android camera yuv帧水平翻转

Camera预览时需要对yuv帧做水平翻转处理，直接在onPreviewFrame(byte[] data, Camera camera)里调用Mirror函数，处理完后的图片和预览效果成水平翻转关系。

nv21的镜像算法：

    private void Mirror(byte[] src, int w, int h) { //src是原始yuv数组
        int i;
        int index;
        byte temp;
        int a, b;
        //mirror y
        for (i = 0; i < h; i++) {
            a = i * w;
            b = (i + 1) * w - 1;
            while (a < b) {
                temp = src[a];
                src[a] = src[b];
                src[b] = temp;
                a++;
                b--;
            }
        }

        // mirror u and v
        index = w * h;
        for (i = 0; i < h / 2; i++) {
            a = i * w;
            b = (i + 1) * w - 2;
            while (a < b) {
                temp = src[a + index];
                src[a + index] = src[b + index];
                src[b + index] = temp;

                temp = src[a + index + 1];
                src[a + index + 1] = src[b + index + 1];
                src[b + index + 1] = temp;
                a+=2;
                b-=2;
            }
        }
    }

i420的镜像算法：

private void Mirror(byte[] src, int w, int h) { //src是原始yuv数组
        int i;
        int index;
        byte temp;
        int a, b;
        //mirror y
        for (i = 0; i < h; i++) {
            a = i * w;
            b = (i + 1) * w - 1;
            while (a < b) {
                temp = src[a];
                src[a] = src[b];
                src[b] = temp;
                a++;
                b--;
            }
        }
        //mirror u
        index = w * h;//U起始位置
        for (i = 0; i < h / 2; i++) {
            a = i * w / 2;
            b = (i + 1) * w / 2 - 1;
            while (a < b) {
                temp = src[a + index];
                src[a + index] = src[b + index];
                src[b + index] = temp;
                a++;
                b--;
            }
        }
        //mirror v
        index = w * h / 4 * 5;//V起始位置
        for (i = 0; i < h / 2; i++) {
            a = i * w / 2;
            b = (i + 1) * w / 2 - 1;
            while (a < b) {
                temp = src[a + index];
                src[a + index] = src[b + index];
                src[b + index] = temp;
                a++;
                b--;
            }
        }

I420，YV12，NV12，NV21均属于YUV420，以下为四种格式的排列顺序：

I420:  YYYYYYYY UUVV     =>YUV420P
YV12: YYYYYYYY VVUU     =>YUV420P
NV12: YYYYYYYY UVUV     =>YUV420SP
NV21: YYYYYYYY VUVU     =>YUV420SP