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• Encoding MJPEG from webcam in UWP development with C#

  24 avril 2018, par Federico Parra

  this is my first question in StackOverflow.

  How can I encode video being captured from webcam as a MJPEG using C# in UWP enviroment (Visual Studio 2017) ?
  Perhaps using FFMPEG or DirectShow ? Any particular bindings required to use them in UWP ?

  I’ve been through these walk-throughs trying to go the official way using MediaCapture :

  https://docs.microsoft.com/en-us/windows/uwp/audio-video-camera/basic-photo-video-and-audio-capture-with-mediacapture
  https://docs.microsoft.com/en-us/uwp/api/windows.media.capture.mediacapture

  According to Microsoft though, there is no MJPEG encoder included in MediaEncoder (only decoder) : https://docs.microsoft.com/en-us/windows/uwp/audio-video-camera/supported-codecs

  About FFMPEG UWP integration, I found this :
  https://github.com/Microsoft/FFmpegInterop
  https://blogs.windows.com/buildingapps/2015/06/05/using-ffmpeg-in-windows-applications/#HHYbWAVcM7LhkvYZ.97

  But it’s geared towards decoding, and I want to encode.

  Just in case someone is wondering, I want to use MJPEG for Two reasons :
  1) less CPU intensive (much less) because it doesn’t do inter-frame compression, means my Surface Pro (and other similar computers) will keep quiet without fans running like crazy
  2) I need all frames (i.e. not one every 30) to be crystal clear because of an algorithm I need to run on each of them after

  Any pointers would be greatly appreciated.

  Thank you,
  Federico

• Live video stream on server (PC) from images sent by robot through UDP

  3 février 2018, par Richard Knop

  Hmm. I found this which seems promising :

  http://sourceforge.net/projects/mjpg-streamer/

  ---

  Ok. I will try to explain what I am trying to do clearly and in much detail.

  I have a small humanoid robot with camera and wifi stick (this is the robot). The robot’s wifi stick average wifi transfer rate is 1769KB/s. The robot has 500Mhz CPU and 256MB RAM so it is not enough for any serious computations (moreover there are already couple modules running on the robot for motion, vision, sonar, speech etc).

  I have a PC from which I control the robot. I am trying to have the robot walk around the room and see a live stream video of what the robot sees in the PC.

  What I already have working. The robot is walking as I want him to do and taking images with the camera. The images are being sent through UDP protocol to the PC where I am receiving them (I have verified this by saving the incoming images on the disk).

  The camera returns images which are 640 x 480 px in YUV442 colorspace. I am sending the images with lossy compression (JPEG) because I am trying to get the best possible FPS on the PC. I am doing the compression to JPEG on the robot with PIL library.

  My questions :

  1. Could somebody please give me some ideas about how to convert the incoming JPEG images to a live video stream ? I understand that I will need some video encoder for that. Which video encoder do you recommend ? FFMPEG or something else ? I am very new to video streaming so I want to know what is best for this task. I’d prefer to use Python to write this so I would prefer some video encoder or library which has Python API. But I guess if the library has some good command line API it doesn’t have to be in Python.

  2. What is the best FPS I could get out from this ? Given the 1769KB/s average wifi transfer rate and the dimensions of the images ? Should I use different compression than JPEG ?

  3. I will be happy to see any code examples. Links to articles explaining how to do this would be fine, too.

  Some code samples. Here is how I am sending JPEG images from robot to the PC (shortened simplified snippet). This runs on the robot :

  # lots of code here
  
  
  
  UDPSock = socket(AF_INET,SOCK_DGRAM)
  
  
  
    while 1:
  
      image = camProxy.getImageLocal(nameId)
  
      size = (image[0], image[1])
  
      data = image[6]
  
      im = Image.fromstring("YCbCr", size, data)
  
      s = StringIO.StringIO()
  
      im.save(s, "JPEG")
  
  
  
      UDPSock.sendto(s.getvalue(), addr)
  
  
  
      camProxy.releaseImage(nameId)
  
  
  
    UDPSock.close()
  
  
  
    # lots of code here

  Here is how I am receiving the images on the PC. This runs on the PC :

    # lots of code here
  
  
  
    UDPSock = socket(AF_INET,SOCK_DGRAM)
  
    UDPSock.bind(addr)
  
  
  
    while 1:
  
      data, addr = UDPSock.recvfrom(buf)
  
      # here I need to create a stream from the data
  
      # which contains JPEG image
  
  
  
    UDPSock.close()
  
  
  
    # lots of code here

• How to print AVFrame->pts in the 00:00:00.033 format ?

  16 janvier 2018, par siods333333

  I need to convert AVFrame->pts into the "00:00:00.033" formatted string, how should I do this ? It is in the AVStream->time_base scale, instead of the ffmpeg standard 1,000,000 scale, need to convert that too.

  I need to walk+decode the entire file, just to get keyframes and duration. Will pass them to ffmpeg filters after that.

  Should the first keyframe have timecode "00:00:00.000" or "00:00:00.033" ? Avidemux uses the latter, don’t know about the ffmpeg.

  I want to know if duration should be the pts of the last frame, or pts of the last frame plus one ?