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• How to extract frames in real time from the MediaStream object returned from the frontend in backend

  23 mai 2023, par Darwin Swartz

  is it possible to extract frames in real-time on the backend from a MediaStream object returned from the frontend ? something like :- instead of extracting frames from a canvas element in frontend and sending those frames to the backend in real time, can we send just the stream instance to the backend and extract frames there in real time until the user stops the recording ?

  


  chrome.tabCapture.capture({ audio: false, video: true }, function(stream) {
  // Use the media stream object here
});


  


  I am using tabCapture api which returns a stream, now I want to send this MediaStream instance in real time to the backend and extract frames there and edit something on them in real-time using OpenCV or FFmpeg. is this something technically possible ?

  


  One approach I have seen is

  


  chrome.tabCapture.capture({ audio: false, video: true }, function(stream) {
  video.srcObject = stream
  const canvas = document.createElement('canvas');
  const ctx = canvas.getContext('2d');
   ctx.drawImage(video, 0, 0, canvas.width, canvas.height);
  const imageData = canvas.toDataURL('image/jpeg');
});


  


  drawing each frame on top of a canvas and capturing those frames from it (in the frontend itself)and sending those frames in real-time to the backend using web sockets. I am not sure about this approach as this might be bad for frontend memory wise,

  


  What could be a more efficient way of implementing real-time frame editing with frame manipulation libraries like OpenCV and FFmpeg

  


• ffmpeg ouput the time with scan the black screen in the vdeo file

  23 décembre 2023, par jack

  I use the below command to detect the black screen in the video, but it can't output

  


  the time field with detected. May I know does have any command can let ffmpeg

  


  output the time in the detected ?

  


  ffmpeg -i "inputfile.mkv" -vf "blackdetect=d=2:pix_th=0.00" -an -f null -


  


  output :

  


  [blackdetect @ 0000024d543c41c0] black_start:876.009 black_end:878.011 black_duration:2.002

[blackdetect @ 0000024d543c41c0] black_start:893.026 black_end:895.028 black_duration:2.002


  


  I checked the below of ffmpeg website

  


  https://ffmpeg.org/ffmpeg-filters.html


  


  , but still can't understand it and need help.

  


• How to get time stamp of closet k-frame before a given timestamp with ffmpeg ?

  20 février 2013, par jAckOdE

  I want a ffmpeg seeking command that fast and accurate. I found this

  The solution is that we apply -ss for both input (fast seeking) and output (accurate seeking). The question is that if the input seeking is not accurate how can we be sure that the seeking position is accurate.

  For example : as the example used in the link, if we want to seek to 00:03:00, the command is something likes

  ffmpeg -ss 00:02:30 -i ... -ss 00:00:30
  As said, the first seeking will seek to somewhere else not 00:02:30, say 00:02:31. and after applying second seek, the final result would be 00:03:01- NOT what we want. Is that correct ?

  Where does fist seeking seek to ? Does it seek to k-frame that closet to 00:02:30 ?

  If so, here is my thought, correct me if i'm wrong : after first seeking, we get the timestamp of the result (in this example : 00:02:31), then we apply second seeking with appropriate time, in this case 00:00:29.

  Question is how do we get time stamp of first seeking's result ?