H264解析Demo11帧内预测编码_2_获得参考的像素值

Posted 2021-05-17 叮咚咕噜

基础知识请参考：
十五、帧内编码：3、获取预测数据

知识储备

保存邻块像素值到数组中，数组的存放顺序如下图：（绿色为当前待解析的4 * 4宏块）

定义

//<预测编码><6>表示44=16个子宏块 * （44=16）每个子宏块中的4*4个像素 （先是列坐标）

UINT8 m_reconstructed_block[4][4][4][4];

代码实现

//<预测编码><5>获得参考像素：neighbors相邻宏块，当前宏块index,refPixBuf参考像素的值
int CMacroblock::get_reference_pixels(NeighborBlocks neighbors, UINT8 blkIdx, UINT8 *refPixBuf)
{
	bool available_left = neighbors.flags & 1, available_top = neighbors.flags & 2, available_top_right = neighbors.flags & 4, available_top_left = neighbors.flags & 8;
	UINT8 blk_row = -1, blk_column = -1;
	CMacroblock *ref_mb = NULL;

	block_index_to_position(blkIdx, blk_row, blk_column);	//<预测编码><6>根据index获得在当前宏块中的位置

	if (available_left)
	{
		ref_mb = m_slice->Get_macroblock_at_index(neighbors.left.target_mb_idx);
		refPixBuf[0] = ref_mb->m_reconstructed_block[neighbors.left.block_column][neighbors.left.block_row][3][3];
		refPixBuf[1] = ref_mb->m_reconstructed_block[neighbors.left.block_column][neighbors.left.block_row][2][3];
		refPixBuf[2] = ref_mb->m_reconstructed_block[neighbors.left.block_column][neighbors.left.block_row][1][3];
		refPixBuf[3] = ref_mb->m_reconstructed_block[neighbors.left.block_column][neighbors.left.block_row][0][3];
	} 
	else
	{
		refPixBuf[0] = refPixBuf[1] = refPixBuf[2] = refPixBuf[3] = 128;
	}

	if (available_top_left)
	{
		ref_mb = m_slice->Get_macroblock_at_index(neighbors.top_left.target_mb_idx);
		refPixBuf[4] = ref_mb->m_reconstructed_block[neighbors.top_left.block_column][neighbors.top_left.block_row][3][3];
	} 
	else
	{
		refPixBuf[4] = 128;
	}

	if (available_top)
	{
		ref_mb = m_slice->Get_macroblock_at_index(neighbors.top.target_mb_idx);
		refPixBuf[5] = ref_mb->m_reconstructed_block[neighbors.top.block_column][neighbors.top.block_row][3][0];
		refPixBuf[6] = ref_mb->m_reconstructed_block[neighbors.top.block_column][neighbors.top.block_row][3][1];
		refPixBuf[7] = ref_mb->m_reconstructed_block[neighbors.top.block_column][neighbors.top.block_row][3][2];
		refPixBuf[8] = ref_mb->m_reconstructed_block[neighbors.top.block_column][neighbors.top.block_row][3][3];
	} 
	else
	{
		refPixBuf[5] = refPixBuf[6] = refPixBuf[7] = refPixBuf[8] = 128;
	}

	if (available_top_right)
	{
		ref_mb = m_slice->Get_macroblock_at_index(neighbors.top_right.target_mb_idx);
		refPixBuf[9] = ref_mb->m_reconstructed_block[neighbors.top_right.block_column][neighbors.top_right.block_row][3][0];
		refPixBuf[10] = ref_mb->m_reconstructed_block[neighbors.top_right.block_column][neighbors.top_right.block_row][3][1];
		refPixBuf[11] = ref_mb->m_reconstructed_block[neighbors.top_right.block_column][neighbors.top_right.block_row][3][2];
		refPixBuf[12] = ref_mb->m_reconstructed_block[neighbors.top_right.block_column][neighbors.top_right.block_row][3][3];
	} 
	else
	{
		refPixBuf[9] = refPixBuf[10] = refPixBuf[11] = refPixBuf[12] = refPixBuf[8];		//<预测编码><6>如果右上是不可获取的，则将其像素值写为 refPixBuf[8]，标准文档定义
	}

	return kPARSING_ERROR_NO_ERROR;
}