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• HTML 5 currentTime accuracy

  1er septembre 2015, par Daniel

  I’m working on a project where we are using the value from the video element’s currentTime property to perform processing on the server backend using ffmpeg. I’ve come across an issue where the video element seems to report a time code that is slightly different from the time code ffmpeg needs to access the correct point in the video.

  So for instance in Firefox if the currentTime property reports that the current video time is 26.83 I might find that the frame I really want ended at 26.72 and so if I use the time to extract a frame using ffmpeg on the server I get the next frame instead of the current frame.

  The amount of offset seems to be slightly different in different parts of the video and in different videos. But the offset is usually close to one tenth of a second in Firefox. In chrome the currentTime actually seems to be ahead or the correct currentTime by about 5 hundredths of a second. It’s more difficult to figure out the offset in IE because the place where the frame shifts seems to change as I enter different time codes to look for the exact time code where the frame changes.

  I’m pretty sure the time as used by ffmpeg is the correct time. It seems to agree more closely with other video editing software such as adobe premier.

  Any ideas on what could be causing this behavior ?

  JS to get currentTime :

  AVideo.prototype.getCurrentTime = function()
  
  {
  
     return this.videoElement[0].currentTime;
  
  };

  Resulting ffmpeg command :

  ffmpeg -y -i '/tmp/myVideo.mov' -vframes 1 -ss 2.4871 -f image2   -y '/tmp/myFrame.jpg' 2>&1

• How to use ffmpeg for streaming mp4 via websocket

  5 août 2015, par curtiss

  I’ve written a sample in nodejs wich streams some input to the client via websocket connection in mp4 format. On the client side, the mp4 packages ar added to a MediaSourceBuffer.

  This runs fine, but only if the client gets the stream from the beginning with the first package. So another client can’t play the current Stream, because he won’t get the Stream from the beginning.

  I tried (try&error) to save the first package ffmpeg sends and send this at the beginning of a new connection, then the current stream. Then the MediaSourceBuffer breaks because of encoding error..

  Here is the ffmpeg command :

  -i someInput -g 59 
  
  -vcodec libx264 -profile:v baseline 
  
  -f mp4 -movflags empty_moov+omit_tfhd_offset+frag_keyframe+default_base_moof
  
  -reset_timestamps 1
  
  -

  The part "empty_moov+omit_tfhd_offset+frag_keyframe+default_base_moof" should make the Streampackages independet in putting the moovatom at the beginning of each part and sizing the parts in 59 frames each by keyframe, so i dont get it why i cant view the Stream beginning after the start.

• FFMPEG script to merge all files in a list and make a 1920x1080p 60fps mp4 video

  28 février 2021, par BitBit

  I have a list of 46 videos in a text file. I tried the concat method to merge all of them, which worked but the quality is very poor and the audio is bugged/missing at parts.

  Can someone please help me with a script to merge all 46 videos and the output to be 1920x1080 60fps mp4 video ?