Android多媒体文件扫描流程

插入u盘后，系统会发送广播android.intent.action.MEDIA_MOUNTED

位于

packages/providers/MediaProvider/src/com/android/providers/media/MediaScannerService.java

MediaScannerService可以接收开机广播和u盘插入广播，收到广播后执行scan方法，将文件或文件夹路径存储到Bundle，并启动MediaScannerService，我们看MediaScannerService中ServiceHandler的代码

private final class ServiceHandler extends Handler
{
@Override
public void handleMessage(Message msg)
{
Bundle arguments = (Bundle) msg.obj;
String filePath = arguments.getString("filepath");//单个文件
String path = arguments.getString("path");//文件目录

try {
if (filePath != null) {
IBinder binder = arguments.getIBinder("listener");
IMediaScannerListener listener =
(binder == null ? null : IMediaScannerListener.Stub.asInterface(binder));
Uri uri = null;
try {
uri = scanFile(filePath, arguments.getString("mimetype"));//扫描单个文件
} catch (Exception e) {
Log.e(TAG, "Exception scanning file", e);
}
if (listener != null) {
listener.scanCompleted(filePath, uri);
}
} else {
String volume = arguments.getString("volume");
String[] directories = null;

if (MediaProvider.INTERNAL_VOLUME.equals(volume)) {
// scan internal media storage
directories = new String[] {
Environment.getRootDirectory() + "/media",
};
}
else if (MediaProvider.EXTERNAL_VOLUME.equals(volume)) {
// scan external storage volumes
if (path == null) {
directories = mExternalStoragePaths;
} else if (path.startsWith("/mnt/usb_storage")) {
directories = new String[] {path};//{"/mnt/usb_storage"};
} else {
directories = new String[] {path};
}
}

if (directories != null) {
if (true) Log.d(TAG, "start scanning volume " + volume + ": "
+ Arrays.toString(directories));
scan(directories, volume);//扫描文件列表
if (true) Log.d(TAG, "done scanning volume " + volume);
}
}
} catch (Exception e) {
Log.e(TAG, "Exception in handleMessage", e);
}

stopSelf(msg.arg1);
}
};

可以看到代码会调用scan或者scanFile扫描

private void scan(String[] directories, String volumeName) {
Uri uri = Uri.parse("file://" + directories[0]);
// don't sleep while scanning
mWakeLock.acquire();

try {
ContentValues values = new ContentValues();
values.put(MediaStore.MEDIA_SCANNER_VOLUME, volumeName);
Uri scanUri = getContentResolver().insert(MediaStore.getMediaScannerUri(), values);

sendBroadcast(new Intent(Intent.ACTION_MEDIA_SCANNER_STARTED, uri));

try {
if (volumeName.equals(MediaProvider.EXTERNAL_VOLUME)) {
openDatabase(volumeName);
}

MediaScanner scanner = createMediaScanner();
if(directories!=null){
scanner.scanDirectories(directories, volumeName);
}
} catch (Exception e) {
Log.e(TAG, "exception in MediaScanner.scan()", e);
}

getContentResolver().delete(scanUri, null, null);

} finally {
sendBroadcast(new Intent(Intent.ACTION_MEDIA_SCANNER_FINISHED, uri));
mWakeLock.release();
}
}

private Uri scanFile(String path, String mimeType) {
String volumeName = MediaProvider.EXTERNAL_VOLUME;
openDatabase(volumeName);
MediaScanner scanner = createMediaScanner();
try {
// make sure the file path is in canonical form
String canonicalPath = new File(path).getCanonicalPath();
return scanner.scanSingleFile(canonicalPath, volumeName, mimeType);
} catch (Exception e) {
Log.e(TAG, "bad path " + path + " in scanFile()", e);
return null;
}
}

下一步进入到MediaScanner.java，文件在

frameworks/base/media/java/android/media/MediaScanner.java

下面是扫描单个文件的代码

// this function is used to scan a single file
public Uri scanSingleFile(String path, String volumeName, String mimeType) {
try {
initialize(volumeName);
prescan(path, true);

File file = new File(path);
if (!file.exists()) {
return null;
}

// lastModified is in milliseconds on Files.
long lastModifiedSeconds = file.lastModified() / 1000;

// always scan the file, so we can return the content://media Uri for existing files
return mClient.doScanFile(path, mimeType, lastModifiedSeconds, file.length(),
false, true, MediaScanner.isNoMediaPath(path));
} catch (RemoteException e) {
Log.e(TAG, "RemoteException in MediaScanner.scanFile()", e);
return null;
}
}
//初始化默认的uri
private void initialize(String volumeName) {
mMediaProvider = mContext.getContentResolver().acquireProvider("media");

mAudioUri = Audio.Media.getContentUri(volumeName);
mVideoUri = Video.Media.getContentUri(volumeName);
mImagesUri = Images.Media.getContentUri(volumeName);
mThumbsUri = Images.Thumbnails.getContentUri(volumeName);
mFilesUri = Files.getContentUri(volumeName);
mFilesUriNoNotify = mFilesUri.buildUpon().appendQueryParameter("nonotify", "1").build();

if (!volumeName.equals("internal")) {
// we only support playlists on external media
mProcessPlaylists = true;
mProcessGenres = true;
mPlaylistsUri = Playlists.getContentUri(volumeName);

mCaseInsensitivePaths = true;
}
}
//扫描预处理，暂时不知道做什么用
private void prescan(String filePath, boolean prescanFiles) throws RemoteException {
Cursor c = null;
String where = null;
String[] selectionArgs = null;

if (mPlayLists == null) {
mPlayLists = new ArrayList<FileEntry>();
} else {
mPlayLists.clear();
}

if (filePath != null) {
// query for only one file
where = MediaStore.Files.FileColumns._ID + ">?" +
" AND " + Files.FileColumns.DATA + " like '"+filePath+"%' ";
selectionArgs = new String[] { "" };
} else {
where = MediaStore.Files.FileColumns._ID + ">?";
selectionArgs = new String[] { "" };
}
if (DEBUG_MEDIASCANNER)
Log.d(TAG,"-----------enter prescan,filePath = "+filePath+"where = "+where);

// Tell the provider to not delete the file.
// If the file is truly gone the delete is unnecessary, and we want to avoid
// accidentally deleting files that are really there (this may happen if the
// filesystem is mounted and unmounted while the scanner is running).
Uri.Builder builder = mFilesUri.buildUpon();
builder.appendQueryParameter(MediaStore.PARAM_DELETE_DATA, "false");
MediaBulkDeleter deleter = new MediaBulkDeleter(mMediaProvider, mPackageName,
builder.build());

// Build the list of files from the content provider
try {
if (prescanFiles) {
// First read existing files from the files table.
// Because we'll be deleting entries for missing files as we go,
// we need to query the database in small batches, to avoid problems
// with CursorWindow positioning.
long lastId = Long.MIN_VALUE;
Uri limitUri = mFilesUri.buildUpon().appendQueryParameter("limit", "1000").build();
mWasEmptyPriorToScan = true;

while (true) {
selectionArgs[0] = "" + lastId;
if (c != null) {
c.close();
c = null;
}
c = mMediaProvider.query(mPackageName, limitUri, FILES_PRESCAN_PROJECTION,
where, selectionArgs, MediaStore.Files.FileColumns._ID, null);
if (c == null) {
break;
}

int num = c.getCount();

if (num == 0) {
break;
}
mWasEmptyPriorToScan = false;
while (c.moveToNext()) {
long rowId = c.getLong(FILES_PRESCAN_ID_COLUMN_INDEX);
String path = c.getString(FILES_PRESCAN_PATH_COLUMN_INDEX);
int format = c.getInt(FILES_PRESCAN_FORMAT_COLUMN_INDEX);
long lastModified = c.getLong(FILES_PRESCAN_DATE_MODIFIED_COLUMN_INDEX);
lastId = rowId;

// Only consider entries with absolute path names.
// This allows storing URIs in the database without the
// media scanner removing them.
if (path != null && path.startsWith("/")) {
boolean exists = false;
try {
exists = Libcore.os.access(path, libcore.io.OsConstants.F_OK);
} catch (ErrnoException e1) {
}
if (!exists && !MtpConstants.isAbstractObject(format)) {
// do not delete missing playlists, since they may have been
// modified by the user.
// The user can delete them in the media player instead.
// instead, clear the path and lastModified fields in the row
MediaFile.MediaFileType mediaFileType = MediaFile.getFileType(path);
int fileType = (mediaFileType == null ? 0 : mediaFileType.fileType);

if (!MediaFile.isPlayListFileType(fileType)) {
deleter.delete(rowId);
if (path.toLowerCase(Locale.US).endsWith("/.nomedia")) {
deleter.flush();
String parent = new File(path).getParent();
mMediaProvider.call(mPackageName, MediaStore.UNHIDE_CALL,
parent, null);
}
}
}
}
}
}
}
}
finally {
if (c != null) {
c.close();
}
deleter.flush();
}

// compute original size of images
mOriginalCount = 0;
c = mMediaProvider.query(mPackageName, mImagesUri, ID_PROJECTION, null, null, null, null);
if (c != null) {
mOriginalCount = c.getCount();
c.close();
}
}

下面是真正的扫描实现

public Uri doScanFile(String path, String mimeType, long lastModified,
long fileSize, boolean isDirectory, boolean scanAlways, boolean noMedia) {
Uri result = null;
//            long t1 = System.currentTimeMillis();
try {
FileEntry entry = beginFile(path, mimeType, lastModified,
fileSize, isDirectory, noMedia);
if (path.startsWith("/mnt/usb_storage"))
mIsUsbStorage =true;
else
mIsUsbStorage =false;
// if this file was just inserted via mtp, set the rowid to zero
// (even though it already exists in the database), to trigger
// the correct code path for updating its entry
if (mMtpObjectHandle != 0) {
entry.mRowId = 0;
}
// rescan for metadata if file was modified since last scan
if (entry != null && (entry.mLastModifiedChanged || scanAlways)) {
if (noMedia) {
result = endFile(entry, false, false, false, false, false);
} else {
String lowpath = path.toLowerCase(Locale.ROOT);
boolean ringtones = (lowpath.indexOf(RINGTONES_DIR) > 0);
boolean notifications = (lowpath.indexOf(NOTIFICATIONS_DIR) > 0);
boolean alarms = (lowpath.indexOf(ALARMS_DIR) > 0);
boolean podcasts = (lowpath.indexOf(PODCAST_DIR) > 0);
boolean music = (lowpath.indexOf(MUSIC_DIR) > 0) ||
(!ringtones && !notifications && !alarms && !podcasts);
//判断是否是音视频格式，来决定下面是否对其扫描。
boolean isaudio = MediaFile.isAudioFileType(mFileType);
boolean isvideo = MediaFile.isVideoFileType(mFileType);
boolean isimage = MediaFile.isImageFileType(mFileType);

if (isaudio || isvideo || isimage) {
if (mExternalIsEmulated && path.startsWith(mExternalStoragePath)) {
// try to rewrite the path to bypass the sd card fuse layer
String directPath = Environment.getMediaStorageDirectory() +                                 path.substring(mExternalStoragePath.length());
File f = new File(directPath);
if (f.exists()) {
path = directPath;
}
}
}
// we only extract metadata for audio and video files
if (isaudio /*|| isvideo */)
{
//jni方法调用，真正的扫描开始
processFile(path, mimeType, this);
}
//if (isimage) {
//    processImageFile(path);
//}
result = endFile(entry, ringtones, notifications, alarms, music, podcasts);
}
}
} catch (RemoteException e) {
Log.e(TAG, "RemoteException in MediaScanner.scanFile()", e);
}
//            long t2 = System.currentTimeMillis();
//            Log.v(TAG, "scanFile: " + path + " took " + (t2-t1));
return result;
}

在路径frameworks/base/media/java/android/media/MediaFile.java

可以找到音视频扫描所支持的类型。

public class MediaFile {
39
40     // Audio file types
41     public static final int FILE_TYPE_MP3     = 1;
42     public static final int FILE_TYPE_M4A     = 2;
43     public static final int FILE_TYPE_WAV     = 3;
44     public static final int FILE_TYPE_AMR     = 4;
45     public static final int FILE_TYPE_AWB     = 5;

..........................
static {
205         addFileType("MP3", FILE_TYPE_MP3, "audio/mpeg", MtpConstants.FORMAT_MP3);
206         addFileType("MP3", FILE_TYPE_MP3, "audio/lume", MtpConstants.FORMAT_MP3);
207         addFileType("MPGA", FILE_TYPE_MP3, "audio/mpeg", MtpConstants.FORMAT_MP3);
208         addFileType("M4A", FILE_TYPE_M4A, "audio/mp4", MtpConstants.FORMAT_MPEG);
............................

其中有一段代码

180     private static boolean isWMAEnabled() {
181     List<AudioDecoder> decoders = DecoderCapabilities.getAudioDecoders();
182    int count = decoders.size();
183    for (int i = 0; i < count; i++) {
184      AudioDecoder decoder = decoders.get(i);
//当下面条件成立才行
185   if (decoder == AudioDecoder.AUDIO_DECODER_WMA) {
186                 return true;
187             }
188         }
189         return false;
190     }
.......................
212         if (isWMAEnabled()) {
">213         addFileType("WMA", FILE_TYPE_WMA, "audio/x-ms-wma", MtpConstants.FORMAT_WMA);
214         }

WMA音频格式是Google的专利，所以想支持扫描wma格式，可以去grep “AUDIO_DECODER_WMA” -rn .

在frameworks/av/media/libmedia/MediaProfiles.cpp中

const char *defaultXmlFile = "/etc/media_profiles.xml"

在板级中device/XXX/XXXX/config/media_profiles.xml

<AudioDecoderCap name="wma" enabled="false"/>

将false改为true即可。

我们看一下英文说明

MediaScanner.processFile().
* - MediaScanner.processFile() calls one of several methods, depending on the type of the
*   file: parseMP3, parseMP4, parseMidi, parseOgg or parseWMA.
* - each of these methods gets metadata key/value pairs from the file, and repeatedly
*   calls native MyMediaScannerClient.handleStringTag, which calls back up to its Java
*   counterparts in this file.

大意就是，processFile会根据文件类型调用不用的方法，并由MyMediaScannerClient.handleStringTag回调

这段native方法可以在下面的文件目录找到

frameworks/base/media/jni/android_media_MediaScanner.cpp

static void
android_media_MediaScanner_processFile(
JNIEnv *env, jobject thiz, jstring path,
jstring mimeType, jobject client)
{
ALOGV("processFile");

// Lock already hold by processDirectory
MediaScanner *mp = getNativeScanner_l(env, thiz);
if (mp == NULL) {
jniThrowException(env, kRunTimeException, "No scanner available");
return;
}

if (path == NULL) {
jniThrowException(env, kIllegalArgumentException, NULL);
return;
}

const char *pathStr = env->GetStringUTFChars(path, NULL);
if (pathStr == NULL) {  // Out of memory
return;
}

const char *mimeTypeStr =
(mimeType ? env->GetStringUTFChars(mimeType, NULL) : NULL);
if (mimeType && mimeTypeStr == NULL) {  // Out of memory
// ReleaseStringUTFChars can be called with an exception pending.
env->ReleaseStringUTFChars(path, pathStr);
return;
}

MyMediaScannerClient myClient(env, client);
MediaScanResult result = mp->processFile(pathStr, mimeTypeStr, myClient);
if (result == MEDIA_SCAN_RESULT_ERROR) {
ALOGE("An error occurred while scanning file '%s'.", pathStr);
}
env->ReleaseStringUTFChars(path, pathStr);
if (mimeType) {
env->ReleaseStringUTFChars(mimeType, mimeTypeStr);
}
}

mp->processFile在路径

通过grep搜索发现，方法定义在文件frameworks/av/media/libmedia/MediaScanner.h

可以看到这是一个虚函数

virtual MediaScanResult processFile(
const char *path, const char *mimeType, MediaScannerClient &client) = 0;

虚函数定义如下：如果父类的函数（方法）根本没有必要或者无法实现，完全要依赖子类去实现的话，可以把此函数（方法）设为virtual 函数名=0 我们把这样的函数（方法）称为纯虚函数如果一个类包含了纯虚函数，称此类为抽象类。

我们接着往下跟，找到真正实现的地方

回到前一个jni

frameworks/base/media/jni/android_media_MediaScanner.cpp

这里面有实例化mediascanner的地方

static void
android_media_MediaScanner_native_setup(JNIEnv *env, jobject thiz)
{
ALOGV("native_setup");
MediaScanner *mp = new StagefrightMediaScanner;

if (mp == NULL) {
jniThrowException(env, kRunTimeException, "Out of memory");
return;
}

env->SetIntField(thiz, fields.context, (int)mp);
}

马上就能找到实例化的地方了，打开

frameworks/av/media/libstagefright/StagefrightMediaScanner.cpp

MediaScanResult StagefrightMediaScanner::processFile(
const char *path, const char *mimeType,
MediaScannerClient &client) {
ALOGV("processFile '%s'.", path);

client.setLocale(locale());
client.beginFile();
MediaScanResult result = processFileInternal(path, mimeType, client);
client.endFile();
return result;
}

MediaScanResult StagefrightMediaScanner::processFileInternal(
const char *path, const char *mimeType,
MediaScannerClient &client) {
const char *extension = strrchr(path, '.');

if (!extension) {
return MEDIA_SCAN_RESULT_SKIPPED;
}

//过滤支持的类型
if (!FileHasAcceptableExtension(extension)) {
return MEDIA_SCAN_RESULT_SKIPPED;
}

//根据扩展名调用不同的解析方法
if (!strcasecmp(extension, ".mid")
|| !strcasecmp(extension, ".smf")
|| !strcasecmp(extension, ".imy")
|| !strcasecmp(extension, ".midi")
|| !strcasecmp(extension, ".xmf")
|| !strcasecmp(extension, ".rtttl")
|| !strcasecmp(extension, ".rtx")
|| !strcasecmp(extension, ".ota")
|| !strcasecmp(extension, ".mxmf")) {
return HandleMIDI(path, &client);
}
//parse ape audio file
if (!strcasecmp(extension, ".ape")) {
return parseAPE(path, client);
}
sp<MediaMetadataRetriever> mRetriever(new MediaMetadataRetriever);

int fd = open(path, O_RDONLY | O_LARGEFILE);
status_t status;
if (fd < 0) {
// couldn't open it locally, maybe the media server can?
status = mRetriever->setDataSource(path);
} else {
status = mRetriever->setDataSource(fd, 0, 0x7ffffffffffffffL);
close(fd);
}

if (status) {
return MEDIA_SCAN_RESULT_ERROR;
}

const char *value;
if ((value = mRetriever->extractMetadata(
METADATA_KEY_MIMETYPE)) != NULL) {
status = client.setMimeType(value);
if (status) {
return MEDIA_SCAN_RESULT_ERROR;
}
}

android支持哪些音视频格式类型在FileHasAcceptableExtension（extension）函数中定义的

static bool FileHasAcceptableExtension(const char *extension) {
41     static const char *kValidExtensions[] = {
42         ".mp3", ".mp4", ".m4a", ".3gp", ".3gpp", ".3g2", ".3gpp2",
43         ".mpeg", ".ogg", ".mid", ".smf", ".imy", ".wma", ".aac",
44         ".wav", ".amr", ".midi", ".xmf", ".rtttl", ".rtx", ".ota",
2> 45         ".mkv", ".mka", ".webm", ".ts", ".fl", ".flac", ".mxmf",
.> 46         ".avi", ".mpeg", ".mpg", ".awb", ".mpga", ".wmv", ".flv", ".rm", ".rmvb", ".mov", ".vob", ".m4v", ".f4v", ".amv", ".dat"
47     };
48     static const size_t kNumValidExtensions =
49         sizeof(kValidExtensions) / sizeof(kValidExtensions[0]);
}> 50
51     for (size_t i = 0; i < kNumValidExtensions; ++i) {
52         if (!strcasecmp(extension, kValidExtensions[i])) {
53             return true;
54         }
55     }
56
57     return false;
58 }

如果想增加某种音频或者视频格式，需要做的就是两步

1、在kValidExtensions[] 数组中添加后缀名。如.dat

2、frameworks/base/media/java/android/media/MediaFile.java中添加public static final int FILE_TYPE_ABC = 数字;

addFileType(“DAT”, FILE_TYPE_DAT, “video/dat”);

android-4.4可以在相应的路径中mm 生成的frameworks.jar

android-5.1不能mm，必须make systemimage 重新烧录。