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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 ?

• doc/decoders,decoders : add various missing final dots

  21 juin 2013, par Stefano Sabatini

  doc/decoders,decoders : add various missing final dots
  Enhance consistency.
  

  • [DH] doc/decoders.texi
  • [DH] doc/encoders.texi