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• saving frames from webcam stream

  30 décembre 2018, par Alex Witsil

  I would like a routine that systematically extracts and saves the frames from webcam footage to a local directory on my personal computer.

  Specifically, I am trying to save frames from the webcam at Old Faithful geyser in Yellowstone Natl. Park. (https://www.nps.gov/yell/customcf/geyser_webcam_updated.htm)

  Ideally, I would like to :

  1. be able to control the rate at which frames are downloaded (e.g. take 1 frame every minute)
  2. use FFMPEG or R
  3. Save the actual frame and not a snapshot of the webpage

  Despite point 3 above, I’ve tried simply taking a screenshot in R using the package webshot :

  library(webshot)
  
  i=1
  
  while(i<=2) { 
  
  webshot('https://www.nps.gov/yell/customcf/geyser_webcam_updated.htm',delay=60,paste(i,'.png',sep=""))
  
  
  
  i=i+1
  
  }

  However, from the above code I get these two images :

  
  
  Despite the delay in the webshot() function (60 seconds) the two images are the same not to mention the obvious play button in the middle. This method also seems a bit of a hack as it is saving a snapshot of the website and not the frames themselves.

  I am certainly open to to using more appropriate command line tools (I am just unsure of what they are). Any help is greatly appreciated !

• Download a youtube video without storing it on the server

  6 mai 2019, par Baraque Obahamas

  I have a personal php script that allows me to download the videos of my choice. Currently, this runs youtube-dl and if necessary convert the video, ffmpeg then.

  I’m looking for a way to allow my script to download/convert the video without even storing it on the server. Make sure that youtube-dl/ffmpeg acts as a gateway but without downloading the file.

  Do you have any idea how to do this ? The idea would be to run ffmpeg on the youtube link and not on the video after it has been downloaded, and allow the user to download it at the same time as the conversion is in progress.

  We can see that this site for example www.onlinevideoconverter.com uses this method, because if we ask for a video of 2 hours or more, it allows us to download it immediately.

• Advice on how to specify length of animated GPX video with ffmpeg/image2pipe

  21 mai 2019, par Chris Olin

  I’m working on a personal project involving an action camera that records GPS data alongside video from an image sensor. I found an open source projected on GitHub called ’trackanimation’ that uses a colored marker to trace the GPX path on a OpenStreetMaps overlay, but it appears that the project has been abandoned. I’m trying to sync the trackanimation video to the image sensor video, but when I try using video editing software to slow the GPX video down to 1%, it still ends up being shorter than the image sensor video. I’ve tried messing with the baked in ffmpeg command in make_video(), but still can’t get the output video to be as long as I want it to be.

  I started digging into the library source to see how the video was being created, tried tweaking a couple things to no avail.

  import trackanimation
  
  from trackanimation.animation import AnimationTrack
  
  
  
  gpx_file = "Videos/20190516 unity ride #2.mp4.gpx"
  
  gpx_track = trackanimation.read_track(gpx_file)
  
  
  
  fig = AnimationTrack(df_points=gpx_track, dpi=300, bg_map=True, map_transparency=0.7)
  
  fig.make_video(output_file="Videos/1-11trackanimationtest.mp4", framerate=30, linewidth=1.0)

      def make_video(self, linewidth=0.5, output_file='video', framerate=5):
  
          cmdstring = ('ffmpeg',
  
                       '-y',
  
                       '-loglevel', 'quiet',
  
                       '-framerate', str(framerate),
  
                       '-f', 'image2pipe',
  
                       '-i', 'pipe:',
  
                       '-r', '25',
  
                       '-s', '1920x1080',
  
                       '-pix_fmt', 'yuv420p',
  
                       output_file + '.mp4'
  
                       )

  I expect that I should be able to linearly "slow" the GPX video to a dynamic value based on the length of the video and the length I want it to be.