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• Streaming images as video on the fly using ffmpeg and ffserver

  1er décembre 2017, par AstrOne

  I have an OpenGL application that renders a 3D scene, and in every frame, it captures the OpenGL frame buffer, and saves it to a series of files (frame_1.png, frame_2.png, etc). I want to convert those images into a video stream and serve/broadcast it. From what I have read so far one solution would be to use ffmpeg and ffserver.

  There are several similar questions on StackOverflow but each one is a bit different, and they don’t ask exactly what I want. For example there are solutions to generate videos (but not streams) from images. Some others generate streams but not "live" ones. And so on.

  • I want the generated frames to be streamed as soon as possible after they are created. This is because the OpenGL application is supposed to be interactive. Latter on, a remote user should be able to send events (mouse motions and clicks) and interact with the rendered 3D scene.
  • I don’t want ffserver to do any kind of buffering because there is nothing to buffer, the frames must be served immediately.
  • Given that the frames must be served immediately, I guess I could just write the frames on top of each other. However, in that case there will be a synchronisation problem because the ffmpeg may try to read the image before the OpenGL application has finished writing on it. Any thoughts on that ?
  • In case the ffserver and the OpenGL application share the same RAM and not just the filesystem, ideally, I would like to not use files at all for the communication. I guess for my OpenGL application I could use something like mmap or some sort of shared memory, but ffmpeg can’t read from some kind of shared memory, right ?

  I would be more than grateful if someone could advice me how I need to setup the ffserver and the ffmpeg command to meet the above requirements (especially the first one).

• Using FFMPEG to overlay 2 concat-demux videos

  10 juin 2021, par marco

  I am making a screen recording software that captures gestures/mouse moves as coordinates+timestamps, and would like to overlay those on the screen recording. I have a folder of "Frames" that have a red circle and the rest transparent that correspond to the gestures.

  


  The way I initially got it working was to use concat-demux to generate a video of the gestures, and then I overlay it with ffmpeg by chromakeying out the black background and overlaying it, but that is very slow.

  


  Is there a better/faster way to do it that maybe doesn't make an intermediate video that I have to chromakey ? I have access to the timestamps of the gestures as well as the duration these frames should stay on screen.

  


  my pipeline :

  


  Screen Frames w/ Timestamps+durations --> Concat-demux --> ---------------------------+
                                                                                      |
Gesture Logs --> Frames w/ timestamp+duration --> Concat-demux ---> chromakey --+     |
                    (has transparency)        (loses transparency)              |     |
                                                                                V     V
                                                                               Overlay
                                                                                  |
                                                                                  V
                                                                             Final Video


  


  Example frame from gestures which is the foreground
(The white is transparent)

  


  The background has no transparency as it is a computer background

  


  The command I used to combine the videos I generated is :
ffmpeg -i gestures.mp4 -i screen.mp4 -filter_complex '[0]chromakey=0x000000:.1[bk];[1][bk]overlay' output.mp4

  


• Convert wav to mp3 using Meteor FS Collections on Startup

  28 juillet 2015, par TheBetterJORT

  I’m trying to transcode all wav files into a mp3 using Meteor and Meteor FS Collections. My code works when I upload a wav file to the uploader — That is it will convert the wav to a mp3 and allow me to play the file. But, I’m looking for a Meteor Solution that will transcode and add the file to the DB if the file is a wav and exist in a certain directory. According to the Meteor FSCollection it should be possible if the files have already been stored. Here is their example code : *GM is for ImageMagik, I’ve replaced gm with ffmpeg and installed ffmpeg from atmosphereJS.

  Images.find().forEach(function (fileObj) {
  
    var readStream = fileObj.createReadStream('images');
  
    var writeStream = fileObj.createWriteStream('images');
  
    gm(readStream).swirl(180).stream().pipe(writeStream);
  
  });

  I’m using Meteor-CollectionFS [https://github.com/CollectionFS/Meteor-CollectionFS]-

  if (Meteor.isServer) {
  
    Meteor.startup(function () {
  
          Wavs.find().forEach(function (fileObj) {
  
        var readStream = fileObj.createReadStream('.wavs/mp3');
  
        var writeStream = fileObj.createWriteStream('.wavs/mp3');
  
        this.ffmpeg(readStream).audioCodec('libmp3lame').format('mp3').pipe(writeStream);
  
        Wavs.insert(fileObj, function(err) {
  
        console.log(err);
  
      });
  
        });
  
        });
  
  }

  And here is my FS.Collection and FS.Store information. Currently everything resides in one JS file.

  Wavs = new FS.Collection("wavs", {
  
    stores: [new FS.Store.FileSystem("wav"),
  
      new FS.Store.FileSystem("mp3",
  
  
  
      {
  
        path: '~/wavs/mp3',
  
        beforeWrite: function(fileObj) {
  
          return {
  
            extension: 'mp3',
  
            fileType: 'audio/mp3'
  
          };
  
        },
  
        transformWrite: function(fileObj, readStream, writeStream) {
  
          ffmpeg(readStream).audioCodec('libmp3lame').format('mp3').pipe(writeStream);
  
        }
  
      })]
  
  });

  When I try and insert the file into the db on the server side I get this error : MongoError : E11000 duplicate key error index :

  Otherwise, If I drop a wav file into the directory and restart the server, nothing happens. I’m new to meteor, please help. Thank you.