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• Adobe connect video : FLV to MP4 (export, convert)

  4 mai 2022, par Guillaume Chevalier

  I would like to convert an adobe connect video from .flv in the downloaded zip to .mp4. I have already done the steps explained in this question and answer, however I get .flv files organised like this inside the .zip :

  



  

  



  Moreover, I know that ffmpeg can merge video and sound files together as well as concatenating resulting clips directly from the command-line which could be quite useful : https://www.labnol.org/internet/useful-ffmpeg-commands/28490/

  



  I can't ask the owner of the video to make it available as an .mp4 from within the adobe connect admin interface. Briefly, I would like to listen to those videos in x2 speed in VLC (just like what I do when listening to random math classes on YouTube - I put ON the x2 speed). The amount of time I would gain to watch adobe connect videos in x2 speed is MASSIVE.

  



  I think I am not the only one that would like to do this. There are a lot of questions on forums about downloading adobe connect videos, but the .flv format mixed with some .xml is generally a killer when the host does not make the videos properly available in .mp4.

  



  Dealing with the order of the .flv files is a puzzle. At least, I would not care to flush the chat away and leave some details like that behind, that would help to reconstruct the videos. Any scripts to automate the process would be useful.

  


• Low latency video shared in local gigabit network using linux [on hold]

  6 mai 2017, par user3387542

  For a robotics task we need to share the video (Webcam) live to about 6 or 7 users in the same room. OpenCV will be used on the clients to read the situation and send new tasks to the robots. Latency should not be much more than one second, the lower the better. What commands would you recommend for this ?

  We have one camera on a Linux host which wants to share the video to about 6 other units just some meters away.

  I already experimented with different setups. While raw-video looks like perfectly latency free (local loopback, the issue is the amount of data), any compression suddenly ads about a second delay.
  And how should we share this in the network. Is broadcasting the right approach ? How can it be so hard, they are right next to each other.

  Works locally, issues over the network.

  #server
  
  ffmpeg -f video4linux2 -r 10 -s 1280x720 -i /dev/video0 -c:v libx264 -preset veryfast -tune zerolatency -pix_fmt yuv420p -f mpegts - | socat - udp-sendto:192.168.0.255:12345,broadcast
  
  #client
  
  socat -u udp-recv:12345,reuseaddr - | vlc --live-caching=0 --network-caching=0 --file-caching=0 -

  raw video - perfectly fine like this, video with many artefacts if sent over the network

  ffmpeg -f video4linux2 -r 10 -s 1280x720 -i /dev/video0 -c:v rawvideo -f rawvideo -pix_fmt yuv420p - | vlc --demux rawvideo --rawvid-fps 10 --rawvid-width 1280 --rawvid-height 720 --rawvid-chroma I420 -

  The technology used doesen’t matter, we do not care about network load either. Just want to use opencv on different clients using live data.

• How does ffmpeg read stdin pipe ?

  17 novembre 2017, par ciclopez

  I’m working on a Python script that generates an image sequence based on user real time remote interaction, and uses ffmpeg to compress and stream this image sequence over the network for the user to watch it.
  As soon as an image is generated the script writes it to ffmpeg’s stdin and this action is repeated inside a loop to form a video.

  I was wondering what happens when ffmpeg is busy processing the previous image when I write to stdin.

  • Does the .stdin.write() command block execution until ffmpeg finishes processing the previous image ? (Consequence of the pipe buffer filling up)
  • What’s the buffer size of subprocess.PIPE ?
  • Is it editable ?
  • Is it possible to overwrite this buffer if it’s full, instead of blocking execution ?
  • Does ffmpeg continually read it’s input in a parallel process and buffers it until it’s free to take care of it ?
  • If that’s the case, what’s the size of ffmpeg’s input buffer and how can I change it ?

  I’m asking this because I want to fully understand how the data travels between Python and ffmpeg to reduce the latency to its minimum.

  Here is the part of the code I’m using to start ffmpeg :

  cmd = ['ffmpeg',
  
      '-f', 'rawvideo',
  
      '-s', '%dx%d'%(width, height),
  
      '-pix_fmt', 'rgba',
  
      '-r', '%d'%fps,
  
      '-i', '-',
  
      '-an',
  
      '-vcodec', 'libx264',
  
      '-tune', 'zerolatency',
  
      '-preset', 'ultrafast',
  
      '-bf', '0',
  
      '-f', 'mpegts',
  
      'udp://xxx.xxx.xxx.xxx:xxxxx']
  
  
  
  proc = subprocess.Popen(cmd, stdin=subprocess.PIPE)

  And this is what I call inside a loop when I want to pass an image to ffmpeg :

  proc.stdin.write(image)