How to get YUV420 data?

[sunnymanlxh]

When I use the lib decode h264 data, use vlc --vout cedarfb can display right picture, but I save the YUV data to file and use other YUV tools to see, can't see the right picture. The picture size is 1280*720, but the size_y[0] is 942080 and size_u[0] is 491520, why?

thank you.