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• How can I get the final size after transcripting a video to stream it with fluent-ffmpeg ?

  5 avril 2018, par G. Manukyan

  I am trying to stream a video using createReadStream and using pipe(res) in node.js and it works fine if the file doesn’t need transcoding (mp4, webm).

  With mkv files I am using fluent-ffmpeg to transcode it on the fly, but the problem is that I can’t go back and forward in the html video player.

  download = function(file, req, res) {   
  
  
  
      const range = req.headers.range
  
      const parts = range.replace(/bytes=/, "").split("-")
  
  
  
      const start = parseInt(parts[0], 10);
  
      const end = parts[1] ? parseInt(parts[1], 10) : file.length - 1
  
  
  
      res.setHeader('Content-Type', 'video/webm')
  
      res.setHeader('Accept-Ranges', 'bytes');
  
      res.setHeader('Content-Length', 1 + end - start);
  
      res.setHeader('Content-Range', `bytes ${start}-${end}/${file.length}`);
  
      res.statusCode = 206;
  
  
  
      var stream = file.createReadStream({start, end})
  
  
  
      ffmpeg(stream)
  
      .videoCodec('libvpx')
  
      .audioCodec('libvorbis')
  
      .videoBitrate('512k')
  
      .format('webm')
  
      .on('start', () => {
  
          console.log('transcoding...')
  
      })
  
      .on('error', (err, stdout, stderr) => {
  
          console.log(err.message, err, stderr);
  
      })
  
      .on('progress', function(progress) {
  
          console.log(progress);
  
      })
  
      .on('end', function(filenames) {
  
          console.log("Finished transcoding.");           
  
      })
  
      .pipe(res);
  
  
  
  }

  I think that comes from the fact that we don’t know in advance the size of the final transcoded file so the range we send in the headers is wrong and somehow make the video player "limited".

  What can be a workaround to this problem ?

• Not able to run the final step of running supervisord for plumi

  1er avril 2021, par manic_startup

  on the github page https://github.com/plumi/plumi.app
I am on the final step of Step 6. see below section

  


  =========================

  


  Step 6 : start supervisord
With plumi buildout having finished and ffmpeg installed on our system, it's time to run supervisord :

  


  root@user :/home/plumi.app# ./bin/supervisord

  


  ========================

  


  When I type in the above on CentOS 7 it says "bash : ./bin/supervisord : No such file or directory

  


  I had to change some things in step 5 "Step 5 Install ffmpeg" for the centos section there are two urls in that section pointing to some repos. They did not work so I had to find some other ones on the Internet. The ones I used where.
https://dl.fedoraproject.org/pub/epel/7/x86_64/Packages/e/epel-release-7-13.noarch.rpm

  


  http://ftp.riken.jp/Linux/atrpms/el7-x86_64/atrpms/stable/atrpms-repo-7-7.el7.x86_64.rpm

  


  The first one looks the same but it is different also the only release available was 7-13 so i used that.
The second one is a different url but the file is the same.

  


  also in that section is asks to edit /etc/yum.repos.d/atrpms.repo. It asks to change the base URL to a URL similar to the what is asks when it asked to download from the second repo above. Obviously that url is different now so I changed it to this instead.
http://ftp.riken.jp/Linux/atrpms/el$releasever-$basearch/atrpms/stable/

  


  After this I asks to install ffmpeg this did not work so I used the below guide
https://linuxize.com/post/how-to-install-ffmpeg-on-centos-7/

  


  Then came the section 6 to install supervisord as explained at the start this did not work. Now im stuck !

  


  I have also realised that when I get to the following command in step 4.

  


  ./bin/python bootstrap.py && ./bin/buildout -v

  


  It fails and says "Error : couldn't find distribution for 'hachoir-parser==1.3.4' and bombs out. I have tried to find this file but cant install it and dont know if i even have the correct file. not sure what to do.

  


• When compressing a set of images with libx264, why does frame rate affect final output size ?

  3 avril 2018, par jd20

  I’m using ffmpeg to encode a set of images as a short timelapse video, using libx264 codec. My first attempt, I encoded it at 30 FPS, using :

  ffmpeg -r 30 -pattern_type glob -i "*.jpg" -vcodec libx264 -crf 30 -pix_fmt yuv420p output.mp4

  With 60 frames, that gives me a 163 KB file that’s 2 seconds long. Then I realized I needed it to be slower, so I re-ran the same command, but changed -r to 2. Now I have a file that’s 30 seconds long, but the size jumped to 891 KB ! The video quality looks perceptually the same.

  How do I encode at a slower frame rate, without the final file size ballooning ?

  ---

  Notes : Some theories I had, and things I checked. First, to make sure ffmpeg wasn’t duplicating frames in the longer verison, I check the I/P/B counts. The 30 FPS file had :

  [libx264 @ 0x7f9b26001c00] frame I:1     Avg QP:30.67  size: 44649
  
  [libx264 @ 0x7f9b26001c00] frame P:15    Avg QP:31.19  size:  5471
  
  [libx264 @ 0x7f9b26001c00] frame B:44    Avg QP:31.45  size:   767

  The 2 FPS file had :

  [libx264 @ 0x7fcd32842200] frame I:1     Avg QP:21.29  size: 90138
  
  [libx264 @ 0x7fcd32842200] frame P:15    Avg QP:22.48  size: 33686
  
  [libx264 @ 0x7fcd32842200] frame B:44    Avg QP:26.29  size:  6674

  So, the I/P/B counts are identical, but the QP is much lower for the 2 FPS file. To offset, I tried increasing -crf for the 2 FPS file, to get about the same target size, but that just gave me a very blurry video (had to go to crf=40). I tried messing with -minrate, -maxrate, -bt, none helped. I’m guessing there is some x264 codec setting which is frame rate dependent, but I’m at a loss trying to figure out which one (from what I understand, constant bitrate is affected by frame rate but CRF should not be, but maybe I’m misunderstanding it.