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• FFmpeg how to get the first drawtext's x,y value to the second drawtext, and change the fontsize every frame, how to create a var ?

  22 octobre 2019, par FFmpeg2019

  I have a ffmpeg code :

  ffmpeg -i input.mp4 -vf drawtext=text=hello:fontsize=18:x=rand(0,640):y=rand(0,480),drawtext=world:fontsize=fontsize+0.1:x=16+?:y=? output.mp4

  And have three questions :

  1. How to let the "fontsize+0.1" work ?
  2. The two " ?" how to get the first drawtext’s x,y values ? let the two strings become one string like this : hello world.
  3. how to create a var ?

• OpenCV returns an Array of All Zeros on video.read

  19 janvier 2020, par Ikechukwu Anude

  Below is the relevant code

  import cv2 as cv
  
  import numpy as np
  
  
  
  video = cv.VideoCapture(0) #tells obj to use built in camera\
  
  
  
  #create a face cascade object 
  
  face_cascade  = 
  
  cv.CascadeClassifier(r"C:\Users\xxxxxxx\AppData\Roaming\Python\Python36\site- 
  
  packages\cv2\data\haarcascade_frontalcatface.xml")
  
  
  
  a = 1
  
  #create loop to display a video
  
  while True:
  
      a = a + 1
  
      check, frame = video.read()
  
      print(frame)
  
  
  
      #converts to a gray scale img
  
      gray = cv.cvtColor(frame, cv.COLOR_BGR2GRAY)
  
  
  
      #create the faces
  
      faces = face_cascade.detectMultiScale(gray, scaleFactor=1.5, minNeighbors=5)
  
  
  
      for(x, y, w, h) in faces:
  
          print(x, y, w, h)
  
  
  
      #show the image
  
      cv.imshow('capturing', gray)
  
  
  
      key = cv.waitKey(1) #gen a new frame every 1ms
  
  
  
      if key == ord('q'): #once you enter 'q' the loop will be exited
  
          break
  
  
  
  print(a) #this will print the number of frames
  
  
  
  #captures the first frame
  
  video.release() #end the web cam
  
  
  
  #destroys the windows when you are not defined
  
  cv.destroyAllWindows()

  The code displays a video captured from my webcam camera. Despite that, OpevCV doesn’t seem to be processing any frames as all the frames look like this

   [[0 0 0]
  
    [0 0 0]
  
    [0 0 0]
  
    ...
  
    [0 0 0]
  
    [0 0 0]
  
    [0 0 0]]]

  which I assume means that they are empty.

  This I believe is preventing the algorithm from being able to detect my face in the frame. I have a feeling that the issue lies in the ffmpeg codec, but I’m not entirely sure how to proceed even if that is the case.

  OS : Windows 10
  Language : Python

  EDIT : The Frame is not empty but all the values in the array seem to be ’0’

  Why is the frame empty and how can I get OpenCV to detect my face in the frame ?

• Parsing x264 to LibAV in C

  26 mai 2018, par Stephan Pich

  For a Project in School I have to encode and mux a Yuv File to mp4 using the Libav and lib x264 explicitly. I’ve already managed to encode the File to h264 using the libx264 but now i’m stuck muxing them into mp4.

  I know that I’ve to write the NALU Packages into the file but I’ve no Idea how to turn the NALU to AVFrame or AVPacket.

  Thanks for your help in advance.