spawn in Bun Fails to Properly Handle FFmpeg Custom Pipes (e.g., pipe:3)

[pxgo]

What version of Bun is running?

1.2.4

What platform is your computer?

Microsoft Windows NT 10.0.26100.0 x64

What steps can reproduce the bug?

const { spawn } = require('child_process');

class ExecModule {
  run(app, args, callback) {
    return new Promise((resolve, reject) => {
      const child = spawn(
        app,
        args.map((i) => i.toString())
      );
      const stdoutChunks = [];
      const stderrChunks = [];

      child.stdout?.on('data', (chunk) => {
        stdoutChunks.push(chunk);
        if (callback) callback(chunk);
      });

      child.stderr?.on('data', (chunk) => {
        stderrChunks.push(chunk);
      });

      child.on('close', (code) => {
        const stdout = Buffer.concat(stdoutChunks);
        const stderr = Buffer.concat(stderrChunks).toString('utf8');

        if (code === 0) {
          resolve(stdout);
        } else {
          reject(
            new Error(
              `Process exited with code ${code}\n` + `[STDERR] ${stderr.trim()}`
            )
          );
        }
      });

      child.on('error', (err) => {
        reject(
          new Error(
            `Process failed to start: ${err.message}\n` +
            `[STDERR] ${Buffer.concat(stderrChunks).toString('utf8').trim()}`
          )
        );
      });
    });
  }
}

class AudioModule {
  sampleRate = 44100;
  format = 'mp3';
  bitrate = '128k';
  async getMuteBufferForever(callback) {
    return await execModule.run(
      'ffmpeg',
      [
        '-re',
        '-f',
        'lavfi',
        '-i',
        'anullsrc=cl=stereo:r=44100',
        '-ac',
        '2',
        '-ar',
        this.sampleRate,
        '-b:a',
        this.bitrate,
        '-f',
        this.format,
        'pipe:1',
      ],
      callback
    );
  }
}

const audioModule = new AudioModule();
const execModule = new ExecModule();

async function main() {

  const ffmpeg = spawn(
    'ffmpeg',
    ['-re', '-i', 'pipe:3', '-f', 'mp3', 'pipe:1'],
    {
      stdio: ['pipe', 'pipe', 'pipe', 'pipe'],
    }
  );

  ffmpeg.stdout.on('data', (data) => {
    console.log('stdout', data);
  });
  ffmpeg.stderr.on('data', (data) => {
    console.error(`FFmpeg Error:`);
    console.log(data.toString());
  });
  ffmpeg.on('close', (code) => {
    console.log('close', code);
  });
  ffmpeg.on('error', (err) => {
    console.log('error', err);
  });

  audioModule.getMuteBufferForever((buffer) => {
    ffmpeg.stdio[3].write(buffer);
  });
}
main().catch(console.error);

What is the expected behavior?

The following code will be triggered repeatedly:

ffmpeg.stdout.on('data', (data) => {
  console.log('stdout', data);
});

Console output:

What do you see instead?

The following code is not triggered:

ffmpeg.stdout.on('data', (data) => {
  console.log('stdout', data);
});

Additional information

Problem Description

When using Bun's child_process.spawn to invoke FFmpeg, I observed that when FFmpeg parameters specify a custom input pipe (e.g., -i pipe:3) and data is written to the corresponding stdio[3], FFmpeg does not receive the data, resulting in no output and potential process blocking. However, the same code works as expected in the Node.js environment. This suggests that Bun's spawn implementation may have an issue handling additional pipes beyond the standard stdin, stdout, and stderr.

Bun vs NodeJS(v20.14.0)

Bun:

NodeJS: