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长沙红胖子Qt（长沙创微智科）博文大全：开发技术集合（包含Qt实用技术、树莓派、三维、OpenCV、OpenGL、ffmpeg、OSG、单片机、软硬结合等等）持续更新中…

FFmpeg、SDL和流媒体开发专栏

上一篇：《GStreamer开发笔记（二）：GStreamer在ubnutn平台部署安装，测试gstreamer/cheese/ffmpeg/fmplayer打摄像头延迟和内存》
下一篇：持续补充中…

前言

  前面测试了多种技术路线，本篇补全剩下的2种主流技术，v4l2+sdl2（偏底层），v4l2+QtOpengl（应用），v4l2+ffmpeg+QtQImage（Image的方式转图低于1ms，但是从yuv格式转到rgb格式需要ffmpeg进行转码耗时）。

Demo

  

注意

  存在色彩空间不准确，不进行细究。

延迟和内存对比

步骤一：v4l2代码测试延迟和内存

  没有找到命令行，只找到了v4l2-ctl可以查看和控制摄像头的参数。
  看gsteamer的源头就是v4l2src，随手写个代码使用v4l2打开摄像头查看延迟，其中v4l2是个框架负责操作和捕获，无法直接进行渲染显示，本次使用了SDL进行显示。
  注意：这里不对v4l2介绍，会有专门的专栏去讲解v4l2的多媒体开发，但是这里使用v4l2的代码写个简单的程序来打开。

sudo apt-get install libsdl2-dev libsdl2-2.0-0

  然后写代码，代码贴在Demo里面
  

  

步骤二：v4l2+QtOpenGL+memcpy复制一次

  

  查看内存：
  

步骤三：v4l2+QtOpenGL+共享内存

  

最终总结

  到这里，我们得出结论，gstreamer基本是最优秀的框架之一了，初步测试不是特别严谨，但是基本能反应情况（比如ffmpeg得fmplay本轮测试是最差，但是ffmpeg写代码可以进行ffmpeg源码和编程代码的优化，达到150ms左右，诸如这类情况不考虑）。
  V4l2+SDL优于gstreamer优于ffmplayer优于v4l2+QtOpenGL优于cheese优于ffmpeg。
  其中v4l2+SDL、gstreamer、fmplayer在内存占用上有点区别，延迟差不多130ms左右。Cheese和v4l2+QtOpenGL延迟差不多
到170ms。Ffmpeg的播放器延迟到500ms左右。

扩展

  这里要注意，大部分低延迟内窥镜笔者接触的都是buffer叠显存的方式，少数厂家使用v4l2+QtOpenGL的方式，经过测试慢了一帧左右。

Demo：V4l2+SDL

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <linux/videodev2.h>
#include <errno.h>
#include <SDL2/SDL.h>
#include <SDL2/SDL_pixels.h>#define WIDTH 640
#define HEIGHT 480int main() {setbuf(stdout, NULL);int fd;struct v4l2_format fmt;struct v4l2_requestbuffers req;struct v4l2_buffer buf;void *buffer_start;unsigned int buffer_length;// 打开摄像头设备fd = open("/dev/video0", O_RDWR);if (fd == -1) {perror("打开摄像头设备失败");return EXIT_FAILURE;}// 设置视频格式memset(&fmt, 0, sizeof(fmt));fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;fmt.fmt.pix.width = WIDTH;fmt.fmt.pix.height = HEIGHT;fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV;fmt.fmt.pix.field = V4L2_FIELD_INTERLACED;if (ioctl(fd, VIDIOC_S_FMT, &fmt) == -1) {perror("设置视频格式失败");close(fd);return EXIT_FAILURE;}// 请求缓冲区memset(&req, 0, sizeof(req));req.count = 1;req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;req.memory = V4L2_MEMORY_MMAP;if (ioctl(fd, VIDIOC_REQBUFS, &req) == -1) {perror("请求缓冲区失败");close(fd);return EXIT_FAILURE;}// 映射缓冲区memset(&buf, 0, sizeof(buf));buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;buf.memory = V4L2_MEMORY_MMAP;buf.index = 0;if (ioctl(fd, VIDIOC_QUERYBUF, &buf) == -1) {perror("查询缓冲区失败");close(fd);return EXIT_FAILURE;}buffer_length = buf.length;buffer_start = mmap(NULL, buffer_length, PROT_READ | PROT_WRITE, MAP_SHARED, fd, buf.m.offset);if (buffer_start == MAP_FAILED) {perror("映射缓冲区失败");close(fd);return EXIT_FAILURE;}// 将缓冲区放入队列if (ioctl(fd, VIDIOC_QBUF, &buf) == -1) {perror("缓冲区入队失败");munmap(buffer_start, buffer_length);close(fd);return EXIT_FAILURE;}// 开始视频捕获enum v4l2_buf_type type = V4L2_BUF_TYPE_VIDEO_CAPTURE;if (ioctl(fd, VIDIOC_STREAMON, &type) == -1) {perror("开始视频捕获失败");munmap(buffer_start, buffer_length);close(fd);return EXIT_FAILURE;}// 初始化 SDLif (SDL_Init(SDL_INIT_VIDEO) < 0) {fprintf(stderr, "SDL 初始化失败: %s\n", SDL_GetError());munmap(buffer_start, buffer_length);close(fd);return EXIT_FAILURE;}SDL_Window *window = SDL_CreateWindow("V4L2 Camera", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, WIDTH, HEIGHT, 0);if (!window) {fprintf(stderr, "创建 SDL 窗口失败: %s\n", SDL_GetError());SDL_Quit();munmap(buffer_start, buffer_length);close(fd);return EXIT_FAILURE;}SDL_Renderer *renderer = SDL_CreateRenderer(window, -1, 0);// SDL_PIXELFORMAT_YV12 =      /**< Planar mode: Y + V + U  (3 planes) */// SDL_PIXELFORMAT_IYUV =      /**< Planar mode: Y + U + V  (3 planes) */// SDL_PIXELFORMAT_YUY2 =      /**< Packed mode: Y0+U0+Y1+V0 (1 plane) */// SDL_PIXELFORMAT_UYVY =      /**< Packed mode: U0+Y0+V0+Y1 (1 plane) */// SDL_PIXELFORMAT_YVYU =      /**< Packed mode: Y0+V0+Y1+U0 (1 plane) *///    SDL_Texture *texture = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_YV12, SDL_TEXTUREACCESS_STREAMING, WIDTH, HEIGHT);
//    SDL_Texture *texture = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_IYUV, SDL_TEXTUREACCESS_STREAMING, WIDTH, HEIGHT);SDL_Texture *texture = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_YUY2, SDL_TEXTUREACCESS_STREAMING, WIDTH, HEIGHT);
//    SDL_Texture *texture = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_UYVY, SDL_TEXTUREACCESS_STREAMING, WIDTH, HEIGHT);
//    SDL_Texture *texture = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_YVYU, SDL_TEXTUREACCESS_STREAMING, WIDTH, HEIGHT);int running = 1;SDL_Event event;while (running) {// 处理事件while (SDL_PollEvent(&event)) {if (event.type == SDL_QUIT) {running = 0;}}// 捕获帧memset(&buf, 0, sizeof(buf));buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;buf.memory = V4L2_MEMORY_MMAP;if (ioctl(fd, VIDIOC_DQBUF, &buf) == -1) {perror("出队缓冲区失败");break;}// 更新 SDL 纹理SDL_UpdateTexture(texture, NULL, buffer_start, WIDTH);// 渲染纹理SDL_RenderClear(renderer);SDL_RenderCopy(renderer, texture, NULL, NULL);SDL_RenderPresent(renderer);// 将缓冲区重新入队if (ioctl(fd, VIDIOC_QBUF, &buf) == -1) {perror("缓冲区入队失败");break;}}// 清理资源SDL_DestroyTexture(texture);SDL_DestroyRenderer(renderer);SDL_DestroyWindow(window);SDL_Quit();munmap(buffer_start, buffer_length);close(fd);return EXIT_SUCCESS;
}

Demo：V4l2+QtOpenGL+共享内存

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <linux/videodev2.h>
#include <errno.h>
#include "DisplayOpenGLWidget.h"
#include <QApplication>
#include <QElapsedTimer>#define WIDTH 640
#define HEIGHT 480#include <QDebug>
#include <QDateTime>
//#define LOG qDebug()<<__FILE__<<__LINE__
//#define LOG qDebug()<<__FILE__<<__LINE__<<__FUNCTION__
//#define LOG qDebug()<<__FILE__<<__LINE__<<QThread()::currentThread()
//#define LOG qDebug()<<__FILE__<<__LINE__<<QDateTime::currentDateTime().toString("yyyy-MM-dd")
#define LOG qDebug()<<__FILE__<<__LINE__<<QDateTime::currentDateTime().toString("yyyy-MM-dd hh:mm:ss:zzz")int main(int argc, char *argv[])
{QApplication a(argc, argv);DisplayOpenGLWidget displayOpenGLWidget;displayOpenGLWidget.show();setbuf(stdout, NULL);int fd;struct v4l2_format fmt;struct v4l2_requestbuffers req;struct v4l2_buffer buf;void *buffer_start;unsigned int buffer_length;// 打开摄像头设备fd = open("/dev/video0", O_RDWR);if (fd == -1) {perror("打开摄像头设备失败");return EXIT_FAILURE;}// 设置视频格式memset(&fmt, 0, sizeof(fmt));fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;fmt.fmt.pix.width = WIDTH;fmt.fmt.pix.height = HEIGHT;fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV;fmt.fmt.pix.field = V4L2_FIELD_INTERLACED;if (ioctl(fd, VIDIOC_S_FMT, &fmt) == -1) {perror("设置视频格式失败");close(fd);return EXIT_FAILURE;}// 请求缓冲区memset(&req, 0, sizeof(req));req.count = 1;req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;req.memory = V4L2_MEMORY_MMAP;if (ioctl(fd, VIDIOC_REQBUFS, &req) == -1) {perror("请求缓冲区失败");close(fd);return EXIT_FAILURE;}// 映射缓冲区memset(&buf, 0, sizeof(buf));buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;buf.memory = V4L2_MEMORY_MMAP;buf.index = 0;if (ioctl(fd, VIDIOC_QUERYBUF, &buf) == -1) {perror("查询缓冲区失败");close(fd);return EXIT_FAILURE;}buffer_length = buf.length;buffer_start = mmap(NULL, buffer_length, PROT_READ | PROT_WRITE, MAP_SHARED, fd, buf.m.offset);if (buffer_start == MAP_FAILED) {perror("映射缓冲区失败");close(fd);return EXIT_FAILURE;}displayOpenGLWidget.initDrawBuffer(WIDTH, HEIGHT, true, (char *)buffer_start);// 将缓冲区放入队列if (ioctl(fd, VIDIOC_QBUF, &buf) == -1) {perror("缓冲区入队失败");munmap(buffer_start, buffer_length);close(fd);return EXIT_FAILURE;}// 开始视频捕获enum v4l2_buf_type type = V4L2_BUF_TYPE_VIDEO_CAPTURE;if (ioctl(fd, VIDIOC_STREAMON, &type) == -1) {perror("开始视频捕获失败");munmap(buffer_start, buffer_length);close(fd);return EXIT_FAILURE;}int running = 1;while (running) {// 捕获帧memset(&buf, 0, sizeof(buf));buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;buf.memory = V4L2_MEMORY_MMAP;if (ioctl(fd, VIDIOC_DQBUF, &buf) == -1) {perror("出队缓冲区失败");break;}// 渲染
//        memcpy(drawBuffer, buffer_start, buffer_length);displayOpenGLWidget.displayVideoFrame();QApplication::processEvents();QApplication::processEvents();QApplication::processEvents();// 将缓冲区重新入队if (ioctl(fd, VIDIOC_QBUF, &buf) == -1) {perror("缓冲区入队失败");break;}}// 清理资源munmap(buffer_start, buffer_length);close(fd);return EXIT_SUCCESS;
}

入坑

入坑一：v4l2打开视频代码不对

问题

  V4l2打开视频代码数据错位
  

原因

  纹理格式不同，但是笔者测试了SDL所有支持的，都不行，不钻了，是需要进行色彩空间转换下才可以（会额外消耗一定延迟，预估10ms以内），我们选个可以的，测试延迟内存即可。

// SDL_PIXELFORMAT_YV12 =      /**< Planar mode: Y + V + U  (3 planes) */
// SDL_PIXELFORMAT_IYUV =      /**< Planar mode: Y + U + V  (3 planes) */
// SDL_PIXELFORMAT_YUY2 =      /**< Packed mode: Y0+U0+Y1+V0 (1 plane) */
// SDL_PIXELFORMAT_UYVY =      /**< Packed mode: U0+Y0+V0+Y1 (1 plane) */
// SDL_PIXELFORMAT_YVYU =      /**< Packed mode: Y0+V0+Y1+U0 (1 plane) *///    SDL_Texture *texture = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_YV12, SDL_TEXTUREACCESS_STREAMING, WIDTH, HEIGHT);
//    SDL_Texture *texture = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_IYUV, SDL_TEXTUREACCESS_STREAMING, WIDTH, HEIGHT);
SDL_Texture *texture = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_YUY2, SDL_TEXTUREACCESS_STREAMING, WIDTH, HEIGHT);
//    SDL_Texture *texture = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_UYVY, SDL_TEXTUREACCESS_STREAMING, WIDTH, HEIGHT);
//    SDL_Texture *texture = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_YVYU, SDL_TEXTUREACCESS_STREAMING, WIDTH, HEIGHT);

解决

  不解决，选择能看清楚的就好了。

上一篇：《GStreamer开发笔记（二）：GStreamer在ubnutn平台部署安装，测试gstreamer/cheese/ffmpeg/fmplayer打摄像头延迟和内存》
下一篇：持续补充中…

本文章博客地址：https://blog.csdn.net/qq21497936/article/details/147714800