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• How to calculate the "Range" header for mp4 file to play/download a part of it ? [youtube-dl]

  5 décembre 2016, par supersan

  I’m using youtube-dl to download videos from YouTube. Unfortunately, sometimes I just need to download a part of the video like 10 seconds of a 3 hour video and here is how I see I can do it.

  Step 1 : Get the URL of the mp4 file from youtube-dl.

  youtube-dl -g -f "[ext=mp4]" https://www.youtube.com/watch?v=qOZ1u9VpoMk

  This returns $url : the full URL of mp4 file on server.

  Step 2 : Download part of the video using curl

  curl -r $startBytes-$endBytes $url

  But how to calculate $startBytes and $endBytes. What is the formula for that ?

  P.S I was thinking could be something as simple but this isn’t it..

  $startBytes = (total_size_of_video / total_length_of_video_secs) * start_seconds

  P.P.S. When I play the mp4 video in Chrome and use the scrub bar to jump around in the video, Chrome too send the Range header to the same URL (as I can see in fiddler)

• cut a part from an mp4 video with no wreckage using ffmpeg and php

  19 janvier 2017, par NegroNero

  I use this cmd below to cut a part from an MP4 video :

  ffmpeg -ss 00:00:10.500 -i {$ffmpeg_mp4_vinput} -t 00:00:17.430 {$ffmpeg_mp4_voutput} 2>&1

  and

  ffmpeg -ss 00:00:10.500 -i {$ffmpeg_mp4_vinput} -to 00:00:17.430 {$ffmpeg_mp4_voutput} 2>&1

  and

  ffmpeg -ss 00:00:10.500 -i {$ffmpeg_mp4_vinput} -t 7 {$ffmpeg_mp4_voutput} 2>&1

  All those cmds are called by exec() php function, they all work fine with SAME result.

  Problem is when I cut a video with one of those commands, I get a video with long video from what I set in from-to in the commands. For example I get 1 second before and more than 2+ seconds after.

  Is there something missed out from the commands ?

• OpenCV : FFMPEG : tag 0xffffffff/'����' is not found (format 'mp4 / MP4 (MPEG-4 Part 14)')'

  2 mars 2017, par Gingerbread

  I am trying to save a background subtracted video in python and the following is my code.

  import cv2
  
  import numpy as np
  
  
  
  capture = cv2.VideoCapture('MAH00119.mp4')
  
  size = (int(capture.get(cv2.CAP_PROP_FRAME_WIDTH)),
  
  int(capture.get(cv2.CAP_PROP_FRAME_HEIGHT)))
  
  fourcc = cv2.VideoWriter_fourcc(*'X264')
  
  out = cv2.VideoWriter('output.mp4', -1 , 20.0 , size)
  
  fgbg= cv2.createBackgroundSubtractorMOG2()
  
  
  
  while True:
  
      ret, img = capture.read()
  
      if ret==True:
  
          fgmask = fgbg.apply(img)
  
          out.write(fgmask)
  
          cv2.imshow('img',fgmask)
  
  
  
      if(cv2.waitKey(27)!=-1):
  
          break
  
  
  
  capture.release()
  
  out.release()
  
  cv2.destroyAllWindows()

  However, this keeps throwing the following error : "OpenCV : FFMPEG : tag 0xffffffff/’����’ is not found (format ’mp4 / MP4 (MPEG-4 Part 14)’)’"

  I have FFMPEG installed and have added it to the environment variables. My background subtraction code without having to save to a file works fine, so I know there’s nothing wrong with openCV installation. I am stuck at this place. I know that my python doesn’t seem to recognize FFMPEG but I don’t know what else to do apart from adding FFMPEG to the environment variables.
  I am using OpenCV version 3.2 on Windows 10 and Python 2.7.

  Any help will be much appreciated !