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• Dynamic video resolution

  4 janvier 2019, par Chen Yang

  I use ffmpeg to encode my mobile phone’s screenshot to a video. when my phone is vertical the screenshot’s resolution is 478 * 850.When horizontal the resolution is 850 * 478. Encoder could handle these image to encoded video frame, and i could play this video by ffplay correctly, i means if resolution change from 478 * 850 => 850 * 478 and it still could display full phone screen.
  But if i play this video with any other players, it only could play harf of phone screen when frame resolution change from 478 * 850 => 850 => 478.
  
  Do you guys know any video format could handle this situation？

• Promise chaining and resolution

  23 janvier 2019, par Shourya Sharma

  I am trying to convert videos one by one with the help of promises. i am using ffmpeg for conversion and multer for uploading multiple files.

  multer uploads multiple files at once after which i have to chain the conversions one by one. as of now it just converts the 1st file.

  i thought chaining of promises ..like in an array should work but i am confused if i can define new promises in an array as ffmpeg also returns a promise

  My router :

  const router = require('express').Router();
  
  const multer = require('multer');
  
  const ffmpeg = require('ffmpeg');
  
  
  
  let str;
  
  const storage = multer.diskStorage({
  
    destination: (req, file, cb) => {
  
      cb(null, './uploads');
  
    },
  
    filename: (req, file, cb) => {
  
      str = file.originalname.replace(/\.[^/.]+$/, "");
  
      str = str.replace(/[^a-z0-9+]+/gi, '_') + '.' + file.originalname.replace(/^.*\./, '');
  
      cb(null, str);
  
    }
  
  });
  
  
  
  const upload = multer({ storage: storage }).array('files', 12);
  
  
  
  router.post('/upload', (req, res, next) => {
  
    // req.files is an array of files
  
    // req.body will contain the text fields, if there were any
  
    function uploadFile() {
  
      return new Promise((resolve, reject) => {
  
        upload(req, res, (err) => {
  
          if (err) {
  
            res.send(err) // Pass errors to Express.
  
            reject(`Error: Something went wrong!`);
  
          } else if (req.files == undefined) {
  
            res.send(`No File selected.`);
  
            resolve();
  
          } else if (!err && req.files.length > 0) {
  
            res.status(201).send(`${req.files.length} File(s): ${req.files} uploaded successfully.`);
  
            console.log('uploaded');
  
            resolve();
  
          }
  
        });
  
      });
  
    }
  
  
  
    uploadFile().then(() => {
  
      try {
  
        var process = new ffmpeg('./uploads/' + str);
  
        process.then(function (video) {
  
          console.log('The video is ready to be processed');
  
          video.addCommand('-hide_banner', '');
  
          video.addCommand('-y', '');
  
          video.addCommand('-c:a', 'aac');
  
          video.addCommand('-ar', '48000');
  
          video.addCommand('-c:v', 'h264');
  
          video.addCommand('-profile:v', 'main');
  
          video.addCommand('-crf', '20');
  
          video.addCommand('-sc_threshold', '0');
  
          video.addCommand('-g', '50');
  
          video.addCommand('-keyint_min', '50');
  
          video.addCommand('-hls_time', '4');
  
          video.addCommand('-hls_playlist_type', 'vod');
  
          video.addCommand('-vf', 'scale=-2:720');
  
          video.addCommand('-b:v', '1400k');
  
          video.addCommand('-maxrate', '1498k');
  
          video.addCommand('-bufsize', '2100k');
  
          video.addCommand('-b:a', '128k');
  
          video.save('./converted/' + str, function (error, file) {
  
            if (!error)
  
              console.log('Video file: ' + file);
  
          });
  
          }, function (err) {
  
            console.log('Error: ' + err);
  
          });
  
      } catch (e) {
  
        console.log(e.code);
  
        console.log(e.msg);
  
      }
  
    }).catch((err) => {
  
      console.log(Error, err);
  
    });
  
  });
  
  
  
  module.exports = router;

• poor resolution in video out put from ffmpeg

  27 janvier 2019, par Clinton Winant

  I make animation of png or jpg frames output from a fluid flow simulation code. An example image looks like :
  

  The ffmpeg command I use is

  ffmpeg  -f image2 -r 20 -i img%04d.png -vcodec mpeg4 animate.avi

  The resulting video is very poor as can be seen in the screen capture of a single frame of the output file animate.avi :

  

  There are elongated shaded areas on either side of the yellow streaks, and the ffmpeg produced frame is much grainier than the original .png.

  I understand that there has to be massive compression in the production of the video, and I assume the problem lies there, where the compression id poor for the kind of images I am trying to animate. How could I use ffmpeg to produce a video with quality comparable to the original images I have ?

  PS I am using Debian Buster, the png images have a resolution of 100 dpi.