kickxxx的专栏

Your editor has recently had the opportunity to write a Linux driver for acamera device - the camera which will be packaged with the One Laptop PerChild system, in particular. This driver works with t

JPEG是Joint Photographic Experts Group 的缩写，正是这个专家组制定了JPEG标准以及其他静态图片编解码标准。Joint（联合）是指ISO TC97 WG8（计算机与信息处理技术委员会 第8工作组）和CCITT SGVIII两个工作组的联合. 这个专家组在1992年颁布了第一个JPEG标准, ITU在1992年命名为ITU-T Recommendation T.8

代码如下，注释可参看原文http://users.suse.com/~mana/alsa090_howto.html#include int main(){ int ret; snd_pcm_t *pcm_handle; snd_pcm_stream_t stream = SND_PCM_STREAM_PLAYBACK; snd_pcm_hw_params_t *hwpa

原文地址 http://alsa.opensrc.org/Plugin_DocumentationOfficial documentationALSA plugins的官方文档地址是http://www.alsa-project.org/alsa-doc/alsa-lib/pcm_plugins.html此外还可以在下面地址发现有用的信息：http://www.alsa-p

static LIST_HEAD(hosts)所有的host都在hosts指向的链表上static LIST_HEAD(devices);所有soc camera device都挂在devices指向的链表上。系统内可能有多个soc_camera_host，每个soc_camera_host可以对应1 ~ n个soc_camera_device。每个soc_camera_d

采样(sample)：PCM audio不论是输入还是输出，都包含采样，采样达标声音的一个声道在某个特定时间点的振幅。 很多这样的采样组成了声音。样本是记录音频数据的最基本单位。对于CD audio，每秒有44100个采样。采样的尺寸从8bit 到64bit精度。采样的格式也各式各样： 大端整形，小端整形或者浮点数。采样尺寸决定动态声响范围。动态声响范围是指最静和最大声之差通道

soc_camera.c1455 static struct platform_driver __refdata soc_camera_pdrv = {1456     .remove  = __devexit_p(soc_camera_pdrv_remove),1457     .driver  = {1458         .name   = "soc-camera-pdr

图1 soc camera 子系统 系统架构图Soc camera sub-system对应着drivers/media/video/下的soc_camera.c soc_camera_platform.cSoc camera host 是host端实现，是由平台厂商实现的，向上实现soc_camera_host_ops接口，向下操作Camera host硬件以及通过平台特定的

soc-camera的作者之所以引入这个子系统，我想一个主要目的就是把camera驱动划分为camera host端，camera device端，这样同一个camera sensor驱动就可以方便的移植到多个camera host下，而无须做较多的改动。本译文取自kernel文档：Documentation/video4linux/soc-camera.txt术语

YUV是图像色彩空间的一种色彩模型，该模型将亮度和色度分开，常用的三种色彩模型为RGB CMYK和YUV。YCbCr是ITU-R BT601的一部分，是YUV经过缩放和偏移处理后的结果。其中Y与YUV中的Y含义一致，Cb Cr同样都指色彩。二者到RGB空间的转换公式也不一样Y’ = 0.257*R' + 0.504*G' + 0.098*B' + 16Cb' =

应用层通过设备节点/dev/videoX打开video4linux devices。/dev/videoX是一个字符设备，主设备号81，次设备号： (0～63)分配给capture设备，64~127分配给radio设备，223~255分配给VBI设备，128~191分配给其他类型的。如果驱动要注册一个video4linux设备，那么需要调用video_register_device函数。

在做video AD视频转换时，碰到DVD输出的CVBS信号转换后，输出的原始图像宽度并不能充满整个屏幕720pixels，而是左右各有大概8pixels也就是只有704个pixels。这就涉及到DVD官方规定的合法resolutions，在这里也许不该叫resolutions，而是应该称之为"frame size"720x576 (480 NTSC)，称为D1标准又称为"

今天整理tw9912驱动，发现FIMC 在capture时，对S_FMT和G_FMT ioctl调用值得商榷，记录下来。当capture APP调用S_FMT时，会调用到FIMC capture驱动的fimc_s_fmt_vid_capture函数 814 int fimc_s_fmt_vid_capture(struct file *file, void *fh, struct v4

This is the second article in the LWN series on writing drivers for theVideo4Linux2 kernel interface; those who have not yet seenthe introductory article maywish to start there. This installment wil

This is the fourth article in the irregular LWN series on writing videodrivers for Linux. Those who have not yet readthe introductory article maywant to start there. This week's episode describes ho

This article is a continuation of the irregular LWN series on writing videodrivers for Linux. Theintroductory article describes theseries and contains pointers to the previous articles. Inthe last

The previous installment inthis series discussed how to transfer video frames with theread()and write() system calls. Such an implementation can get thebasic job done, but it is not normally the pre

Anybody who has spent any amount of time working through the Video4Linux2 APIspecification will have certainly noted that V4L2 makes heavy use oftheioctl() interface. Perhaps more than just about

在网上找了一个测试程序， 看了看，是根据capture.c修改的。测试步骤如下1. gcc -o capture_image capture_image.c2. ctrl+alt+f1 切换到ubuntu的控制台，切换到控制台模式是因为在图形模式下看不到测试图形，这可能和framebuffer的设置有关3. sudo modprobe vivi4. sudo ./capture_i

This is the fifth article in the irregular LWN series on writing videodrivers for Linux. Those who have not yet readthe introductory article maywant to start there.Before any application can work

This series of articles onvideo drivers has been through several installments, but we have yet to transfer a single frame of video data. Atthis point, though, we have covered enough of the format nego

三者都是V4L2定义的接口，英文原文参见 http://v4l2spec.bytesex.org/spec-single/v4l2.html#OVERLAYVideo Overlay: Video overlay devices have the ability to genlock (TV-)video into the (VGA-)video signal of a graph

视频应用可以通过两种方式从V4L2驱动申请buffer1. USERPTR， 顾名思义是用户空间指针的意思，应用层负责分配需要的内存空间，然后以指针的形式传递给V4L2驱动层，V4L2驱动会把capture的内容保存到指针所指的空间一般来说，应用层需要确保这个内存空间物理上是连续的（IPU处理单元的需求），在android系统可以通过PMEM驱动来分配大块的连续物理内存。应用层在不需要的时