video的帧可区分为隔行和逐行： 逐行顺序的传输一帧所有的行，而隔行则把一帧划分成两个fields，分别保存帧的奇数行和偶数行，被称作奇场和偶场. 阴极射线电视机需要交替的显示两场来组成一个完整的帧，交替的时延需要我们交替的传输奇场和偶
video的帧可区分为隔行和逐行： 逐行顺序的传输一帧所有的行，而隔行则把一帧划分成两个fields，分别保存帧的奇数行和偶数行，被称作奇场和偶场. 阴极射线电视机需要交替的显示两场来组成一个完整的帧，交替的时延需要我们交替的传输奇场和偶场。这个奇怪技术的引入是因为：在刷新率接近电影时，图片会消退的过快。使用奇偶场可以避免使用双倍的buffer以及额外的带宽需求。
首先要明确模拟camera（数字摄像头不在这个讨论之列。）并不是在同一时间曝光一帧，camera通过场来传输这些帧的，这些场是在不同瞬间拍摄的。屏幕上的一个运动对象因此会在两个field之间产生动画效果。这种情况下需要识别哪一帧更老一点，也称作“瞬间序”。
当驱动通过场提供或者接收images，应用应该知道如何通过这些场组合成帧，通过划分为top bottom 场，顶场的第一行是帧的第一行，底场的第一行是帧的第二行。
然而因为field是一个跟着一个拍的，争论帧是由top还是bottom开始的是没意义的，任何两个相邻的top bottom场, 或者 bottom top场都可以组成一个有效的帧。
与直觉相反，top 场不一定排在bottom前面, top和bottom到底谁先谁后，是由video标准决定的。因此要区分瞬间序和空间序，下面的图会给出清晰的解释。
所有的video capture和out devices必须汇报当前的field顺序。 一些驱动可能允许选择不同的序，终端应用可以在调用VIDIOC_S_FMT前初始化struct v4l2_pix_format的 field成员。否则可以使用V4L2_FIELD_ANY
下面列出了可能的field类型
| V4L2_FIELD_ANY | 0 |
Application 可以请求使用这个参数，如果V4L2_FIELD_NONE, V4L2_FIELD_TOP, V4L2_FIELD_BOTTOM Ｖ4L2_FIELD_INTERLACE 中任何一个格式都支持．驱动选择使用哪一个格式依赖于硬件能力，以及请求的image尺寸，驱动选择一个然后返回这个格式。struct_buffer的field成员不可以为V4L2_FIELD_ANY.
|
| V4L2_FIELD_NONE | 1 |
Images是逐行格式，当驱动无法区分V4L2_FIELD_TOP和V4L2_FIELD_BOTTOM，可以使用这种field类型
|
| V4L2_FIELD_TOP | 2 |
Images仅仅包含top field
|
| V4L2_FIELD_BOTTOM | 3 |
Images仅仅包含bottom field，应用可能希望防止设备捕获interlaced的图片，因为这种图片会在运动物体周围产生毛状特效
|
| V4L2_FIELD_INTERLACED | 4 |
Images包含top和bottom field, 隔行交替，场序依赖于当前video的标准。NTSC首先传输bottom field, PAL则先传输top field。
|
| V4L2_FIELD_SEQ_TB | 5 |
Images包含top和bottom field, top field的行首先存放在memory中，然后紧跟着bottom field的行。 Fields一直以瞬间序存储，较老的放在内存前面。Images的尺寸和帧相关，而不是field
|
| V4L2_FIELD_SEQ_BT | 6 |
Images包含top和bottom field, bottom field的行首先存放在memory中，然后紧跟着top field的行。 Fields一直以瞬间序存储，较老的放在内存前面。Images的尺寸和帧相关，而不是field
|
| V4L2_FIELD_ALTERATE | 7 |
一个帧的两个field分别放在不同的buffer, 按照瞬间序，也就是说老的一个是第一个。driver或者应用指明field的奇偶性（奇偶性：当前的field是top 还是bottom field）. 任何两个连续的field构成一个frame，是否两个field是连续的，不需要drop掉他们，可以通过v4l2_buffer中的sequence 成员判定。Images的尺寸和frame相关而不是fields相关
|
| V4L2_FIELD_INTERLACED_TB | 8 |
Images 包含top和bottom field, 每行交替， top field在前面。top field首先传送
|
| V4L2_FIELD_INTERLACED_BT | 9 | Images 包含top和bottom field, 每行交替， bottom field在前面。bottom field首先传送 |
Field Order, Top Field First Transmitted
Field Order, Bottom Field First Transmitted
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