android当中获取视频音频的时长，三种。
1：获取视频URI后获取cursor
cursor.getLong(cursor.getColumnIndexOrThrow(MediaStore.Video.Media.DURATION));
2：根据MediaPlayer获取：
MediaPlayer mediaPlayer = new MediaPlayer();
mediaPlayer.setDataSource(url);
mediaPlayer.prepare();
mediaPlayer.getDuration();
3:采用MediaMetadataRetriever的方式：
public static String getRingDuring(String mUri){
String duration=null;
android.media.MediaMetadataRetriever mmr = new android.media.MediaMetadataRetriever();
try { if (mUri != null) { HashMap<String, String> headers=null;
if (headers == null) { headers = new HashMap<String, String>();
headers.put("User-Agent", "Mozilla/5.0 (Linux; U; Android 4.4.2; zh-CN; MW-KW-001 Build/JRO03C) AppleWebKit/533.1 (KHTML, like Gecko) Version/4.0 UCBrowser/1.0.0.001 U4/0.8.0 Mobile Safari/533.1"); }
mmr.setDataSource(mUri, headers); }
duration = mmr.extractMetadata(android.media.MediaMetadataRetriever.METADATA_KEY_DURATION); }
catch (Exception ex) { }
finally { mmr.release(); }
LogUtil.e("ryan","duration "+duration); return duration; }