Android中如何获取视频文件的缩略图

核心提示：* @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 t

* @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