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• OpenCV 4.5.2 takes a long time (>100ms) to retrieve a single frame from a webcam, C++ on Windows 10

  9 juin 2021, par Mustard Tiger

  I've been having a tough time getting my webcam working quickly with opencv. Frames take a very long time to read, (a recorded average of 124ms across 500 frames) I've tried on three different computers (running Windows 10) with a logitech C922 webcam. The most recent machine I tested on has a Ryzen 9 3950X, with 32gbs of ram ; no lack of power.

  


  Here is the code :

  


  cv::VideoCapture cap = cv::VideoCapture(m_cameraNum);&#xA;&#xA;// Check if camera opened successfully&#xA;if (!cap.isOpened())&#xA;{&#xA;    m_logger->critical("Error opening video stream or file\n\r");&#xA;    return -1;&#xA;}&#xA;&#xA;bool result = true;&#xA;result &amp;= cap.set(cv::CAP_PROP_FRAME_WIDTH, 1280);&#xA;result &amp;= cap.set(cv::CAP_PROP_FRAME_HEIGHT, 720);&#xA;&#xA;bool ready = false;&#xA;std::vector<string> timeLog;&#xA;timeLog.reserve(50000);&#xA;int i = 0;&#xA;&#xA;while (i &lt; 500)&#xA;{&#xA;    auto start = std::chrono::system_clock::now();&#xA;    &#xA;    cv::Mat img;&#xA;    ready = cap.read(img);&#xA;&#xA;    // If the frame is empty, break immediately&#xA;    if (!ready)&#xA;    {&#xA;        timeLog.push_back("continue");&#xA;        continue;&#xA;    }&#xA;&#xA;    i&#x2B;&#x2B;;&#xA;    auto end = std::chrono::system_clock::now();&#xA;    timeLog.push_back(std::to_string(std::chrono::duration_cast(end - start).count()));&#xA;}&#xA;&#xA;for (auto&amp; entry : timeLog)&#xA;    m_logger->info(entry);&#xA;&#xA;cap.release();&#xA;return 0;&#xA;</string>

  


  Notice that I write the elapsed time to a log file at the end of execution. The average time is 124ms for debug and release, and not one instance of "continue" after half a dozen runs.

  


  It doesn't matter if I use USB 2 or USB 3 ports (the camera is USB2) or if I run a debug build or a release build, the log file will show anywhere from 110ms to 130ms of time for each frame. The camera works fine in other app, OBS can get a smooth 1080@30fps or 720@60fps.

  


  Stepping through the debugger and doing a lot of Googling, I've learned the following about my system :

  


  

  • The backend chosen by default is DSHOW. GStreamer and FFMPEG are also available.

  


  • DSHOW uses FFMPEG somehow (it needs the FFMPEG dll) but I cannot use FFMPEG directly through opencv. Attempting to use cv::VideoCapture(m_cameraNum, cv::CAP_FFMPEG) always fails. It seems like Opencv's interface to FFMPEG is only capable of opening video files.

  


  • Microsoft really screwed up camera devices in Windows a few years back, not sure if this is related to my problem.

  


  


  Here's a short list of the fixes I have tried, most taken from older SO posts :

  


  

  • result &= cap.set(cv::CAP_PROP_FRAME_COUNT, 30) ; // Returns false, does nothing

  


  • result &= cap.set(cv::CAP_PROP_CONVERT_RGB, 0) ; // Returns true, does nothing

  


  • result &= cap.set(cv::CAP_PROP_MODE, cv::VideoWriter::fourcc('M', 'J', 'P', 'G')) ; // Returns false, does nothing

  


  • Set registry key from http://alax.info/blog/1693 that should disable the new Windows camera server.

  


  • Updated from 4.5.0 to 4.5.2, no change.

  


  • Asked device manager to find a newer driver, no newer driver found.

  


  


  I'm out of ideas. Any help ?

  


• ffmpeg capture output from child window

  3 janvier 2013, par glitchyme

  using xwininfo -all I'm able to see the stats of any window, along with its child windows

  xwininfo: Window id: 0x3c000ba "Electro - The Slag & Prototype Raptor - Crescendo - YouTube - Mozilla Firefox"
  
  
  
    Root window id: 0xa8 (the root window) (has no name)
  
    Parent window id: 0xc001b8 (has no name)
  
       2 children:
  
       0x3c00175 (has no name): ()  1388x876+0+0  +52+24
  
          5 children:
  
          0x3d210ab (has no name): ()  854x510+225+197  +277+221
  
             1 child:
  
             0x3d210ac (has no name): ()  854x510+0+0  +277+221
  
                1 child:
  
                0x40404de "plugin-container": ("plugin-container" "Plugin-container")  854x510+0+0  +277+221
  
                   2 children:
  
                   0x40404e1 (has no name): ()  854x510+0+0  +277+221
  
                   0x40404df (has no name): ()  1x1+-1+-1  +276+220
  
          0x3ddbcf2 (has no name): ()  640x390+225+162  +277+186
  
             1 child:
  
             0x3ddbcf3 (has no name): ()  640x390+0+0  +277+186
  
                1 child:
  
                0x403d545 "plugin-container": ("plugin-container" "Plugin-container")  640x390+0+0  +277+186
  
                   2 children:
  
                   0x403d548 (has no name): ()  640x390+0+0  +277+186
  
                   0x403d546 (has no name): ()  1x1+-1+-1  +276+185
  
          0x3dac7f9 (has no name): ()  640x390+225+162  +277+186
  
             1 child:
  
             0x3dac7fa (has no name): ()  640x390+0+0  +277+186
  
                1 child:
  
                0x4039d8b "plugin-container": ("plugin-container" "Plugin-container")  640x390+0+0  +277+186
  
                   2 children:
  
                   0x4039d8e (has no name): ()  640x390+0+0  +277+186
  
                   0x4039d8c (has no name): ()  1x1+-1+-1  +276+185
  
          0x3c3f939 (has no name): ()  640x390+225+197  +277+221
  
             1 child:
  
             0x3c3f93a (has no name): ()  640x390+0+0  +277+221
  
                1 child:
  
                0x4011918 "plugin-container": ("plugin-container" "Plugin-container")  640x390+0+0  +277+221
  
                   2 children:
  
                   0x401191b (has no name): ()  640x390+0+0  +277+221
  
                   0x4011919 (has no name): ()  1x1+-1+-1  +276+220
  
          0x3c0d1dc (has no name): ()  1x1+0+97  +52+121
  
             1 child:
  
             0x3c0d1dd (has no name): ()  1x1+0+0  +52+121
  
                1 child:
  
                0x4002c1e "plugin-container": ("plugin-container" "Plugin-container")  1x1+0+0  +52+121
  
                   2 children:
  
                   0x4002c40 (has no name): ()  1x1+0+0  +52+121
  
                   0x4002c1f (has no name): ()  1x1+-1+-1  +51+120
  
       0x3c000bb (has no name): ()  1x1+-1+-1  +51+23
  
  
  
    Absolute upper-left X:  52
  
    Absolute upper-left Y:  24
  
    Relative upper-left X:  0
  
    Relative upper-left Y:  0
  
    Width: 1388
  
    Height: 876
  
    Depth: 24
  
    Visual: 0x23
  
    Visual Class: TrueColor
  
    Border width: 0
  
    Class: InputOutput
  
    Colormap: 0x20 (installed)
  
    Bit Gravity State: NorthWestGravity
  
    Window Gravity State: NorthWestGravity
  
    Backing Store State: NotUseful
  
    Save Under State: no
  
    Map State: IsViewable
  
    Override Redirect State: no
  
    Corners:  +52+24  -0+24  -0-0  ç0
  
    -geometry 1388x876-0-0
  
  
  
    Bit gravity: NorthWestGravity
  
    Window gravity: NorthWestGravity
  
    Backing-store hint: NotUseful
  
    Backing-planes to be preserved: 0xffffffff
  
    Backing pixel: 0
  
    Save-unders: No
  
  
  
    Someone wants these events:
  
        KeyPress
  
        KeyRelease
  
        ButtonPress
  
        ButtonRelease
  
        EnterWindow
  
        LeaveWindow
  
        PointerMotion
  
        Exposure
  
        VisibilityChange
  
        StructureNotify
  
        FocusChange
  
        PropertyChange
  
    Do not propagate these events:
  
    Override redirection?: No
  
  
  
    Window manager hints:
  
        Client accepts input or input focus: Yes
  
        Initial state is Normal State
  
        Displayed on desktop 0
  
        Window type:
  
            Normal
  
        Window state:
  
            Maximized Vert
  
            Maximized Horz
  
        Process id: 4087 on host jb
  
        Frame extents: 0, 0, 0, 0
  
  
  
    Normal window size hints:
  
        Program supplied minimum size: 18 by 97
  
        Program supplied maximum size: 1073741824 by 1073741824
  
        Program supplied window gravity: NorthWestGravity
  
    No zoom window size hints defined
  
  
  
    No window shape defined
  
    No border shape defined

  However, if I try capturing from the screen given the size and offset of the child window, then I risk losing data when another window floats ontop of it, I switch to another tab while recording, I resize the child window, or move the child window. Instead, I'd like to use ffmpeg to capture from specifically that child window.

  Ideas ? Tips ? Maybe some other hacks to accomplish this ? Thanks :)

• Monster Battery Power Revisited

  28 mai 2010, par Multimedia Mike — Python, Science Projects

  So I have this new fat netbook battery and I performed an experiment to determine how long it really lasts. In my last post on the matter, it was suggested that I should rely on the information that gnome-power-manager is giving me. However, I have rarely seen GPM report more than about 2 hours of charge ; even on a full battery, it only reports 3h25m when I profiled it as lasting over 5 hours in my typical use. So I started digging to understand how GPM gets its numbers and determine if, perhaps, it’s not getting accurate data from the system.

  I started poking around /proc for the data I wanted. You can learn a lot in /proc as long as you know the right question to ask. I had to remember what the power subsystem is called — ACPI — and this led me to /proc/acpi/battery/BAT0/state which has data such as :

  present :                 yes
  capacity state :          ok
  charging state :          charged
  present rate :            unknown
  remaining capacity :      100 mAh
  present voltage :         8326 mV
  

  "Remaining capacity" rated in mAh is a little odd ; I would later determine that this should actually be expressed as a percentage (i.e., 100% charge at the time of this reading). Examining the GPM source code, it seems to determine as a function of the current CPU load (queried via /proc/stat) and the battery state queried via a facility called devicekit. I couldn’t immediately find any source code to the latter but I was able to install a utility called ’devkit-power’. Mostly, it appears to rehash data already found in the above /proc file.

  Curiously, the file /proc/acpi/battery/BAT0/info, which displays essential information about the battery, reports the design capacity of my battery as only 4400 mAh which is true for the original battery ; the new monster battery is supposed to be 10400 mAh. I can imagine that all of these data points could be conspiring to under-report my remaining battery life.

  Science project : Repeat the previous power-related science project but also parse and track the remaining capacity and present voltage fields from the battery state proc file.

  Let’s skip straight to the results (which are consistent with my last set of results in terms of longevity) :

  
  
  

  So there is definitely something strange going on with the reporting— the 4400 mAh battery reports discharge at a linear rate while the 10400 mAh battery reports precipitous dropoff after 60%.

  Another curious item is that my script broke at first when there was 20% power remaining which, as you can imagine, is a really annoying time to discover such a bug. At that point, the "time to empty" reported by devkit-power jumped from 0 seconds to 20 hours (the first state change observed for that field).

  Here’s my script, this time elevated from Bash script to Python. It requires xdotool and devkit-power to be installed (both should be available in the package manager for a distro).
  

  PLAIN TEXT

  PYTHON :

  1. # !/usr/bin/python
  2.  
  3. import commands
  4. import random
  5. import sys
  6. import time
  7.  
  8. XDOTOOL = "/usr/bin/xdotool"
  9. BATTERY_STATE = "/proc/acpi/battery/BAT0/state"
  10. DEVKIT_POWER = "/usr/bin/devkit-power -i /org/freedesktop/DeviceKit/Power/devices/battery_BAT0"
  11.  
  12. print "count, unixtime, proc_remaining_capacity, proc_present_voltage, devkit_percentage, devkit_voltage"
  13.  
  14. count = 0
  15. while 1 :
  16.   commands.getstatusoutput("%s mousemove %d %d" % (XDOTOOL, random.randrange(0,800), random.randrange(0, 480)))
  17.   battery_state = open(BATTERY_STATE).read().splitlines()
  18.   for line in battery_state :
  19.     if line.startswith("remaining capacity :") :
  20.       proc_remaining_capacity = int(line.lstrip("remaining capacity : ").rstrip("mAh"))
  21.     elif line.startswith("present voltage :") :
  22.       proc_present_voltage = int(line.lstrip("present voltage : ").rstrip("mV"))
  23.   devkit_state = commands.getoutput(DEVKIT_POWER).splitlines()
  24.   for line in devkit_state :
  25.     line = line.strip()
  26.     if line.startswith("percentage :") :
  27.       devkit_percentage = int(line.lstrip("percentage :").rstrip(’\%’))
  28.     elif line.startswith("voltage :") :
  29.       devkit_voltage = float(line.lstrip("voltage :").rstrip(’V’)) * 1000
  30.   print "%d, %d, %d, %d, %d, %d" % (count, time.time(), proc_remaining_capacity, proc_present_voltage, devkit_percentage, devkit_voltage)
  31.   sys.stdout.flush()
  32.   time.sleep(60)
  33.   count += 1