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| USB摄像头有一个全平台统一的BUG，就是2个或者多个USB摄像头插在同一个USB总线上，即使用USB-HUB扩展的口，会出现第二个摄像头无法打开的情况。目前一个项目需要在V3S上启用2个USB摄像头，就遇到了麻烦，同时也解决了上一篇文章只有`YUV`格式才能输出 `mjpg-streamer` 的BUG。 | ||
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| ### 填坑 | ||
| 先把上一篇文章的坑先解决了，由于之前很少搞`buildroot`相关的东西，所以开始的时候就在谷歌上查阅了很多资料，正是这些资料让我进入了这么一个大坑（不过也学到了很多）。坑：`mjpg-streamer` 需要单独交叉编译然后拷贝进嵌入式板子是唯一的解决办法。 | ||
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| 其实使用 `buildroot` 根本不需要再单独下载源代码/配置/编译等，直接 `make menuconfig` 在里面启用 `mjpg-streamer` 和 `libjpeg` 就可以了（Target packages > Networking applications）~~~我真是个大冤种。 | ||
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| 体现在 `.config` 文件中就是修改这么几句代码： | ||
| ``` | ||
| BR2_PACKAGE_MJPG_STREAMER=y | ||
| BR2_PACKAGE_JPEG=y | ||
| BR2_PACKAGE_LIBJPEG=y | ||
| BR2_PACKAGE_PROVIDES_JPEG="libjpeg" | ||
| ``` | ||
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| ### 启用多摄像头 | ||
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| 启用第二个摄像头报错如下： | ||
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| ``` | ||
| VIDIOC_STREAMON: No space left on device | ||
| ``` | ||
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| 网上有这样的解决方式： | ||
| ``` | ||
| # 减低帧率和分辨率 | ||
| ``` | ||
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| 还有这样的： | ||
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| ``` | ||
| sudo rmmod uvcvideo | ||
| sudo modprobe uvcvideo quirks=128 | ||
| ``` | ||
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| 对于我来说，下面这个实测有效： | ||
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| ``` | ||
| # 修改内核源码，在buildroot的目录下面就是这个路径文件 | ||
| output\build\linux-zero-4.13.y\drivers\media\usb\uvc\uvc_video.c | ||
| # 找到这个文件中的函数 uvc_fixup_video_ctrl | ||
| # 在这个函数的最后添加一行代码 | ||
| if(format->flags & UVC_FMT_FLAG_COMPRESSED){ctrl->dwMaxPayloadTransferSize = 0x400;} | ||
| ``` | ||
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| 为了更加清晰，下面是修改后的 `uvc_fixup_video_ctrl` 代码 | ||
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| ``` | ||
| static void uvc_fixup_video_ctrl(struct uvc_streaming *stream, | ||
| struct uvc_streaming_control *ctrl) | ||
| { | ||
| struct uvc_format *format = NULL; | ||
| struct uvc_frame *frame = NULL; | ||
| unsigned int i; | ||
| for (i = 0; i < stream->nformats; ++i) { | ||
| if (stream->format[i].index == ctrl->bFormatIndex) { | ||
| format = &stream->format[i]; | ||
| break; | ||
| } | ||
| } | ||
| if (format == NULL) | ||
| return; | ||
| for (i = 0; i < format->nframes; ++i) { | ||
| if (format->frame[i].bFrameIndex == ctrl->bFrameIndex) { | ||
| frame = &format->frame[i]; | ||
| break; | ||
| } | ||
| } | ||
| if (frame == NULL) | ||
| return; | ||
| if (!(format->flags & UVC_FMT_FLAG_COMPRESSED) || | ||
| (ctrl->dwMaxVideoFrameSize == 0 && | ||
| stream->dev->uvc_version < 0x0110)) | ||
| ctrl->dwMaxVideoFrameSize = | ||
| frame->dwMaxVideoFrameBufferSize; | ||
| /* The "TOSHIBA Web Camera - 5M" Chicony device (04f2:b50b) seems to | ||
| * compute the bandwidth on 16 bits and erroneously sign-extend it to | ||
| * 32 bits, resulting in a huge bandwidth value. Detect and fix that | ||
| * condition by setting the 16 MSBs to 0 when they're all equal to 1. | ||
| */ | ||
| if ((ctrl->dwMaxPayloadTransferSize & 0xffff0000) == 0xffff0000) | ||
| ctrl->dwMaxPayloadTransferSize &= ~0xffff0000; | ||
| if (!(format->flags & UVC_FMT_FLAG_COMPRESSED) && | ||
| stream->dev->quirks & UVC_QUIRK_FIX_BANDWIDTH && | ||
| stream->intf->num_altsetting > 1) { | ||
| u32 interval; | ||
| u32 bandwidth; | ||
| interval = (ctrl->dwFrameInterval > 100000) | ||
| ? ctrl->dwFrameInterval | ||
| : frame->dwFrameInterval[0]; | ||
| /* Compute a bandwidth estimation by multiplying the frame | ||
| * size by the number of video frames per second, divide the | ||
| * result by the number of USB frames (or micro-frames for | ||
| * high-speed devices) per second and add the UVC header size | ||
| * (assumed to be 12 bytes long). | ||
| */ | ||
| bandwidth = frame->wWidth * frame->wHeight / 8 * format->bpp; | ||
| bandwidth *= 10000000 / interval + 1; | ||
| bandwidth /= 1000; | ||
| if (stream->dev->udev->speed == USB_SPEED_HIGH) | ||
| bandwidth /= 8; | ||
| bandwidth += 12; | ||
| /* The bandwidth estimate is too low for many cameras. Don't use | ||
| * maximum packet sizes lower than 1024 bytes to try and work | ||
| * around the problem. According to measurements done on two | ||
| * different camera models, the value is high enough to get most | ||
| * resolutions working while not preventing two simultaneous | ||
| * VGA streams at 15 fps. | ||
| */ | ||
| bandwidth = max_t(u32, bandwidth, 1024); | ||
| ctrl->dwMaxPayloadTransferSize = bandwidth; | ||
| } | ||
| if(format->flags & UVC_FMT_FLAG_COMPRESSED){ctrl->dwMaxPayloadTransferSize = 0x400;}//meekdai | ||
| } | ||
| ``` | ||
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| 重新编译好代码下载固件后，执行下面的代码就可以用2个摄像头以MJPEG格式推流了。 | ||
| ``` | ||
| mjpg_streamer -i "input_uvc.so -d /dev/video0 -f 10 -n -r 1920x1080" -o "output_http.so -p 8080 -w /usr/www" & mjpg_streamer -i "input_uvc.so -d /dev/video1 -f 10 -n -r 1920x1080" -o "output_http.so -p 8081 -w /usr/www" | ||
| ``` | ||
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