fluent-ffmpeg extract audio using streaming

Question

I'm trying to extract audio from video. This code works well:

ffmpeg('1.mp4').output('1.mp3')
.noVideo()
.format('mp3')
.outputOptions('-ab','192k')
.run();

But if I read the file with a stream like this:

var video = fs.createReadStream('1.mp4');
var audio = fs.createWriteStream('1.mp3');
ffmpeg(video).output(audio)
.noVideo()
.format('mp3')
.outputOptions('-ab','192k')
.run();

The output file weighs 1KB and does not have anything in it.

How can I extract audio using streams?

Answer 1

For further investigation, I added a callback for different sort of errors while transcoding, as well as other events. First hint was the following callback on progress event:

{ frames: NaN,
  currentFps: NaN,
  currentKbps: NaN,
  targetSize: 0,
  timemark: '00:00:00.00' }

As well, there was a stderr event:

ffmpeg version n4.1 Copyright (c) 2000-2018 the FFmpeg developers
  built with gcc 8.2.1 (GCC) 20180831
  configuration: --prefix=/usr --disable-debug --disable-static --disable-stripping --enable-fontconfig --enable-gmp --enable-gnutls --enable-gpl --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libdrm --enable-libfreetype --enable-libfribidi --enable-libgsm --enable-libiec61883 --enable-libjack --enable-libmodplug --enable-libmp3lame --enable-libopencore_amrnb --enable-libopencore_amrwb --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libv4l2 --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxcb --enable-libxml2 --enable-libxvid --enable-nvdec --enable-nvenc --enable-omx --enable-shared --enable-version3
  libavutil      56. 22.100 / 56. 22.100
  libavcodec     58. 35.100 / 58. 35.100
  libavformat    58. 20.100 / 58. 20.100
  libavdevice    58.  5.100 / 58.  5.100
  libavfilter     7. 40.101 /  7. 40.101
  libswscale      5.  3.100 /  5.  3.100
  libswresample   3.  3.100 /  3.  3.100
  libpostproc    55.  3.100 / 55.  3.100
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x562c9e18de80] stream 0, offset 0x30: partial file
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x562c9e18de80] Could not find codec parameters for stream 0 (Video: h264 (avc1 / 0x31637661), none, 240x180, 374 kb/s): unspecified pixel format
Consider increasing the value for the 'analyzeduration' and 'probesize' options
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'pipe:0':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf54.63.104
  Duration: 00:00:14.72, start: 0.000000, bitrate: N/A
    Stream #0:0(und): Video: h264 (avc1 / 0x31637661), none, 240x180, 374 kb/s, 25 fps, 25 tbr, 12800 tbn, 25600 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #0:1(und): Audio: aac (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 75 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
Stream mapping:
  Stream #0:1 -> #0:0 (aac (native) -> mp3 (libmp3lame))
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x562c9e18de80] stream 1, offset 0xa1e: partial file
pipe:0: Invalid data found when processing input
Output #0, mp3, to 'pipe:1':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    TSSE            : Lavf58.20.100
    Stream #0:0(und): Audio: mp3 (libmp3lame), 44100 Hz, stereo, fltp, 192 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
      encoder         : Lavc58.35.100 libmp3lame
size=       0kB time=00:00:00.00 bitrate=N/A speed=   0x    
{ frames: NaN,
  currentFps: NaN,
  currentKbps: NaN,
  targetSize: 0,
  timemark: '00:00:00.00' }
video:0kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
Output file is empty, nothing was encoded (check -ss / -t / -frames parameters if used)

The latter explains the empty file you're seeing in the output. As to why the error only happens while streaming the file, and not while opening it through another method, this answer explains the details: https://stackoverflow.com/a/40028894/1494833

Unfortunately the library doesn't yet support movflags input option as recommended above (https://github.com/fluent-ffmpeg/node-fluent-ffmpeg/issues/823).

Answer 2

ffmpeg doesn't like using using streams as inputs in my experience. the following code worked for me, first let ffmpeg do its thing, then create/play with streams for the input/output:

         let video = `${files[0].filename}`;
         readstream.pipe(fs.createWriteStream(`./${video}`))
           .on('error', () => {
             console.log("Some error occurred in download:" + error);
             res.send(error);
           })
           .on('finish', () => {
             let audio = `${video.split(".")[0]}.mp3`
             ffmpeg(`${video}`).output(audio)
               .noVideo()
               .format(`mp3`)
               .on(`end`, (stdout, stderr) => {
               let newReadstream = fs.createReadStream(`${audio}`);

               })
               .run()
}