避免视频捕获延迟的 gocv 实用技巧

在使用 GoCV 录制视频时，指定分辨率可能会导致视频捕获延迟。当未指定分辨率时，捕获效果良好，但设置图像大小后，会产生延时摄影，因为网络摄像头将多次录制，并将整个捕获时间填充到所需的视频长度。要避免这种情况，可以尝试设置 fps 标志，例如 webcam.Set(5, 30)，其中 5 是 fps 标志。这可以帮助确保以所需的帧速率捕获视频，从而消除延迟摄影。

我想捕获并保存 mjpeg 格式的视频文件，并将分辨率设置为 1920x1080p。当我不指定分辨率时，捕获效果很好，我可以以 30fps 的速度录制和播放。但如果我改变记录的图像大小，我会得到一个延时摄影。网络摄像头会根据需要进行多次录制，并将整个捕获时间放入所需的视频长度中。例如，网络摄像头应以 30fps 录制 120 帧，因此视频捕获以及录制的视频长度应持续 4 秒。相反，捕获持续约 20 秒。整个 20 秒都在 4 秒内，这就产生了延时摄影。我怎样才能避免这种情况？我是否使用了错误的命令来定义分辨率？这是我的代码，我已经尝试过“webcam.set(3, 1920)”等以及 gocv.newmat() 或 newmatwithsize(...)。以下是我的代码

/*-------------------------------------------- savevideotest.go -----
|
|  Created  -
|
|  Version 1.0  2021-01-03      Initial version
|------------------------------------------------------------------
|  Version -    -               -
|------------------------------------------------------------------
|  Purpose:     Video capture tool
|               Video Capture Tool to be used as main tool when it comes
|               to recording videos with the raspberry pi
*-------------------------------------------------------------------*/
package main

import (
    "flag"
    "fmt"
    "gocv.io/x/gocv"
    "strconv"
    "strings"
    "sync"
    "time"
    "github.com/op/go-logging"
    "os"
)
var(
    videolength = 120       //videolength in frames (recording with 25fps). 15k = 10min
    framecheck [2]int
    videoformat *string
    location  *string
    camcount *int
    path *string
    log = logging.MustGetLogger("example")
    format = logging.MustStringFormatter(`%{color} %{time:2006:Jan:2:15:04:05.000} %{shortfunc} > %{level:.4s} %{id:03x}%{color:reset} %{message}`) // Mon Jan 2 15:04:05 MST 2006 )
)



/*-------------------------------------------- init -----
|  Function init
|  Created      01.03.2021 - 
|  Last change  -- / ---- - --
|  Purpose:     Initialize flags for usage in other functions by parsing
|  Parameters:  ---
|  Returns:     ---
*-------------------------------------------------------------------*/
func init()  {
    videoformat = flag.String("videoformat",".avi","desired video format")
    location = flag.String("location", "BU_", "location of raspberry pi")
    camcount = flag.Int("camcount",1,"number of used cams")
    path = flag.String("path","","sets the path of videofile")
}

/*-------------------------------------------- main -----
|  Function main
|  Created      01.03.2021 - 
|  Last change  -- / ---- - --
|  Purpose:     main function, creating infinite recording loop
|               with error control(var framecheck) and log generation
|  Parameters:  ---
|  Returns:     ---
*-------------------------------------------------------------------*/
func main() {

    flag.Parse()

    printHeader()

    for {

        savevideo(videolength)
        //fmt.Printf("%v\n",framecheck)

        for k:= 0; k < *camcount; k++ {
            if framecheck[k] != videolength {
                fmt.Printf("Webcam %v hat nicht die geforderte Videolänge aufgenommen! Das Programm wird terminiert.", k)
                writeVideoLog(k)
                writeErrorLog(k)
                return
            }else {
                //framecheck[k] = 0
                writeVideoLog(k)
            }
        }

    }

}

/*-------------------------------------------- generateFileName -----
|  Function AddItem
|  Created      01.03.2021 -
|  Last change  -- / ---- - --
|  Purpose:     Function to generate the desired Filename by using flags
|  Parameters:  deviceID int
|  Returns:     filename.String
*-------------------------------------------------------------------*/
func generateFileName(j int) string {

    flag.Parse()


    var filename strings.Builder
    filename.WriteString(*path)
    filename.WriteString(*location)
    filename.WriteString("__")
    filename.WriteString("Cam")
    filename.WriteString(strconv.Itoa(j))
    filename.WriteString("__")
    filename.WriteString(time.Now().Format("20060102_150405"))
    filename.WriteString(*videoformat)
    return filename.String()
}



/*-------------------------------------------- saveVideo -----
|  Function saveVideo
|  Created      01.03.2021 -
|  Last change  -- / ---- - --
|  Purpose:     Function to record and save the video
|  Parameters:  videolength int
|  Returns:     ---
*-------------------------------------------------------------------*/
func savevideo(videolength int) {

    flag.Parse()


    var wg sync.WaitGroup
    wg.Add(*camcount)


    for j := 0; j < *camcount; j++ {

        go func(j int) {

            defer wg.Done()


            deviceID := j
            saveFile := generateFileName(j)


            webcam, err := gocv.VideoCaptureDevice(deviceID)//  OpenVideoCapture(deviceID)
            if err != nil {
                fmt.Printf("Error opening video capture device: %v\n", deviceID)
                return
            }


            defer webcam.Close()

            img := gocv.NewMatWithSize(1280, 720, gocv.MatTypeCV64F)
            defer img.Close()

            webcam.Set(3, 1280)
            webcam.Set(4, 780)


            if ok := webcam.Read(&img); !ok {
                fmt.Printf("Cannot read device %v\n", deviceID)
                return
            }



            writer, err := gocv.VideoWriterFile(saveFile, "MJPG", 30, 1280, 720, true)
            if err != nil {
                fmt.Printf("error opening video writer device: %v\n", saveFile)
                return
            }
            defer writer.Close()

            fmt.Printf("%v  %v  ", img.Cols(), img.Rows())

            for i := 0; i < videolength; i++ {
                if ok := webcam.Read(&img); !ok {
                    fmt.Printf("Device closed: %v\n", deviceID)
                    return
                }
                if img.Empty() {

                    continue
                }
                framecheck[j]++
                writer.Write(img)
            }

        }(j)

    }
    wg.Wait()

}

/*-------------------------------------------- printHeader -----
|  Function printHeader
|  Created      01.03.2021 -
|  Last change  -- / ---- - --
|  Purpose:     Function to print the header of the logfile
|  Parameters:  ---
|  Returns:     ---
*-------------------------------------------------------------------*/
func printHeader() {
    flag.Parse()
    file, err := os.OpenFile("logs.txt", os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0666)
    if err != nil {
        log.Fatal(err)
    }
    defer file.Close()

    backend1 := logging.NewLogBackend(file, "", 0)
    backend2 := logging.NewLogBackend(file, "", 0)
    // For messages written to backend2 we want to add some additional
    // information to the output, including the used log level and the name of
    // the function.
    backend2Formatter := logging.NewBackendFormatter(backend2, format)

    // Only errors and more severe messages should be sent to backend1
    backend1Leveled := logging.AddModuleLevel(backend1)
    backend1Leveled.SetLevel(logging.ERROR, "")

    // Set the backends to be used.
    logging.SetBackend(backend1Leveled, backend2Formatter)

    log.Info("|---------------|--------|---------------------------\n")
    log.Info("|BUSA VIDEO LOG |        |\n")
    log.Info("|---------------|--------|---------------------------\n")
    log.Info("|LOG SETUP      | INFO   | ROTATIONSIZE    800000000  [KBytes]]\n")
    log.Info("|               |        | Maximum size of Video directory\n")
    log.Info("|               |        | before old videos get deleted\n")
    log.Info("|               |--------|---------------------------\n")
    log.Info("|               | INFO   | MaxFileSizeLOG  500  [KBytes]\n")
    log.Info("|               |        | Maximum size of Logfile\n")
    log.Info("|               |        | before old logfiles get copied\n")
    log.Info("|               |        | away to BUSA_VIDEO.log.TIMESTAMP\n")
    log.Info("|               |--------|---------------------------\n")
    log.Info("|               | INFO   | MaxNumOldLOGS  10\n")
    log.Info("|               |        | Maximum number of old Logfiles\n")
    log.Info("|               |        | before oldest logfile get deleted\n")
    log.Info("|---------------|--------|---------------------------\n")
    log.Info("|LOCATION SETUP | INFO   | LOCATION_NAME " + *location + "\n")
    log.Info("|               |        | Name of Location\n")
    log.Info("|               |        | Used in filename\n")
    log.Info("|               |--------|---------------------------\n")
    log.Info("|               | INFO   | OBJECT_ID  1500021BU027-542~~~~~\n")
    log.Info("|               |        | ID for MQTT Topic to identify Object\n")
    log.Info("|               |        | where video are recorded\n")
    log.Info("|---------------|--------|---------------------------\n")
    log.Info("|MQTT SETUP     | INFO   | localIP  10.170.63.11\n")
    log.Info("|               |        | IP Addr that get used\n")
    log.Info("|               |        | in MQTT message for URL of Video\n")
    log.Info("|               |--------|---------------------------\n")
    log.Info("|               | INFO   | BUSA_MQTT_BROKER\n")
    log.Info("|               |        | MQTT Broker\n")
    log.Info("|               |--------|---------------------------\n")
    log.Info("|               | INFO   | BOX_ID  70820e1224c5\n")
    log.Info("|               |        | Hardware ID derived from MAC-Addr\n")
    log.Info("|---------------|--------|---------------------------\n")

}

/*-------------------------------------------- writeErrorLog -----
|  Function writeErrorLog
|  Created      01.03.2021 - 
|  Last change  -- / ---- - --
|  Purpose:     Function to print an error log entry in case something wents wrong
|  Parameters:  deviceID
|  Returns:     ---
*-------------------------------------------------------------------*/
func writeErrorLog(k int)  {
    flag.Parse()
    file, err := os.OpenFile("logs.txt", os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0666)
    if err != nil {
        log.Fatal(err)
    }
    defer file.Close()

    backend1 := logging.NewLogBackend(file, "", 0)
    backend2 := logging.NewLogBackend(file, "", 0)
    // For messages written to backend2 we want to add some additional
    // information to the output, including the used log level and the name of
    // the function.
    backend2Formatter := logging.NewBackendFormatter(backend2, format)

    // Only errors and more severe messages should be sent to backend1
    backend1Leveled := logging.AddModuleLevel(backend1)
    backend1Leveled.SetLevel(logging.ERROR, "")

    // Set the backends to be used.
    logging.SetBackend(backend1Leveled, backend2Formatter)

    log.Error("              | ERROR  | Kritischer Fehler: Webcam " + strconv.Itoa(k) + " hat nicht die erforderliche Anzahl an Frames aufgenommen. Die Anwendung wurde beendet.\n")

}

/*-------------------------------------------- writeVideoLog -----
|  Function writeVideoLog
|  Created      01.03.2021 -
|  Last change  -- / ---- - --
|  Purpose:     Function to write an info log entry when a video is saved
|  Parameters:  deviceID
|  Returns:     ---
*-------------------------------------------------------------------*/
func writeVideoLog(k int)  {
    flag.Parse()

    file, err := os.OpenFile("logs.txt", os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0666)
    if err != nil {
        log.Fatal(err)
    }
    defer file.Close()

    backend1 := logging.NewLogBackend(file, "", 0)
    backend2 := logging.NewLogBackend(file, "", 0)
    // For messages written to backend2 we want to add some additional
    // information to the output, including the used log level and the name of
    // the function.
    backend2Formatter := logging.NewBackendFormatter(backend2, format)

    // Only errors and more severe messages should be sent to backend1
    backend1Leveled := logging.AddModuleLevel(backend1)
    backend1Leveled.SetLevel(logging.ERROR, "")

    // Set the backends to be used.
    logging.SetBackend(backend1Leveled, backend2Formatter)

    log.Info("              | INFO   | Neues Video " + generateFileName(k) + "\n")
}

哦，是的，我对编码很陌生，尤其是 golang。我学习 java 一个月了，但作为实习生参与了一个 go 项目，以了解作为一名开发人员的意义。 （ps：我希望 deadprogram 能看到这一点，他似乎是 golang 和 gocv 中的神，他在我到目前为止查到的每个问题下：d）

解决方案

您是否尝试过设置 fps

webcam.Set(5, 30)

其中 5 是 fps 标志。

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