src/main/java/org/jcodec/codecs/h264/decode/BlockInterpolator.java
void getLuma31(byte[] pels, int picW, byte[] blk, int blkOff, int blkStride, int x, int y, int blkW,
            int blkH) {
        getLuma20(pels, picW, blk, blkOff, blkStride, x, y, blkW, blkH);
        getLuma02(pels, picW, tmp3, 0, blkW, x + 1, y, blkW, blkH);

        merge(blk, tmp3, blkOff, blkStride, blkW, blkH);
    }
void getLuma31(byte[] pels, int picW, byte[] blk, int blkOff, int blkStride, int x, int y, int blkW,
            int blkH) {
        getLuma20(pels, picW, blk, blkOff, blkStride, x, y, blkW, blkH);
        getLuma02(pels, picW, tmp3, 0, blkW, x + 1, y, blkW, blkH);

        merge(blk, tmp3, blkOff, blkStride, blkW, blkH);
    }
Qpel horizontal, Qpel vertical (3, 1)