Merge pull request #99 from taorye/dev

doc: need guvcview to select mjpeg channel or direct on v4l2

Author: Neutree

docs/doc/en/video/uvc_streaming.md

@@ -21,6 +21,14 @@ Here, two methods are provided to display custom content:
 
 **First, you need to enable the `UVC` function in the `USB settings` section of the `Settings` app.**
 
+After connecting the USB cable:
+
+- Windows users can go to Settings → Bluetooth & devices → Cameras, and see the UVC Camera device. Clicking on it will preview a static image of a small cat.
+
+- Linux users need to download the `guvcview` software, select the resolution of 320x240 and the format as MJPG. You will see two cats with some garbled characters in between (this happens because the actual resolution of the cat image is 224x224, and the software automatically tries to fill the remaining space with another thing). Simply use the correct resolution normally.
+
+Note: The version of guvcview used in Ubuntu 22 and earlier systems is `2.0.7`, which is known that the colors are displayed incorrectly, with a strong green tint. To fix it, please upgrade to a higher version. The version currently in use by the author is `2.2.1`. Ubuntu/Debian users can try to find a relevant PPA (Personal Package Archive) to install a newer version of guvcview.
+
 **Note:**  
 Once the `UVC` function is enabled, due to Linux's implementation of the `UVC Gadget`, a user program is still required to handle `UVC` device events.  
 Otherwise, the entire `USB` functionality will pause and wait, affecting other simultaneously enabled `Gadget` features like `Rndis` and `NCM`, which may cause network disconnection.  

docs/doc/zh/video/uvc_streaming.md

@@ -18,6 +18,13 @@ update:
 
 首先需要在 `Settings` APP 的 `USB settings` 栏内启用 `UVC` 功能。
 
+连接 usb 线缆后：
+
+- Windows 用户可在`设置-蓝牙和设备-摄像头`内，看到 UVC Camera设备，点进去即可预览到一张静态小猫图。
+- Linux 用户，需要下载软件 `guvcview`，并选择分辨率为 320x240，格式为 MJPG，会看到两个小猫中间隔着乱码（原因是该小猫图片实际分辨率为 224x224，该软件自动拼了下一张过来，实际使用时使用正常的分辨率即可）
+
+注意： 当前 Ubuntu 22 及更早系统版本使用的 guvcview 软件版本为 2.0.7，已知现象是显示色彩不对，严重偏绿。请换用更高版本即可正常显示，作者当前使用的版本号是 2.2.1。Ubuntu/Debian 用户可以尝试寻找相关的 PPA（个人包档案）来安装较新的 guvcview 版本。
+
 注意： `UVC` 功能启用后，因为 Linux 的 `UVC Gadget` 实现，仍需一个用户程序处理 `UVC` 设备的事件，
 否则整个 `USB` 功能会暂停等待，影响同时启用的其它 `Gadget` 功能，包括 `Rndis` 和 `NCM`，导致断网。
 故对于其它 `USB` 功能有需求的用户，在基于 `MaixPy` 开发 UVC 显示功能时建议采用 `UvcStreamer` 的实现。