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• How to change mjpeg to yuyv422 from a webcam to a v4l2loopback ?

  3 janvier 2020, par Dev Null

  Backstory : One livestreaming site I use isn’t smart enough to detect the capabilities of my webcam (Logitech Brio, 4k), and instead just uses the default frames per second settings, which is 5fps.

  (full solution walk-through in the answer)

  The best solution I could think of (besides changing livestream providers) was to create a loopback virtual webcam using v4l2loopback that I could force to have the exact settings I wanted to use on that livestream site.

  For the brio, the higher frame rates come with mjpeg, not the default yuyv.

  Problem 1 :

  I could easily read mjpeg, but unfortunately kept banging my head against the wall because v4l2loopback evidently only wanted yuyv.

  I tried things like :

  ffmpeg -f v4l2              \
  
         -input_format mjpeg  \
  
         -framerate 30        \
  
         -video_size 1280x720 \
  
         -i /dev/video0       \
  
         -vcodec copy         \
  
         -f v4l2 /dev/video6

  and

  ffmpeg -f v4l2              \
  
         -input_format mjpeg  \
  
         -framerate 30        \
  
         -video_size 1280x720 \
  
         -i /dev/video0       \
  
         -vcodec yuyv422      \ # this line changed (even tried "copy")
  
         -f v4l2 /dev/video6

  But they wouldn’t work. I got errors like :

  Unknown V4L2 pixel format equivalent for yuvj422p

  and

  ...deprecated pixel format used, make sure you did set range correctly...

  ...V4L2 output device supports only a single raw video stream...

  Eventually I got this to work :

  ffmpeg -f v4l2              \
  
         -input_format mjpeg  \
  
         -framerate 30        \
  
         -video_size 1280x720 \
  
         -i /dev/video0       \
  
         -pix_fmt yuyv422     \ # The winning entry
  
         -f v4l2 /dev/video6

  Problem 2

  The next problem was getting chrome to see the virtual webcam. It worked correctly with guvcview, and on firefox I could use webcam testing sites and it would pick the virtual camera up without a problem.

  Turns out google, in it’s overly-protective nature (while it’s siphoning off all our data, btw), doesn’t want to use webcams that can be read and written to.

  So when starting v4l2loopback you have to tell it to announce that it’s "read only" to consumers like chrome.

  Here’s the exact modprobe I use that works :

  sudo modprobe v4l2loopback devices=1 exclusive_caps=1

• Last subprocess call not working in concatenation code with FFMPEG. How should I go about fixing this ?

  28 novembre 2019, par S1mple

  clips = []
  
  
  
  #generates a list of mp4 files in a folder
  
  def clipFinder(CurrentDir, fileType):
  
      clips.clear()
  
      for r,d,f in os.walk(CurrentDir):
  
          for file in f:
  
              if fileType in file:
  
                  clips.append(r+file)
  
      random.shuffle(clips)
  
  
  
  #removes all files that have the string 'vod' in them as they cause problems during concatenation
  
  def removeVods(r):
  
      for f in clips:
  
          if 'vod' in clips:
  
              os.remove(r+f)
  
  
  
  #generates a string using the clips list to insert into the ffmpeg command
  
  def clipString():
  
      string = 'intermediate'
  
      clipList = []
  
      clipNum = 1
  
      for f in clips:
  
          clipList.append(string+str(clipNum)+'.ts'+'|')
  
          clipNum+=1
  
      string1 = ''.join(clipList)
  
      string2 = string1[0:len(string1)-1]
  
      return string2
  
  
  
  #concatenates the mp4 files in the clipString
  
  def concatFiles():
  
      clipFinder('***', '.mp4')
  
      removeVods('***')
  
      i = 0
  
      intermediates = []
  
      for f in clips:
  
          subprocess.call(['***', '-i', clips[i], '-c', 'copy', '-bsf:v', 'h264_mp4toannexb', '-f', 'mpegts', 'intermediate'+ str(i+1) +'.ts'])
  
          i += 1 
  
      clipsLength = len(clips)
  
      subprocess.call['***', '-i', '"concat:' + clipString() + '"', '-c', 'copy', '-bsf:a 
  
      aac_adtstoasc', 'output.mp4']

  I am trying to make a clip concatenator, but the last subprocess call won’t run and gives me no error. When I run the script the first FFmpeg call works fine and gives me my intermediate mp4 files, however, the second command, which works when I run it in terminal, does not work when I run it from python using subprocess.call.

  Problematic code :

  subprocess.call(['***', '-i', '"concat:' + clipString() + '"', '-c', 'copy', '-bsf:a aac_adtstoasc', 'output.mp4'])

  all places with * were paths such as : /davidscomputer/bin/ffmpeg/

• TypeError : 'function' object is not subscriptable Python with ffmpeg

  25 novembre 2019, par S1mple

  clips = []
  
  
  
  def clipFinder(CurrentDir, fileType):
  
      clips.clear()
  
      for r,d,f in os.walk(CurrentDir):
  
          for file in f:
  
              if fileType in file:
  
                  clips.append(r+file)
  
      random.shuffle(clips)
  
  
  
  def removeVods(r):
  
      for f in clips:
  
          if 'vod' in clips:
  
              os.remove(r+f)
  
  
  
  def clipString():
  
      string = 'intermediate'
  
      clipList = []
  
      clipNum = 1
  
      for f in clips:
  
          clipList.append(string+str(clipNum)+'.ts'+'|')
  
          clipNum+=1
  
      string1 = ''.join(clipList)
  
      string2 = string1[0:len(string1)-1]
  
      return string2
  
  
  
  def concatFiles():
  
      clipFinder('***', '.mp4')
  
      removeVods('***')
  
      i = 0
  
      intermediates = []
  
      for f in clips:
  
          subprocess.call(['***', '-i', clips[i], '-c', 'copy', '-bsf:v', 'h264_mp4toannexb', '-f', 'mpegts', 'intermediate'+ str(i+1) +'.ts'])
  
          i += 1 
  
      clipsLength = len(clips)
  
      subprocess.call['***', '-i', '"concat:' + clipString() + '"', '-c', 'copy', '-bsf:a 
  
      aac_adtstoasc', 'output.mp4']

  I am trying to make a clip concatenator, but the last subprocess call won’t run and gives me the error shown in the question.

  Problematic code :

  subprocess.call(['***', '-i', '"concat:' + clipString() + '"', '-c', 'copy', '-bsf:a aac_adtstoasc', 'output.mp4'])

  all places with * were paths such as :
  /davidscomputer/bin/ffmpeg/