Android中如何获取视频文件的缩略图

欢迎访问我的个人博客阅读：http://androidfuture.com/blog/?p=195

在android中获取视频文件的缩略图有三种方法：

1.从媒体库中查询

2. android 2.2以后使用ThumbnailUtils类获取

3.调用jni文件，实现MediaMetadataRetriever类

三种方法各有利弊

第一种方法，新视频增加后需要SDCard重新扫描才能给新增加的文件添加缩略图，灵活性差，而且不是很稳定，适合简单应用

第二种方法，实现简单，但2.2以前的版本不支持

第三种方法，实现复杂，但比较灵活，推荐使用

下面给出三种方法的Demo

1.第一种方法：

public static Bitmap getVideoThumbnail(ContentResolver cr, String fileName) { Bitmap bitmap = null; BitmapFactory.Options options = new BitmapFactory.Options(); options.inDither = false; options.inPreferredConfig = Bitmap.Config.ARGB_8888; //select condition. String whereClause = MediaStore.Video.Media.DATA + ” = ‘” + fileName + “‘”; Log.v(TAG, “where = ” + whereClause); //colection of results. Cursor cursor = cr.query(MediaStore.Video.Media.EXTERNAL_CONTENT_URI, new String[] { MediaStore.Video.Media._ID }, whereClause, null, null); Log.v(TAG, “cursor = ” + cursor); if (cursor == null || cursor.getCount() == 0) { return null; } cursor.moveToFirst(); //image id in image table. String videoId = cursor.getString(cursor .getColumnIndex(MediaStore.Video.Media._ID)); Log.v(TAG, “videoId = ” + videoId); if (videoId == null) { return null; } cursor.close(); long videoIdLong = Long.parseLong(videoId); //via imageid get the bimap type thumbnail in thumbnail table. bitmap = MediaStore.Video.Thumbnails.getThumbnail(cr, videoIdLong, Images.Thumbnails.MICRO_KIND, options); Log.v(TAG, “bitmap = ” + bitmap); return bitmap; }

2. 第二种方法：

通过ThumbnailUtils的三种静态方法。

1. static Bitmap createVideoThumbnail(String filePath, int kind) //获取视频文件的缩略图，第一个参数为视频文件的位置，比如/sdcard/android123.3gp，而第二个参数可以为MINI_KIND或 MICRO_KIND最终和分辨率有关
2. static Bitmap extractThumbnail(Bitmap source, int width, int height, int options) //直接对Bitmap进行缩略操作，最后一个参数定义为OPTIONS_RECYCLE_INPUT ，来回收资源
3. static Bitmap extractThumbnail(Bitmap source, int width, int height) // 这个和上面的方法一样，无options选项

3. 第三种方法：

MediaMetadataRetriever是android中隐藏的一个类，开发者无法调用，只能实现一个相同的类来完成相关功能。

一种方式是修改android源码，将frameworks  MediaMetadataRetriever.java中@hide标签去掉,在current.xml中添加MediaMetadataRetriever到可用.重新编译frameworks,应用就可以调用到MediaMetadataRetriever这个类了…这样是不适合应用开发的。

推荐的方法是实现MediaMetadataRetriever类

第一步:首先需要下载JNI库：libmedia_jni.so

进入SDK的Tools目录下，运行DDMS，
在DDMS中的菜单栏中，执行Device–FileExplore,
在弹出的文件列表中选择: System-Lib-libmedia_jni.so
选中这个文件后， 在弹出的文件列表的又上脚执行PULL file from device,提取出libmedia_jni.so文件
在Eclipse中新建文件夹libs-armeabi-,在里面放入libmedia_jni.so文件

第二部：实现MediaMetadataRetriever

public class MediaMetadataRetriever

{

static {

System.loadLibrary(“media_jni”);

native_init();

}

// The field below is accessed by native methods

@SuppressWarnings(“unused”)

private int mNativeContext;

public MediaMetadataRetriever() {

native_setup();

}

/**

* Call this method before setDataSource() so that the mode becomes

* effective for subsequent operations. This method can be called only once

* at the beginning if the intended mode of operation for a

* MediaMetadataRetriever object remains the same for its whole lifetime,

* and thus it is unnecessary to call this method each time setDataSource()

* is called. If this is not never called (which is allowed), by default the

* intended mode of operation is to both capture frame and retrieve meta

* data (i.e., MODE_GET_METADATA_ONLY | MODE_CAPTURE_FRAME_ONLY).

* Often, this may not be what one wants, since doing this has negative

* performance impact on execution time of a call to setDataSource(), since

* both types of operations may be time consuming.

*

* @param mode The intended mode of operation. Can be any combination of

* MODE_GET_METADATA_ONLY and MODE_CAPTURE_FRAME_ONLY:

* 1. MODE_GET_METADATA_ONLY & MODE_CAPTURE_FRAME_ONLY:

*    For neither frame capture nor meta data retrieval

* 2. MODE_GET_METADATA_ONLY: For meta data retrieval only

* 3. MODE_CAPTURE_FRAME_ONLY: For frame capture only

* 4. MODE_GET_METADATA_ONLY | MODE_CAPTURE_FRAME_ONLY:

*    For both frame capture and meta data retrieval

*/

public native void setMode(int mode);

/**

* @return the current mode of operation. A negative return value indicates

* some runtime error has occurred.

*/

public native int getMode();

/**

* Sets the data source (file pathname) to use. Call this

* method before the rest of the methods in this class. This method may be

* time-consuming.

*

* @param path The path of the input media file.

* @throws IllegalArgumentException If the path is invalid.

*/

public native void setDataSource(String path) throws IllegalArgumentException;

/**

* Sets the data source (FileDescriptor) to use.  It is the caller’s

* responsibility to close the file descriptor. It is safe to do so as soon

* as this call returns. Call this method before the rest of the methods in

* this class. This method may be time-consuming.

*

* @param fd the FileDescriptor for the file you want to play

* @param offset the offset into the file where the data to be played starts,

* in bytes. It must be non-negative

* @param length the length in bytes of the data to be played. It must be

* non-negative.

* @throws IllegalArgumentException if the arguments are invalid

*/

public native void setDataSource(FileDescriptor fd, long offset, long length)

throws IllegalArgumentException;

/**

* Sets the data source (FileDescriptor) to use. It is the caller’s

* responsibility to close the file descriptor. It is safe to do so as soon

* as this call returns. Call this method before the rest of the methods in

* this class. This method may be time-consuming.

*

* @param fd the FileDescriptor for the file you want to play

* @throws IllegalArgumentException if the FileDescriptor is invalid

*/

public void setDataSource(FileDescriptor fd)

throws IllegalArgumentException {

// intentionally less than LONG_MAX

setDataSource(fd, 0, 0x7ffffffffffffffL);

}

/**

* Sets the data source as a content Uri. Call this method before

* the rest of the methods in this class. This method may be time-consuming.

*

* @param context the Context to use when resolving the Uri

* @param uri the Content URI of the data you want to play

* @throws IllegalArgumentException if the Uri is invalid

* @throws SecurityException if the Uri cannot be used due to lack of

* permission.

*/

public void setDataSource(Context context, Uri uri)

throws IllegalArgumentException, SecurityException {

if (uri == null) {

throw new IllegalArgumentException();

}

String scheme = uri.getScheme();

if(scheme == null || scheme.equals(“file”)) {

setDataSource(uri.getPath());

return;

}

AssetFileDescriptor fd = null;

try {

ContentResolver resolver = context.getContentResolver();

try {

fd = resolver.openAssetFileDescriptor(uri, “r”);

} catch(FileNotFoundException e) {

throw new IllegalArgumentException();

}

if (fd == null) {

throw new IllegalArgumentException();

}

FileDescriptor descriptor = fd.getFileDescriptor();

if (!descriptor.valid()) {

throw new IllegalArgumentException();

}

// Note: using getDeclaredLength so that our behavior is the same

// as previous versions when the content provider is returning

// a full file.

if (fd.getDeclaredLength() < 0) {

setDataSource(descriptor);

} else {

setDataSource(descriptor, fd.getStartOffset(), fd.getDeclaredLength());

}

return;

} catch (SecurityException ex) {

} finally {

try {

if (fd != null) {

fd.close();

}

} catch(IOException ioEx) {

}

}

setDataSource(uri.toString());

}

/**

* Call this method after setDataSource(). This method retrieves the

* meta data value associated with the keyCode.

*

* The keyCode currently supported is listed below as METADATA_XXX

* constants. With any other value, it returns a null pointer.

*

* @param keyCode One of the constants listed below at the end of the class.

* @return The meta data value associate with the given keyCode on success;

* null on failure.

*/

public native String extractMetadata(int keyCode);

/**

* Call this method after setDataSource(). This method finds a

* representative frame if successful and returns it as a bitmap. This is

* useful for generating a thumbnail for an input media source.

*

* @return A Bitmap containing a representative video frame, which

*         can be null, if such a frame cannot be retrieved.

*/

public native Bitmap captureFrame();

/**

* Call this method after setDataSource(). This method finds the optional

* graphic or album art associated (embedded or external url linked) the

* related data source.

*

* @return null if no such graphic is found.

*/

public native byte[] extractAlbumArt();

/**

* Call it when one is done with the object. This method releases the memory

* allocated internally.

*/

public native void release();

private native void native_setup();

private static native void native_init();

private native final void native_finalize();

@Override

protected void finalize() throws Throwable {

try {

native_finalize();

} finally {

super.finalize();

}

}

public static final int MODE_GET_METADATA_ONLY  = 0×01;

public static final int MODE_CAPTURE_FRAME_ONLY = 0×02;

/*

* Do not change these values without updating their counterparts

* in include/media/mediametadataretriever.h!

*/

public static final int METADATA_KEY_CD_TRACK_NUMBER = 0;

public static final int METADATA_KEY_ALBUM           = 1;

public static final int METADATA_KEY_ARTIST          = 2;

public static final int METADATA_KEY_AUTHOR          = 3;

public static final int METADATA_KEY_COMPOSER        = 4;

public static final int METADATA_KEY_DATE            = 5;

public static final int METADATA_KEY_GENRE           = 6;

public static final int METADATA_KEY_TITLE           = 7;

public static final int METADATA_KEY_YEAR            = 8;

public static final int METADATA_KEY_DURATION        = 9;

public static final int METADATA_KEY_NUM_TRACKS      = 10;

public static final int METADATA_KEY_IS_DRM_CRIPPLED = 11;

public static final int METADATA_KEY_CODEC           = 12;

public static final int METADATA_KEY_RATING          = 13;

public static final int METADATA_KEY_COMMENT         = 14;

public static final int METADATA_KEY_COPYRIGHT       = 15;

public static final int METADATA_KEY_BIT_RATE        = 16;

public static final int METADATA_KEY_FRAME_RATE      = 17;

public static final int METADATA_KEY_VIDEO_FORMAT    = 18;

public static final int METADATA_KEY_VIDEO_HEIGHT    = 19;

public static final int METADATA_KEY_VIDEO_WIDTH     = 20;

public static final int METADATA_KEY_WRITER          = 21;

public static final int METADATA_KEY_MIMETYPE        = 22;

public static final int METADATA_KEY_DISCNUMBER      = 23;

public static final int METADATA_KEY_ALBUMARTIST     = 24;

// Add more here…

}