Android中的MediaMetadataRetriever类及其示例

MediaMetadataRetriever类提供了一个统一的接口，用于从输入媒体文件中检索帧和元数据。它位于android.media包下。例如：检索歌曲名称，艺术家名称，视频的宽度或高度，视频格式/ MIME类型，媒体的持续时间，媒体修改日期等。 MediaMetadataRetriever类提供的常量/键很多。这些常量用于检索媒体信息。尽管从它们的名称可以明显看出许多常量所做的工作，但这只是对MediaMetadataRetriever类中存在的每个常量的简短描述。

MediaMetadataRetriever类的重要常量

Constant Type	Constant Name	Description
int	METADATA_KEY_ALBUM	The metadata key to retrieve the information about the album title of the data source.
int	METADATA_KEY_ALBUMARTIST	The metadata key to retrieve the information about the performers or artist associated with the data source.
int	METADATA_KEY_ARTIST	The metadata key to retrieve the information about the artist of the data source.
int	METADATA_KEY_AUTHOR	The metadata key to retrieve the information about the author of the data source.
int	METADATA_KEY_CD_TRACK_NUMBER	The metadata key to retrieve the numeric string describing the order of the audio data source on its original recording.
int	METADATA_KEY_COMPILATION	The metadata key to retrieve the music album compilation status.
int	METADATA_KEY_COMPOSER	The metadata key to retrieve the information about the composer of the data source.
int	METADATA_KEY_DATE	The metadata key to retrieve the date when the data source was created or modified.
int	METADATA_KEY_DISC_NUMBER	The metadata key to retrieve the numeric string that describes which part of a set the audio data source comes from.
int	METADATA_KEY_DURATION	The metadata key to retrieve the playback duration of the data source.

Constant Type	Constant Name	Description
int	METADATA_KEY_GENRE	The metadata key to retrieve the content type or genre of the data source.
int	METADATA_KEY_MIMETYPE	The metadata key to retrieve the mime type of the data source.
int	METADATA_KEY_NUM_TRACKS	The metadata key to retrieve the number of tracks, such as audio, video, text, in the data source, such as a mp4 or 3gpp file.
int	METADATA_KEY_TITLE	The metadata key to retrieve the data source title.
int	METADATA_KEY_WRITER	The metadata key to retrieve the information of the writer (such as lyricist) of the data source.
int	METADATA_KEY_YEAR	The metadata key to retrieve the year when the data source was created or modified.
int	OPTION_CLOSEST	This option is used with getFrameAtTime(long, int) to retrieve a frame (not necessarily a keyframe) associated with a data source that is located closest to or at the given time.
int	OPTION_CLOSEST_SYNC	This option is used with getFrameAtTime(long, int) to retrieve a sync (or key) frame associated with a data source that is located closest to (in time) or at the given time.
int	OPTION_NEXT_SYNC	This option is used with getFrameAtTime(long, int) to retrieve a sync (or key) frame associated with a data source that is located right after or at the given time.
int	OPTION_PREVIOUS_SYNC	This option is used with getFrameAtTime(long, int) to retrieve a sync (or key) frame associated with a data source that is located right before or at the given time.

MediaMetadataRetriever类中可用的方法

Method Type	Methods
String	extractMetadata(int keyCode) Call this method after setDataSource().
byte[]	getEmbeddedPicture() Call this method after setDataSource().
Bitmap	getFrameAtTime(long timeUs, int option) Call this method after setDataSource().
Bitmap	getFrameAtTime(long timeUs) Call this method after setDataSource().
Bitmap	getFrameAtTime() Call this method after setDataSource().
void	release() Call it when one is done with the object. This method releases the memory allocated internally.
void	setDataSource(FileDescriptor fd, long offset, long length) Sets the data source (FileDescriptor) to use.
void	setDataSource(String path) Sets the data source (file pathname) to use.
void	setDataSource(FileDescriptor fd) Sets the data source (FileDescriptor) to use.
void	setDataSource(Context context, Uri uri) Sets the data source as a content Uri.
void	Close() Closes this resource, relinquishing any underlying resources.  This method is invoked automatically on objects managed by  the try-with-resources statement.

例子

1.获取mp3持续时间

这是Java的示例代码片段，用于获取mp3持续时间。  

Java

// load data file
// filePath is of type String which holds the path of file
MediaMetadataRetriever metaRetriever = new MediaMetadataRetriever();
metaRetriever.setDataSource(filePath);
  
// get mp3 info
String duration = metaRetriever.extractMetadata(MediaMetadataRetriever.METADATA_KEY_DURATION);
long dur = Long.parseLong(duration);
  
// convert duration to minute:seconds
String seconds = String.valueOf((dur % 60000) / 1000);
String minutes = String.valueOf(dur / 60000);
String out = minutes + ":" + seconds;
if (seconds.length() == 1) {
    txtTime.setText("0" + minutes + ":0" + seconds);
}
else {
    txtTime.setText("0" + minutes + ":" + seconds);
}
  
// close object
metaRetriever.release();

2.检测视频的方向

以下是一个示例视频

这是Java的示例代码片段，用于检测视频的方向

Java

MediaMetadataRetriever m = new MediaMetadataRetriever();
  
// load data file
m.setDataSource(path);
  
// getting the bitmap of a frame from video
Bitmap thumbnail = m.getFrameAtTime();
  
if (Build.VERSION.SDK_INT >= 17) {
    String s = m.extractMetadata(MediaMetadataRetriever.METADATA_KEY_VIDEO_ROTATION);
}
  
// Another way of determining whether the video is Landscape or portrait
MediaMetadataRetriever retriever = new MediaMetadataRetriever();
retriever.setDataSource(inputPath);
video_width = Integer.valueOf(retriever.extractMetadata(MediaMetadataRetriever.METADATA_KEY_VIDEO_WIDTH));
video_height = Integer.valueOf(retriever.extractMetadata(MediaMetadataRetriever.METADATA_KEY_VIDEO_HEIGHT));
  
// close object
retriever.release();
  
// If the width is bigger than the height then it means that
// the video was taken in landscape mode and vice versa.
if ((video_width > video_height)) {
    // landscape
}
else {
    // portrait
}

3.在音乐应用中设置专辑封面和专辑标题

以下是示例图片

这是Java的示例代码段，用于在Music App中设置专辑封面和专辑标题。

Java

MediaMetadataRetriever retriever = new MediaMetadataRetriever();
retriever.setDataSource(filePath);
  
// getting the embedded picture from media
byte[] art = retriever.getEmbeddedPicture();
  
if (art != null) {
    // Convert the byte array to a bitmap
    imgAlbum.setImageBitmap(BitmapFactory.decodeByteArray(art, 0, art.length));
}
else {
    imgAlbum.setImageResource(R.drawable.no_image);
}
// close object
retriever.release();

4.制作像TikTok这样的CropVideo活动

以下是一个示例视频

这是Java用于制作CropVideo活动(如TikTok)的示例代码段。

Java

try {
    MediaMetadataRetriever mediaMetadataRetriever = new MediaMetadataRetriever();
    mediaMetadataRetriever.setDataSource(context, videoUri);
  
    // Retrieve media data use microsecond
    long interval = (endPosition - startPosition) / (totalThumbsCount - 1);
    for (long i = 0; i < totalThumbsCount; ++i) {
        long frameTime = startPosition + interval * i;
        Bitmap bitmap = mediaMetadataRetriever.getFrameAtTime(frameTime * 1000, MediaMetadataRetriever.OPTION_CLOSEST_SYNC);
        if (bitmap == null)
            continue;
        try {
            bitmap = Bitmap.createScaledBitmap(bitmap, THUMB_WIDTH, THUMB_HEIGHT, false);
        }
        catch (final Throwable t) {
            t.printStackTrace();
        }
        // add bitmaps to the recyclerview here…
    }
    mediaMetadataRetriever.release();
}
catch (final Throwable e) {
    Thread.getDefaultUncaughtExceptionHandler().uncaughtException(Thread.currentThread(), e);
}

Note:

1. Always check for illegal filePath.
2. Handle the null bitmap condition. There may be cases when the media doesn’t return a valid bitmap.
3. The frame index must be that of a valid frame. The total number of frames available for retrieval can be queried via the METADATA_KEY_VIDEO_FRAME_COUNT key.
4. When retrieving the frame at the given time position, there is no guarantee that the data source has a frame located at the position. When this happens, a frame nearby will be returned. If time is negative, time position and option will be ignored, and any frame that the implementation considers as representative may be returned.
5. setDataSource(), Call this method before the rest of the methods in this class. This method may be time-consuming.

参考链接： https : //developer.android.com/reference/android/media/MediaMetadataRetriever

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