node.js : how to pipe - youtube to mp4 to mp3

Question

I want to convert a youtube url into an mp3 file. Currently, I download the mp4 using node's ytdl module, like so:

fs = require 'fs'
ytdl = require 'ytdl'

url = 'http://www.youtube.com/watch?v=v8bOTvg-iaU'
mp4 = './video.mp4'

ytdl(url).pipe(fs.createWriteStream(mp4))

Once the download is complete, I convert the mp4 into mp3 using the fluent-ffmpeg module, like so:

ffmpeg = require 'fluent-ffmpeg'

mp4 = './video.mp4'
mp3 = './audio.mp3'

proc = new ffmpeg({source:mp4})
proc.setFfmpegPath('/Applications/ffmpeg')
proc.saveToFile(mp3, (stdout, stderr)->
            return console.log stderr if err?
            return console.log 'done'
        )

I don't want to have to save the entire mp4 before starting the mp3 conversion. How do I pipe the mp4 into proc so it carries out the conversion as it receives the mp4 chunks?

Answer 1

Instead of passing the location of mp4 file, pass in the ytdl stream as the source, like so:

stream = ytdl(url)

proc = new ffmpeg({source:stream})
proc.setFfmpegPath('/Applications/ffmpeg')
proc.saveToFile(mp3, (stdout, stderr)->
            return console.log stderr if err?
            return console.log 'done'
        )