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• Check an address to see if there is any video stream on it or not

  12 janvier 2014, par Blue Sky

  I want to read a video stream from a UDP address using libavcodec functions. To do so, I use the following code :

   char *url = "udp://127.0.0.1:1000";
  
   AVFormatContext *oc = NULL;
  
   avformat_open_input(&oc, url, NULL , NULL);

  If we run this code, then function "avformat_open_input" starts listening on the given UDP address, and it looks like the program is halted if there is no video stream at the given UDP address.

  Now, I want to write a code to first check the given UDP address quickly to see whether there is any data on it or not, if there is no data then the program should neglect running "avformat_open_input", otherwise it should run this function so that I can avoid the halting situation.

  Any idea how I can do this ? Thanks !

• Streaming converted movie with mp4 container in NodeJS, movie playing very fast

  20 septembre 2016, par Mustafa

  I have used stream-transcoder module to convert a file make it a stream. So the file is not stored, it is on the fly.

  app.get("/video", function(req,res){
  
      res.writeHead(200, {'Content-Type': 'video/mp4'});
  
      var src = "movie.avi";
  
  
  
      var Transcoder = require('stream-transcoder');
  
      var stream = fs.createReadStream(src);
  
      new Transcoder(stream)
  
          .maxSize(1280, 720)
  
          .videoCodec('h264')
  
          .videoBitrate(800 * 1000)
  
          .fps(25)
  
          .sampleRate(44100)
  
          .channels(2)
  
          .audioBitrate(128 * 1000)
  
          .format('mp4')
  
          .on('finish', function() {
  
              console.log("finished");
  
          })
  
          .stream().pipe(res);
  
  });

  It works nicely, it is fast, but too fast, the audio is played at the same speed, however the video does not respect the frame rate, whatever is recieved from ffmpeg is immeidately shown, fastly. Additionally, it does not show the total time, I believe it is the problem. I need to somehow specify the length, framerate, but I could not find enough information on that. I thought the stream recieved from ffmpeg should contain that. And I could not find respective headers for that in HTTP.

  Here are the flags that this stream-transcoder module uses for MP4 :

  [ '-i',
  
    '-',
  
    '-vf',
  
    'scale=min(trunc(1280/hsub)*hsub\\,trunc(a*720/hsub)*hsub):min(trunc(720/vsub)*vsub\\,trunc(1280/a/vsub)*vsub)',
  
    '-vcodec',
  
    'h264',
  
    '-b:v',
  
    800000,
  
    '-r',
  
    25,
  
    '-ar',
  
    44100,
  
    '-ac',
  
    2,
  
    '-ab',
  
    128000,
  
    '-f',
  
    'mp4',
  
    '-movflags',
  
    'frag_keyframe+faststart',
  
    'pipe:1' ]

  When I use VP8 encoder and WebM, it works nicely, the time is displayed, video plays normal speed.

• Delay in displaying a video stream after streaming by libavformat

  15 janvier 2014, par Blue Sky

  I am using libavformat library to stream a video at a network address like udp ://127.0.0.1:1000. I use ffplay to display the received video stream at the network address. However, the video appears few second later (e.g. 5 6 seconds) at ffplay on the same machine. Do you know what is the reason ?

  More info :

  I have written my own streaming application using libavformat. When I stream a 3sec 1080p video at 25fps, ffplay does not show anything. If I repeat streaming the same video once again, this time, ffplay starts displaying the previous streamed video as well as the current video. So, it looks like ffplay waits for a buffer to be filled up by some amount, and then displays the stream. But am I correct ?