V4L2 帧率下降

Question

上下文

您好！我一直在为一个机器人项目开发软件，该项目将使用视觉作为主要感官之一。我一直在围绕 Raspberry Pi 3 运行 Raspbian Jessie Lite 和内核 4.9.35-v7+ 构建系统。除了其他车载传感器外，我还计划根据摄像头记录的驾驶数据训练一些 ML 模型。为了检索视频帧，我使用 v4l2 api 和 a Minoru 3D USB webcam. The source for my project can be found at https://github.com/mrpossoms/AVC2017。

问题

这真是一个奇怪的问题。我上面描述的工作正常，除了帧速率从目标 15fps 显着下降，但只有当它看着一个超过 1 米远的物体时！我录制了一个视频 here 来展示这个问题。首先，我将手非常靠近相机，您可以在终端中看到帧速率从理想的 15fps 开始。然而，当我慢慢移开我的手时，帧率下降到 7fps 左右！

这是我的相机代码：

#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <string.h>
#include <strings.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <assert.h>

#include "structs.h"
#include "cam.h"

#define CAM_FPS 5

cam_t cam_open(const char* path, cam_settings_t* cfg)
{

    int fd = open(path, O_RDWR);
    int res;

    if(fd < 0)
    {
        fprintf(stderr, "Error opening video device '%s'\n", path);
        //exit(-1);

        cam_t empty = {};
        return empty;
    }

    struct v4l2_capability cap;
    res = ioctl(fd, VIDIOC_QUERYCAP, &cap);
    if(res < 0)
    {
        fprintf(stderr, "Error: %d querying '%s' for capabilities (%d)\n", res, path, errno);
        exit(-2);
    }

    if(!(cap.capabilities & V4L2_CAP_VIDEO_CAPTURE))
    {
        fprintf(stderr, "Error: '%s' lacks V4L2_CAP_VIDEO_CAPTURE capability\n", path);
    }

    res = cam_config(fd, cfg);
    if(res < 0)
    {
        fprintf(stderr, "Error: %d configuring '%s' (%d)\n", res, path, errno);
        exit(-3);
    }

    // Inform v4l about the buffers we want to receive data through
    struct v4l2_requestbuffers bufrequest = {};
    bufrequest.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    bufrequest.memory = V4L2_MEMORY_MMAP;
    bufrequest.count = 2;

    if(ioctl(fd, VIDIOC_REQBUFS, &bufrequest) < 0)
    {
        fprintf(stderr, "VIDIOC_REQBUFS\n");
        exit(-4);
    }


    if(bufrequest.count < 2)
    {
        fprintf(stderr, "Not enough memory\n");
        exit(-5);
    }


    struct v4l2_buffer bufferinfo = {};
    void** fbs = calloc(sizeof(void*), bufrequest.count);
    for(int i = bufrequest.count; i--;)
    {
        bufferinfo.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
        bufferinfo.memory = V4L2_MEMORY_MMAP;
        bufferinfo.index = i;

        if(ioctl(fd, VIDIOC_QUERYBUF, &bufferinfo) < 0)
        {
            fprintf(stderr, "VIDIOC_QUERYBUF\n");
            exit(-5);
        }

        fbs[i] = mmap(
            NULL,
            bufferinfo.length,
            PROT_READ | PROT_WRITE,
            MAP_SHARED,
            fd,
            bufferinfo.m.offset
        );

        if(fbs[i] == MAP_FAILED)
        {
            fprintf(stderr, "mmap failed\n");
            exit(-6);
        }

        bzero(fbs[i], bufferinfo.length);
        ioctl(fd, VIDIOC_QBUF, &bufferinfo);
    }


    cam_t cam = {
        .fd = fd,
        .frame_buffers = fbs,
        .buffer_info = bufferinfo,
    };

    cam_wait_frame(&cam);

    int type = bufferinfo.type;
    if(ioctl(fd, VIDIOC_STREAMON, &type) < 0)
    {
        fprintf(stderr, "Error starting streaming\n");
        exit(-7);
    }

    return cam;
}


int cam_request_frame(cam_t* cam)
{
    cam->buffer_info.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    cam->buffer_info.memory = V4L2_MEMORY_MMAP;

    return ioctl(cam->fd, VIDIOC_QBUF, &cam->buffer_info);
}


int cam_wait_frame(cam_t* cam)
{
    ioctl(cam->fd, VIDIOC_DQBUF, &cam->buffer_info);
}


int cam_config(int fd, cam_settings_t* cfg)
{
    int res = 0;
    struct v4l2_format format;

    if(!cfg)
    {
        fprintf(stderr, "Error: null configuration provided\n");
        return -1;
    }

/*
    res = ioctl(fd, VIDIOC_G_FMT, &format);
    if(res < 0)
    {
        fprintf(stderr, "Error: failed retrieving camera settings (%d)\n", errno);
        return -2;
    }
*/

    format.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    format.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV;
    format.fmt.pix.width = cfg->width;
    format.fmt.pix.height = cfg->height;

    if(ioctl(fd, VIDIOC_S_FMT, &format) < 0)
    {
        fprintf(stderr, "Error: failed applying camera settings\n");
        return -3;
    }

    struct v4l2_streamparm parm = {};

    parm.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

    parm.parm.capture.timeperframe.numerator = 1;
    parm.parm.capture.timeperframe.denominator = 15;

    res = ioctl(fd, VIDIOC_S_PARM, &parm);

    return 0;
}

我可以 100% 地重现问题，但我真的不知道是什么导致了这种行为。非常感谢任何建议或想法。

Answer 1

正如马克所说，问题出在曝光上。驱动程序必须决定在较暗的情况下每帧需要更多的曝光时间。只需将相机带到室外即可立即将帧速率提高到目标 15fps。

V4L2 帧率下降

V4L2 Framerate Drops

c

linux

raspberry-pi3

robotics

v4l2

上下文

问题