasinstallingalarms.YoumustholdtheRECEIVE_BOOT_COMPLETEDpermissioninordertoreceivethisbroadcast.Thisisaprotectedintentthatcanonlybesentbythesystem.ConstantValue:"ent

30、.action.BOOT_COMPLETED"ACTION_MEDIA_MOUNTEDpublicstaticfinalStringACTION_MEDIA_MOUNTEDBroadcastAction:Externalmediaispresentandmountedatitsmountpoint.ThepathtothemountpointfortheremovedmediaiscontainedintheIntent.mDatafield.TheIntentcontainsanextrawithname"read-only"andBooleanvaluetoi

31、ndicateifthemediawasmountedreadonly.ConstantValue:"ent.action.MEDIA_MOUNTED"ACTION_MEDIA_SCANNER_SCAN_FILE.publicstaticfinalStringACTION_MEDIA_SCANNER_SCAN_FILEBroadcastAction:Requestthemediascannertoscanafileandaddittothemediadatabase.ThepathtothefileiscontainedintheIntent.mDat

32、afield.ConstantValue:"ent.action.MEDIA_SCANNER_SCAN_FILE"AndroidMediaScannerReceiverWecanfindthesourcefilewithpathanydroid/packages/providers/MediaProvider/src/com/android/providers/media/MediaScannerReceiver.javapublicclassMediaScannerReceiverextendsBroadcastReceiverOverridepub

33、licvoidonReceive(Contextcontext,Intentintent)if(action.equals(Intent.ACTION_BOOT_COMPLETED)/scaninternalstoragescan(context,MediaProvider.INTERNAL_VOLUME);elseif(uri.getScheme().equals("file")/handleintentsrelatedtoexternalstorageStringpath=uri.getPath();if(action.equals(Intent.ACTION_MEDI

34、A_MOUNTED)&&externalStoragePath.equals(path)scan(context,MediaProvider.EXTERNAL_VOLUME);elseif(action.equals(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE)&&path!=null&&path.startsWith(externalStoragePath+"/")scanFile(context,path);privatevoidscan(Contextcontext,Stringvolum

35、e)Bundleargs=newBundle();args.putString("volume",volume);context.startService(newIntent(context,MediaScannerService.class).putExtras(args);privatevoidscanFile(Contextcontext,Stringpath)Bundleargs=newBundle();args.putString("filepath",path);context.startService(newIntent(context,M

36、ediaScannerService.class).putExtras(args);BroadcasReceiver7MediaScannerHeceiuer+onReceieO:void-scanO：void-scanFileQ:voidFigure4-1Asthesourcecodes,andFigure4-1,therearetwodifferentmediadatabaseinthesystem,istheinternalstorage,theotheristheexternalstorage.Finally,theycallthemethodstartService()tostart

37、theMediaScannerService.AndroidMediaScannerServiceWecanfindthesourcefilewithpath/android/packages/providers/MediaProvider/src/com/android/providers/media/MediaScannerService.java.publicvoidonCreate()Threadthr=newThread(null,this,"MediaScannerService");thr.start();publicintonStartCommand(Int

38、entintent,intflags,intstartId)Messagemsg=mServiceHandler.obtainMessage();mServiceHandler.sendMessage(msg);returnService.START_REDELIVER_INTENT;publicvoidrun()mServiceHandler=newServiceHandler();)privatefinalclassServiceHandlerextendsHandler(OverridepublicvoidhandleMessage(Messagemsg)(if(filePath!=nu

39、ll)Uriuri=scanFile(filePath,arguments.getString("mimetype");)elsescan(directories,volume);)privatevoidscan(Stringdirectories,StringvolumeName)MediaScannerscanner=createMediaScanner();scanner.scanDirectories(directories,volumeName);)privateUriscanFile(Stringpath,StringmimeType)MediaScanners

40、canner=createMediaScanner();returnscanner.scanSingleFile(path,volumeName,mimeType);)ServiceHandlerMediaScannerService+handleMessage():void-mBinder:IMediaScannerService.Stub«interface»Runnable- openDatabase():void- closeDatabase():void- createMediaScanner():void- scan():void- scanFile():voi

41、d+onCreate():void+onStart():void+onDestroy():gid+run():void+onBindf):voidFigure5-1Androidapplicationmaybeblockwithinvokingservice,genericcreateathreadtorunatthebackend.First,mediaservicecallonCreate()tostarttheserviceifitisnotexist,thencreateathreadandrunthread.start()tocalltherunnablemethodwhichhas

42、implementedwiththerun().Intherun(),invokeainternalclassnamedServiceHandlertoscanfile.Inthemethodscan()andscanFile(),theyallinvokeapublicclassnamedMediaScannerwhomhasmethodnamedcreateMediaScanner()toprocessmetadataandmediadabase.AndroidMediaScannerWecanfindtherelatefileswithpathandroid/frameworks/bas

43、e/media/java/android/media,Figure6-1javacodesfile:/android/frameworks/base/media/java/android/media/MediaScanner.javapublicvoidscanDirectories(String口directories,StringvolumeName)for(inti=0;i<directories.length;i+)processDirectory(directoriesi,MediaFile.sFileExtensions,mClient);publicvoidscanFile

44、(Stringpath,longlastModified,longfileSize)/Thisisthecallbackfuntionfromnativecodes./Log.v(TAG,"scanFile:"+path);doScanFile(path,null,lastModified,fileSize,false);publicvoidscanFile(Stringpath,StringmimeType,longlastModified,longfileSize)doScanFile(path,mimeType,lastModified,fileSize,false)

45、;publicUridoScanFile(Stringpath,StringmimeType,longlastModified,longfileSize,booleanscanAlways)if(isMetadataSupported(mFileType)processFile(path,mimeType,this);elseif(MediaFile.isImageFileType(mFileType)/weusedtocomputethewidthandheightbutit'snotworthitresult=endFile(entry,ringtones,notification

46、s,alarms,music,podcasts);privateUriendFile(FileCacheEntryentry,booleanringtones,booleannotifications,booleanalarms,booleanmusic,booleanpodcasts)throwsRemoteExceptionmMediaProvider.insert()/mMediaProvider.update()privatenativevoidprocessDirectory(Stringpath,Stringextensions,MediaScannerClientclient);

47、privatenativevoidprocessFile(Stringpath,StringmimeType,MediaScannerClientclient);c+codesfile:/android/frameworks/base/media/jni/android_media_MediaScanner.cppstaticvoidandroid_media_MediaScanner_processDirectory(JNIEnv*env,jobjectthiz,jstringpath,jstringextensions,jobjectclient)MediaScanner*mp=(Medi

48、aScanner*)env->GetIntField(thiz,fields.context);MyMediaScannerClientmyClient(env,client);mp->processDirectory(pathStr,extensionsStr,myClient,ExceptionCheck,env);staticvoidandroid_media_MediaScanner_processFile(JNIEnv*env,jobjectthiz,jstringpath,jstringmimeType,jobjectclient)MediaScanner*mp=(Me

49、diaScanner*)env->GetIntField(thiz,fields.context);MyMediaScannerClientmyClient(env,client);mp->processFile(pathStr,mimeTypeStr,myClient);file:/android/external/opencore/android/mediascanner.cppstatus_tMediaScanner:processDirectory(constchar*path,constchar*extensions,MediaScannerClient&clie

50、nt,ExceptionCheckexceptionCheck,void*exceptionEnv)result=doProcessDirectory(pathBuffer,pathRemaining,extensions,client,exceptionCheck,exceptionEnv);status_tMediaScanner:doProcessDirectory(char*path,intpathRemaining,constchar*extensions,MediaScannerClient&client,ExceptionCheckexceptionCheck,void*

51、exceptionEnv)client.scanFile(path,statbuf.st_mtime,statbuf.st_size);status_tMediaScanner:processFile(constchar*path,constchar*mimeType,MediaScannerClient&client)status_tresult=PVMFSuccess;interror=0;InitializeForThread();OSCL_TRY(error,client.setLocale(mLocale);client.beginFile();/LOGD("pro

52、cessFile%smimeType:%sn",path,mimeType);constchar*extension=strrchr(path,'.');if(extension&&(strcasecmp(extension,".mp3")=0|strcasecmp(extension,".aac")=0)/Bothmp3andaacfilesuseID3tagstoholdmetadataresult=parseID3Tag(path,client);elseif(extension&&(str

53、casecmp(extension,".mp4")=0|strcasecmp(extension,".m4a")=0|strcasecmp(extension,".3gp")=0|strcasecmp(extension,".3gpp")=0|strcasecmp(extension,".3g2")=0|strcasecmp(extension,".m4b")=0|strcasecmp(extension,".3gpp2")=0)result=parseM

54、P4(path,client);elseif(extension&&strcasecmp(extension,".ogg")=0)result=parseOgg(path,client);elseif(extension&&(strcasecmp(extension,".mid")=0|strcasecmp(extension,".smf")=0|strcasecmp(extension,".imy")=0)result=parseMidi(path,client);elseif(e

55、xtension&&(strcasecmp(extension,".wma")=0|strcasecmp(extension,".wmv")=0|strcasecmp(extension,".asf")=0|strcasecmp(extension,".amr")=0|strcasecmp(extension,".wav")=0|strcasecmp(extension,".awb")=0)result=parseASF(path,client);elsere

56、sult=PVMFFailure;client.endFile();)；OSCL_FIRST_CATCH_ANY(error,LOGV("OSCL_LEAVEhappenedinprocessFileExitwithfailure");returnPVMFFailure);returnresult;AsFigure6-1,IfscanDirectory()hascalledbyMediaScannerService,itwillinvokec+llibrarylibmedia_jnimethodprocessDiretorys()byJNImechanism,thenpro

57、cessDiretorys()invokeJAVAclassMyMediaScannerClientbyJNI,Finaly,endFile()usetoinsertorupdatethedatabase原文地址修改AndroidMediaScanner的扫描路径对Android稍有熟悉的人都知道，AndroidMediaScanner只对SD卡上的媒体文件进行扫描。其扫描的策略，请参考«AndroidMediaScannerProcess»o假如我们的硬件平台上面没有提供SD卡槽，难道Android就不能进行对媒体文件播放了吗？当然不是的，否则Android系统将不会成为

58、一个完善的Frameworko本文结合本人的经验介绍一下，怎样修改多媒体文件的扫描路径。根据AndroidMediaScannerProcess»的介绍我们可以知道，Androidscanner扫描媒体完成之后，会把媒体文件存放在数据库中，由MediaProvider为上层的应用程序提供服务。经过研究Mediascanner的代码发现，他的扫描路径为android.os.Environment.EXTERNAL_STORAGE_DIRECTORY定义该变量文件位于：frameworks/base/core/java/android/os/Environment.java默认情况下，A

59、ndroid将会搜索/sddisk目录：privatestaticfinalFileEXTERNAL_STORAGE_DIRECTORY=getDirectory("EXTERNAL_STORAGE","/sddisk");为了让其进行搜索我们自定义的路径，可以修改该变量的定义，加入我们希望扫描/external目录。代码修改如下：privatestaticfinalFileEXTERNAL_STORAGE_DIRECTORY=getDirectory("EXTERNAL_STORAGE","/external");这本AAndroidMediaScanner将会搜索/external目录来查找媒体文件。下一步我们需要保证这个文件一定要存在，我们需要修改init.rc文件。增加如下的定义：mkdir/external0777systemsystem这样在开机的时候，如果/external目录不存在，则会创建一个。如果已经存在，则不会有任何动作。另外怎样触发MediaScanner?根据Andr