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• ffmpeg not reading stdin fast enough

  5 mars 2019, par Joshua Walsh

  I have a NodeJS program which launches ffmpeg (with child_process) and then provides realtime video data via stdin, using the pipe protocol.

  ffmpeg -nostdin -i pipe:0 -codec libx264 -preset veryfast -tune zerolatency -acodec aac -b:a 128k output/index.m3u8

  ffmpeg transcodes the video into h264 and muxes it into an HLS live stream.

  The issue that I have is that sometimes ffmpeg refuses to accept more input. The default behaviour of NodeJS is to buffer input until the child process can accept it, but after a while this causes my application to run out of memory.

  I tried a naive solution where if ffmpeg wasn’t able to read the input (if proc.stdin.write returns false) I would start discarding data until the drain event was raised on the stream, but this unsurprisingly led to badly degraded video output, with terrible artifacting.

  The nature of the source of the data makes it impossible for me to block, my application has to deal with it in realtime.

  ffmpeg is using only a fraction of the available resources on the system (35% CPU, 1% disk), so I’m not sure why it’s blocking stdin. If I specify a more demanding preset then it happily uses more CPU, so CPU speed shouldn’t be a limiting factor.

  Does anyone know why ffmpeg would be blocking stdin ? Is there a way I can tell ffmpeg to drop frames if it starts falling behind ?

• Node.js Live Streaming : Avoid buffering

  27 octobre 2012, par Shirish Kamath

  I've written a small nodeJS server that outputs system audio captured by ffmpeg on Windows (using DirectShow) to the browser as a streaming MP3 file. The audio needs to be as live as possible, with minimum/no buffering, and a "skipping" effect in the audio is perfectly acceptable.

  When I play the audio in Chrome using the HTML5 audio tag, there's a delay of about 8-10 secs over a low-latency LAN connection. I suspected this to be a client-side buffer, and used a Flash MP3 player on the client-side, which brought down the delay to 2-3 secs.

  Now, the buffering seems to taking place on the server-side. The documentation for NodeJS's response.write mentions that the data is written kernel buffers. How do I go about avoiding any buffering altogether or at least getting around it, so that the client always gets the latest audio data ? Strategies for handling 'drain' events to always push live data ?

  On the request object, I've used setNoDelay(true) to avoid the use of Nagle's algorithm. Following is a snippet of how data is written when the spawned ffmpeg process emits data.

  var clients = []; //List of client connections currently being served
  
  ffmpeg.stdout.on('data', function(data) {
  
      for(var i = 0; i < clients.length; i++){
  
          clients[i].res.write(data);
  
      }
  
  });

• DirectShow IVideoWindow can't be wider than 4096px

  25 mars 2019, par ulvesked

  I have a C# application which uses DirectShow to show play video clips. We recently tried to play a video that is 9600x1080 px and it would not show. DirectShow emits events that everything.

  We use K-Lite codec pack (1295) and utilise ffdshow libx264 as codec and video renderer. Media Player Classic using the same renderer can play the clip just fine. The latest version of our application use DirectShow.NET while the older versions call DirectShow interfaces directly. Both old and new versions of our application have the same issues.

  After some experimentation we have found out the following :

  • If the video window width is 4096px or narrower it will render video. If it is 4097 or wider it will not render any video. We tried playing a HD-clip and a 720-clip with the same results. They will play when the video window is 4096x1080 but not when the window is 4097x1080 or wider.

  • When changing resolution or graphic settings there are some flashes (a few frames) of the video when the settings is applied, so that would suggest that it is in fact playing the video but it displays only black.

  Tested on Windows 10, 64 bit.

  Any ideas of what the we can do to fix this ?