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• Is ffmpeg able to read ArrayBuffer input from stream

  7 juillet 2017, par jAndy

  I want to accomplish the following tasks :

  • Record Video+Audio from any HTML5 (MediaStream) capable browser
  • Send that data via WebSocket as Blob / ArrayBuffer chunks to a server
  • Broadcast that input stream-data to multiple clients

  As it turns out, this brought me into a world of pain. The first task is fairly simple using the HTML5 MediaStream objects alongside WebSockets.

  // ... for simplicity...
  
  navigator.mediaDevices.getUserMedia({ audio: true, video: true }).then(stream => {
  
      let mediaRecorder = new MediaRecorder( stream );
  
      // ...
  
      mediaRecorder.ondataavailable = e => {
  
          webSocket.send( 'newVideoData', e.data ); // configured for binary data
  
      };
  
  });

  Now, I want to receive those data fragments and stream those via nginx vod module, because I guess I want the output stream in HLS or DASH.
  I could write a little nodejs script as backend, which just receives the binary chunks and write them to a file or stream, and just reference it so nginx vod module could possibly read it and create the m3u8 manifest on the fly ?

  I am wondering now,

  • if ffmpeg is able to read that binary data directly (should be webm format), without a man-in-the-middle script, "somehow" ?
  • If not, do I have to write the data down into a file and pass that as input to ffmpeg or can I (should I) pipe the data to a self spawned ffmpeg instance ? (if so, how ?)
  • Do I actually need the nginx server (probably alongside rtmp module) to deliver the output stream as HLS or could I just use ffmpeg to also create a dynamic manifest ?
  • Is the nginx vod module capable of creating a dynamic hls/dash manifest or must the input data be complete beforehand ?
  • Ultimately, am I on the totally wrong track here ? :P

  Actually I just want to create a little video-live-chat demo, without any plugins or 3rd party encoding software, pure browser.

• ffmpeg -ss then apply filter then concat producing timestamp errors

  6 août 2020, par Bob Ramsey

  Using ffmpeg, I have split a file into multiple parts using -ss. Then I apply a filter to some of the files, then concat the files back together. When I do that, I get : Non-monotonous DTS in output stream 0:0 ; previous : 341334, current : 340526 ; changing to 341335. This may result in incorrect timestamps in the output file. The output file plays, but there are noticeable skips where the files are joined.

  


  Here's how I am splitting the file :

  


  ffmpeg -i full_source.mp4 -ss 0 -to 14.264250 -c copy  01-plain.mp4
ffmpeg -i full_source.mp4 -ss 14.264250 -to 18.435083 -c copy  01-filtered.mp4

ffmpeg -i full_source.mp4 -ss 18.435083 -to 29.988292 -c copy  02-plain.mp4
ffmpeg -i full_source.mp4 -ss 29.988292 -to 31.865167 -c copy  02-filtered.mp4
...
ffmpeg -i full_source.mp4 -ss 0 -to 14.264250 -c copy  10-plain.mp4
ffmpeg -i full_source.mp4 -ss 234.484203 -to 300.000 -c copy  10-filtered.mp4


  


  Then I apply a different drawtext filter on each of the 10 filtered files and save them with a new name, like :

  


  ffmpeg -hide_banner -loglevel warning -y -i 01-filtered.mp4 -filter_complex "drawtext=fontfile=calibri.ttf:fontsize=24:fontcolor=white:x=300:y=500:text='hello world'" -crf 15 01-filtered-complete.mp4


  


  Finally, I join all of the plain and complete files back together like this :

  


  ffmpeg  -f concat -safe 0 -i mylist.txt -c:a copy -c:v copy  outfile.mp4


  


  And that's where the timing error comes in. I've tried adding -vsync drop in the concat command, but that didn't really work either. Same version of ffmpeg does the split, the filter, and the concat. I've tried different versions, everything from 20170519 to one from May 2020 with the same result. Always making sure that all three steps are done by the same version of ffmpeg.

  


  The only thing I can see is that ffprobe shows a duration of 14.27 for 01-plain.mp4 when it should be 14.264250. All of the other files show a similar rounding difference. The files are 23.98 fps. If I do all of my filters in really long command without splitting the file, I can use the more precise numbers with no problem. It just takes 10 times as long. This is all scripted, it happens a couple of hundred times a day and time is money, so I can't take 10 times as long to do each file.

  


  Any ideas ? Thanks in advance !

  


• DrawText and crossfade effect - ffmpeg

  22 juillet 2018, par Geek

  I have one video with crossfade effect and i want add text on this video (drawtext).
  However when i add a filter text, he remove a crossfade effect in the final video.

  Command to create video with crossfade effect :

  ffmpeg -i first.mp4 -i second.mp4 -filter_complex 
  
      "[0:v]trim=start=0:end=2,setpts=PTS-STARTPTS[0_clip_1];
  
      [0:v]trim=start=2:end=3,setpts=PTS-STARTPTS[fadeoutsrc_0];
  
      [fadeoutsrc_0]format=pix_fmts=yuva420p,fade=t=out:st=0:d=1:alpha=1[fadeout_0];
  
      [fadeout_0]fifo[fadeoutfifo_0];[1:v]trim=start=1,setpts=PTS-STARTPTS[1_clip_2];
  
      [1:v]trim=start=0:end=1,setpts=PTS-STARTPTS[fadeinsrc_1];
  
      [fadeinsrc_1]format=pix_fmts=yuva420p,fade=t=in:st=0:d=1:alpha=1[fadein_1];
  
      [fadein_1]fifo[fadeinfifo_1];
  
      [fadeoutfifo_0][fadeinfifo_1]overlay[crossfade_1];
  
      [0_clip_1][crossfade_1][1_clip_2]concat=n=3[output];[0:a][1:a] acrossfade=d=1 [audio]" 
  
  -map "[output]" -map "[audio]" videoWithCrossfade.mp4

  Command to add filter text :

  ffmpeg -i videoWithCrossfade.mp4 -filter_complex 
  
      "/Windows/fonts/arial.ttf':text='hello world!':fontcolor=white:fontsize=40:box=1:boxcolor=red
  
      @0.5:boxborderw=10:x=500:y=500"
  
      output.mp4

  this is the link of video : http://www.mediafire.com/file/kw3lvdb2rp1bs6u/videoWithCrossfade.mp4/file
  http://www.mediafire.com/file/iycdzozsqzosq87/output.mp4/file

  Thanks for your help !