How can you combine audio and video streams in Node.js and send them to the client through piping?

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To combine audio and video streams in Node.js and send them to the client through piping, you can use the FFmpeg library. FFmpeg has a node module called fluent-ffmpeg that allows you to manipulate audio and video streams programmatically. Here's how to do it:

1. Install FFmpeg and the fluent-ffmpeg module:

npm install ffmpeg fluent-ffmpeg

1. Create a new ffmpeg instance and input the audio and video streams:

const ffmpeg = require('fluent-ffmpeg');

// Create an ffmpeg instance with the audio and video streams
const command = ffmpeg()
  .input(audioStream)
  .input(videoStream)

1. Add any additional processing to the streams, such as resizing or adding filters:

// Resize the video to a specific size
command.videoSize('640x480')

// Add a video filter to adjust brightness and contrast
command.videoFilter([
    `eq=brightness=${brightness}:contrast=${contrast}`
])

1. Add an output format and pipe the output to the response:

// Set the output format to mp4
command.format('mp4')

// Pipe the output to the response
const headers = {
  'Content-Type': 'video/mp4',
  'Content-Disposition': 'attachment; filename=video.mp4',
}
response.writeHead(200, headers)
command.pipe(response)

1. Start the ffmpeg process:

// Start the ffmpeg process
command.run()

This will create a combined audio and video stream and send it to the client through piping. You can customize this process to suit your needs, including adding more inputs or building more complex processing chains.