V4L2中兩個關於映像佔用空間大小的結構體項的理解

1.struct v4l2_pix_format 中的sizeimage
其說明為：   
   Size in bytes of the buffer to hold a complete image, set by the driver.
Usually this is bytesperline times height. When the image consists of variable
length compressed data this is the maximum number of bytes required to hold
an image.
  表示的是當前採集參數下，映像資料需要的最大位元組數。

2.struct v4l2_buffer 中的bytesused
其說明為：
   The number of bytes occupied by the data in the buffer.It depends on the
negotiated data format and may change with each buffer for compressed variable
size data like JPEG images. Drivers must set this field when type refers to an
input stream, applications when an output stream.
  表示的是當前，映像資料實際佔用的位元組數。