Android平台下怎么把JPEG格式的图片转化成NV21

如题，Android平台下怎么把JPEG格式的图片转化成NV21？

请大神指点一下。

问题解决了！
感谢各位的思路，https://github.com/gqjjqg/android-extend

参考：https://stackoverflow.com/questions/5960247/convert-bitmap-array-to-yuv-ycbcr-nv21
至于jpeg->bitmap，这个代码很好找吧。

先转为 base 64

按照下面的方式应该可以得到解决：

 void yourFunction(){

    // mBitmap is your bitmap

    int mWidth = mBitmap.getWidth();
    int mHeight = mBitmap.getHeight();

    int[] mIntArray = new int[mWidth * mHeight];

    // Copy pixel data from the Bitmap into the 'intArray' array
    mBitmap.getPixels(mIntArray, 0, mWidth, 0, 0, mWidth, mHeight);

    // Call to encoding function : convert intArray to Yuv Binary data
    encodeYUV420SP(data, intArray, mWidth, mHeight);

}

static public void encodeYUV420SP(byte[] yuv420sp, int[] rgba,
        int width, int height) {
    final int frameSize = width * height;

    int[] U, V;
    U = new int[frameSize];
    V = new int[frameSize];

    final int uvwidth = width / 2;

    int r, g, b, y, u, v;
    for (int j = 0; j < height; j++) {
        int index = width * j;
        for (int i = 0; i < width; i++) {

            r = Color.red(rgba[index]);
            g = Color.green(rgba[index]);
            b = Color.blue(rgba[index]);

            // rgb to yuv
            y = (66 * r + 129 * g + 25 * b + 128) >> 8 + 16;
            u = (-38 * r - 74 * g + 112 * b + 128) >> 8 + 128;
            v = (112 * r - 94 * g - 18 * b + 128) >> 8 + 128;

            // clip y
            yuv420sp[index] = (byte) ((y < 0) ? 0 : ((y > 255) ? 255 : y));
            U[index] = u;
            V[index++] = v;
        }
    }