Commit | Line | Data |
---|---|---|
5377d91f MH |
1 | .. -*- coding: utf-8; mode: rst -*- |
2 | ||
3 | .. _streaming-par: | |
4 | ||
5 | ******************** | |
6 | Streaming Parameters | |
7 | ******************** | |
8 | ||
9 | Streaming parameters are intended to optimize the video capture process | |
10 | as well as I/O. Presently applications can request a high quality | |
af4a4d0d | 11 | capture mode with the :ref:`VIDIOC_S_PARM <VIDIOC_G_PARM>` ioctl. |
5377d91f MH |
12 | |
13 | The current video standard determines a nominal number of frames per | |
14 | second. If less than this number of frames is to be captured or output, | |
15 | applications can request frame skipping or duplicating on the driver | |
16 | side. This is especially useful when using the | |
17 | :ref:`read() <func-read>` or :ref:`write() <func-write>`, which are | |
18 | not augmented by timestamps or sequence counters, and to avoid | |
19 | unnecessary data copying. | |
20 | ||
21 | Finally these ioctls can be used to determine the number of buffers used | |
22 | internally by a driver in read/write mode. For implications see the | |
23 | section discussing the :ref:`read() <func-read>` function. | |
24 | ||
25 | To get and set the streaming parameters applications call the | |
4e03cb76 | 26 | :ref:`VIDIOC_G_PARM <VIDIOC_G_PARM>` and |
af4a4d0d | 27 | :ref:`VIDIOC_S_PARM <VIDIOC_G_PARM>` ioctl, respectively. They take |
5377d91f MH |
28 | a pointer to a struct :ref:`v4l2_streamparm <v4l2-streamparm>`, which |
29 | contains a union holding separate parameters for input and output | |
30 | devices. | |
31 | ||
32 | These ioctls are optional, drivers need not implement them. If so, they | |
33 | return the EINVAL error code. | |
34 | ||
35 | ||
36 | .. ------------------------------------------------------------------------------ | |
37 | .. This file was automatically converted from DocBook-XML with the dbxml | |
38 | .. library (https://github.com/return42/sphkerneldoc). The origin XML comes | |
39 | .. from the linux kernel, refer to: | |
40 | .. | |
41 | .. * https://github.com/torvalds/linux/tree/master/Documentation/DocBook | |
42 | .. ------------------------------------------------------------------------------ |