android YV12 地址偏移 與 line_stride 對齊

1.buffer地址偏移
以分辨率 1280*720 格式爲YV12 爲例，Y起始地址爲0x100000000 ,且是連續

y_addr   = 0x100000000;
cb_addr =  y_addr  + 1280×720；
cr_addr =  cb_addr + 1280*720/4;

2.line stride計算
需要考慮到不同硬件使用相同的地址，如camera 寫buffer display去顯示。而兩個硬件的line stride 要求不同，則需要計算一個line stride 來滿足他們。下面是android 官網給的計算方式.
PS: line stride 可以理解爲硬件寫一行數據的大小，
如 1028 ×720 對齊後 1280×720 .則硬件每次寫一行數據爲1280，一共寫720行，這樣就把對應的Y數據寫完

Android YUV format.

This format is exposed to software decoders and applications.

YV12 is a 4:2:0 YCrCb planar format comprised of a WxH Y plane followed by (W/2) x (H/2) Cr and Cb planes.

This format assumes

an even width
an even height
a horizontal stride multiple of 16 pixels
a vertical stride equal to the height
 y_size = stride * height
 c_stride = ALIGN(stride/2, 16)
 c_size = c_stride * height/2
 size = y_size + c_size * 2
 cr_offset = y_size
 cb_offset = y_size + c_size

NV21 的line stride

cb_stride = y_stride;
cr_stride = 0;