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• Most efficient way to render bitmap to screen on Linux [on hold]

  22 juillet 2019, par Maximus

  My goal is to receive a video feed from wifi and display it on my screen. For this, I’ve created a couple of small programs and a bash script to automate them running. It works like this :

  UDPBitmap/Plotter & ffplay -i - < UDPBitmap/pipe & python requester.py;

  Translation : There is a C++ program called Plotter, its job is to receive packets on an assigned UDP port, process them and write it to pipe (named : UDPBitmap/pipe). The pipe is accessed by ffplay, and ffplay renders the video on screen. The python file is solely responsible for accessing and controlling the camera with various HTTP requests.

  The above command works fine, everything works as expected. However, the resulting latency and framerate is a bit lower than what I’ve wanted. The bottleneck of this program is not the pipe, it is fast enough. Wifi transmission is also fast enough. The only thing left is ffplay.

  Question :

  What is the most efficient way to render a bitmap to screen, on Linux ? Is there a de facto library for this that I can use ?

  Note :

  • Language/framework/library does not matter (C, C++, Java, Python, native linux tools and so on...)
  • I do not need a window handle, but is SDL+OpenGL the way to go ?
  • Writing directly to the framebuffer would be super cool...

• ffmpeg itsoffset doesnt apply offset to mp4

  26 juillet 2019, par brux

  The following command mixes an mp4 and an mp3 together, keeping the audio from the mp4.

  ffmpeg -i video.mp4 -i audio.mp3 -map 0:v -c:v copy -filter_complex '[0:a][1:a]amix[aout]' -map '[aout]' -shortest out.mp4

  The command works as expected.

  Now I want to offset the mp4 file (both the audio and video stream of the mp4) so that there is a delay of 500ms at the start of the mp4, here is my command :

  ffmpeg -itsoffset 00:00:00.500 -i video.mp4 -i audio.mp3 -map 0:v -c:v copy -filter_complex '[0:a][1:a]amix[aout]' -map '[aout]' -shortest out.mp4

  This doesnt work as expected, the output doesnt have the expected delay of 500ms at the start of the mp4 streams. It appears the output is just the same as the first command I ran.

  The version of ffmpeg I am using is :

  ffmpeg version n4.0-39-gda39990

  Here are the files I’m using :

  video.mp4

  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/storage/emulated/0/video.mp4':
  
        Metadata:
  
          major_brand     : mp42
  
          minor_version   : 0
  
          compatible_brands: isommp42
  
          creation_time   : 2019-07-26T03:28:49.000000Z
  
          com.android.version: 8.0.0
  
        Duration: 00:00:07.64, start: 0.000000, bitrate: 20534 kb/s
  
          Stream #0:0(eng): Video: h264 (avc1 / 0x31637661), yuvj420p(pc, smpte170m), 1920x1080, 20966 kb/s, SAR 1:1 DAR 16:9, 29.70 fps, 29.75 tbr, 90k tbn, 180k tbc (default)
  
          Metadata:
  
            rotate          : 270
  
            creation_time   : 2019-07-26T03:28:49.000000Z
  
            handler_name    : VideoHandle
  
          Side data:
  
            displaymatrix: rotation of 90.00 degrees
  
          Stream #0:1(eng): Audio: aac (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 96 kb/s (default)
  
          Metadata:
  
            creation_time   : 2019-07-26T03:28:49.000000Z
  
            handler_name    : SoundHandle

  audio.mp3

  Input #0, mp3, from '/storage/emulated/0/audio.mp3':
  
        Metadata:
  
          album           : Sunflower (Spider-Man: Into the Spider-Verse) - Single
  
          composer        : Louis Bell, Carter Lang, Austin Richard Post, Billy Walsh & Khalif Malik Ibin Shaman Brown
  
          genre           : Hip-Hop/Rap
  
          copyright       : This Compilation ℗ 2018 Republic Records, a division of UMG Recordings, Inc.
  
          title           : Sunflower (Spider-Man: Into the Spider-Verse)
  
          artist          : Post Malone & Swae Lee
  
          album_artist    : Post Malone & Swae Lee
  
          track           : 01/01
  
          TYER            : 2018-10-18T07:00:00Z
  
        Duration: 00:02:38.07, start: 0.000000, bitrate: 325 kb/s
  
          Stream #0:0: Audio: mp3, 44100 Hz, stereo, fltp, 320 kb/s
  
          Stream #0:1: Video: mjpeg, yuvj444p(pc, bt470bg/unknown/unknown), 1400x1400 [SAR 300:300 DAR 1:1], 90k tbr, 90k tbn, 90k tbc
  
          Metadata:
  
            comment         : Cover (front)

• How to use Python (For example, ffmpeg or moviePy) to split large video to display on multiple screen [on hold]

  27 juillet 2019, par Chen Clarence

  I am trying to find resources to split a very long (1080*15360) video into 8 1080p videos of the same time length. Is there anything that could achieve this, or even better allows control over each pixel（use a function to cover part of my video with a black circle）. Right now I have to brute force it, such as the following, but I’m sure there are much more efficient methods. Thanks in advance !

  cap=cv2.VideoCapture('sample.avi')
  
  #inputs & check for error
  
  numberOfScreens=8
  
  screenArrangement=(1,8)
  
  if (numberOfScreens!=(screenArrangement[0]*screenArrangement[1])):
  
      raise ValueError('The screen arrangement does not match the number of scrrens')
  
      exit(0)
  
  
  
  
  
  currentFrame=0
  
  originalFrames=[]
  
  while(True):
  
      #reading frames
  
      ret,frame=cap.read()
  
      if not ret:
  
          break
  
      height, width, layers = frame.shape
  
      unitHeight=(int)(height/screenArrangement[0])   #reduce this to outside loop
  
      unitWidth=(int)(width/screenArrangement[1])
  
      #cutting frames into desired size
  
      for i in range(screenArrangement[0]):
  
          for j in range(screenArrangement[1]):
  
              try:
  
                  if not os.path.exists('Screen'+str(i*screenArrangement[0]+j+1)):
  
                      os.makedirs('Screen'+str(i*screenArrangement[0]+j+1))
  
                      print('creating directory '+'Screen'+str(i*screenArrangement[0]+j+1))
  
              except OSError:
  
                  print ("Error Creating Directory")
  
              name='./Screen'+str(i*screenArrangement[0]+j+1)+'/frame'+str(currentFrame)+'.png'
  
              cropImg = frame[(i*unitHeight):((i+1)*unitHeight), (j*unitWidth):((j+1)*unitWidth)]
  
              print('creating'+name)
  
              #saving cropeed frames
  
              cv2.imwrite(name, cropImg,[cv2.IMWRITE_PNG_COMPRESSION, 0])
  
      currentFrame+=1
  
  Frames=currentFrame 
  
  
  
  #setting up the writer object
  
  fourcc = cv2.VideoWriter_fourcc(*'XVID')
  
  writer=cv2.VideoWriter('Screen1.avi', fourcc, 30, (unitWidth, unitHeight), True)
  
  #write the video
  
  for i in range(Frames):
  
      img=cv2.imread('./Screen1/frame'+str(i)+'.png')
  
      writer.write(img)
  
  writer.release()
  
  cap.release()
  
  cv2.destroyAllWindows()