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• Workflow and data format for sending MediaRecorder output to express server

  30 avril 2021, par Max

  I've been trying to figure this out for a while but got lost between different ways of sending files and different data formats.

  


  I am recording the stream of a canvas animation with MediaRecorder. As far as I understand this returns a blob with the video in binary format. Now I want to send this data to my express server and convert it to an h264 encoded mp4 file. My first impulse was to use ffmpeg on the server. Unfortunately I'm struggling with the details of the implementation. I am unsure on how to best transmit the data and in what format and how to feed it to ffmpeg.

  


  This is what I have on the client side :

  


  // Get stream from element
stream = element.captureStream(30)

// Create media recorder with stream
const recorder = new MediaRecorder(stream)

// Save to file
recorder.ondataavailable = ({ data }) => {
                
    const formData = new FormData()
    formData.append("file", data)

    const options = {
        method: "POST",
        body: formData,
    }

    fetch("http://localhost:3001/api/blob_to_mp4", options).then(
        (res) => {
            console.log(res)
        }
    )
}


  


  And this is what I have on the server side :

  


  "use strict";

const express = require("express");
const cors = require("cors");
const ffmpeg = require("fluent-ffmpeg");
const fs = require("fs");

const port = process.env.PORT || 3001;
const app = express();
var command = ffmpeg();

app.use(cors());
app.use(express.urlencoded({ extended: true }));
app.use(express.json());

app.post("/api/blob_to_mp4", function (req, res) {
  var data = Buffer.from("");

  // Add data
  req.on("data", function (chunk) {
    data = Buffer.concat([data, chunk]);
  });

  // Full data available
  req.on("end", () => {
    req.rawBody = data;
  });

  res.send("hello world");
});

app.listen(port);
console.log(`Server running on port ${port}`);


  


• ffmpeg run from c# Process not closing when using '-i anullsrc'

  1er octobre 2022, par Brown Bear

  I am generating a large collection MP4 videos from an OpenGL source. This has worked perfectly so far but I recently noticed that some TV media player don't like video without audio, see here for more info.

  


  So far i hve been using the following code :

  


      private bool StartRecording()
    {
        _ffmpeg = new Process();
        _ffmpeg.StartInfo.FileName = "ffmpeg.exe";
        _ffmpeg.StartInfo.Arguments = $"-f rawvideo -pix_fmt rgba -s {RecordSize.Width}x{RecordSize.Height} -r 30 -i - -c libx264 -crf 17 -pix_fmt yuv420p -b:v 1024k -bufsize:v 1835008 {RecordFile} -tune animation";
        _ffmpeg.StartInfo.RedirectStandardInput = true;
        _ffmpeg.Start();

        if(_ffmpeg.HasExited)
        {
            IsRecording = false;
            return false;
        }
        return true;
    }

    private void RecordFrame(RenderUpdate update)
    {
        if (_ffmpeg == null)
            return;

        var frame = Project.RecordFrame(update);
        var data = new byte[frame.Length];
        var height = RecordSize.Height;
        var width = RecordSize.Width;

        for (var k = 0; k < height; k++)
        {
            var j = height - k - 1;
            Buffer.BlockCopy(
                frame, k * width * 4,
                data, j * width * 4,
                width * 4);
        }

        _ffmpeg.StandardInput.BaseStream.Write(data, 0, data.Length);
    }

    private void StopRecording()
    {
        Project.StopRecording();
        if (_ffmpeg == null)
            return;

        _ffmpeg.StandardInput.Flush();
        _ffmpeg.StandardInput.Close();
        _ffmpeg.Close();
        _ffmpeg.Dispose();
    }


  


  And it has worked perfectly until I modified the 'ffmpeg' cmd line arguments to include '-i anullsrc' for the audio.

  


    _ffmpeg.StartInfo.Arguments = $"-f rawvideo -pix_fmt rgba -s {RecordSize.Width}x{RecordSize.Height} -r 30 -i - -f lavfi -i anullsrc=channel_layout=mono:sample_rate=8k -c:v libx264 -crf 17 -pix_fmt yuv420p -b:v 1024k -bufsize:v 1835008 {RecordFile} -tune animation";


  


  The moment I add '-f lavfi -i anullsrc' to the cmd line the call to 'StopRecording()' has no effect and ffmpeg continues to run.

  


  I can manually stop it by closing the console window or even using ctrl-c, but the job needs to be automated so this is just not an option.

  


  Ultimately my question is Why is ffmpeg behaving this way ?

  


  I've come up with a couple of work arounds, but I don't like either :

  


  

  1. Post process the videos as per the link I mentioned earlier. Not practical. I need to generate 1000s of videos and a single batch of 350 takes around 6 hours. 50% of that time is consumed by ffmpeg encoding, so to re-encode them all just to add a null audio track would nearly double the time.

  


  2. Try to push a 'ctrl-c' through to the ffmpeg process as per this post. I did some quick tests with 'GenerateConsoleCtrlEvent' without sucess, and the idea of having to manually start and stop the Process via 'kernel32.dll' seems excessive not to mention old school.

  


  


  Any insight would be greatly appreciated.

  


• Revision 3202 : Et on update la conf d’emballe_medias tant qu’à faire

  6 avril 2010, par kent1 — Log

  Et on update la conf d’emballe_medias tant qu’à faire