stream stdout causes RAM usage to increase dramatically

I use spawn to run a command that runs constantly (Not supposed to stop) and it transmits data to its output. The problem is that RAM usage of the node app increases constantly. After multiple tests, I could reach to following part of code that reproduces the problem, even though the functions are almost empty:

const runCommand = () => {

    const command = 'FFMPEG COMMAND HERE';
    let ffmpeg = spawn(command, [], { shell: true });

    ffmpeg.on('exit', function(code) { code = null; });

    ffmpeg.stderr.on('data', function (data) { data = null; });

    ffmpeg.stdout.on('data', function (data) { data = null; });

};

The important part is, when I delete function (data) {} from ffmpeg.stdout.on('data', function (data) {}); the problem goes away. Type of received data is buffer object. I think the problem is with that part.

UPDATE: After hours of research, I found out that it's something related to spawn output and stream backpressure. I configured FFMPEG command to send chunks less frequently. That mitigated the problem (Increasing less than before). But memory usage still increasing.

from stream stdout causes RAM usage to increase dramatically