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• Stream copy given start and end time in ffmpeg

  10 mai 2013, par praks411

  I'm trying a small program which cuts clip from video file given start and end time. For this I'm doing a simple stream copy of both audio and video stream. I just copied the pts and dts from input packet to output with proper re-scaling. However the output which I'm getting is blank for some duration and then only for last few seconds it is displayed. I thought this could to problem of incorrent pts and dts. So I just manually set pts and dts using counter for each stream. Though I'm able to get the clip but video is very fast and audio goes fine. Please someone explain me how to set current pts and dts for both audio and video stream, when doing stream copy.

  Thanks
  Pradeep

• 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 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