Ffmpeg send duration of video to client (using node-fluent-ffmpeg)

I'm really new to the world of ffmpeg so please excuses me if this is a stupid queston.

I'm using the module Node-fluent-ffmpeg to stream a movie and convert it from avi to webm with FFMPEG.

So far so good (it plays the video), but I'm having trouble parsing the duration to the player. It also gives me an error even though I plays the video.

my code is as followed:

var stat = fs.statSync(movie);

var start = 0;
var end = 0;
var range = req.header('Range');
if (range != null) {
start = parseInt(range.slice(range.indexOf('bytes=')+6,
  range.indexOf('-')));
end = parseInt(range.slice(range.indexOf('-')+1,
  range.length));
}
if (isNaN(end) || end == 0) end = stat.size-1;
if (start > end) return;

var duration = (end / 1024) * 8 / 1024;

res.writeHead(206, { // NOTE: a partial http response
    'Connection':'close',
    'Content-Type':'video/webm',
    'Content-Length':end - start,
    'Content-Range':'bytes '+start+'-'+end+'/'+stat.size,
    'Transfer-Encoding':'chunked'
});

var proc = new ffmpeg({ source: movie, nolog: true, priority: 1, timeout:15000})
    .toFormat('webm')
    .addOptions(['-probesize 900000', '-analyzeduration 0', '-minrate 1024k', '-maxrate 1024k', '-bufsize 1835k', '-t '+duration+' -ss'])
    .writeToStream(res, function(retcode, error){
    if (!error){
        console.log('file has been converted succesfully',retcode);
    }else{
        console.log('file conversion error',error);
    }
});

I set the header with a start and a end based on this article: http://delog.wordpress.com/2011/04/25/stream-webm-file-to-chrome-using-node-js/

I calculate the length in seconds in the variable duration.

The error FFmpeg is giving me is:

    file conversion error ffmpeg version N-52458-gaa96439 Copyright (c) 2000-2013 the FFmpeg developers
      built on Apr 24 2013 22:19:32 with gcc 4.8.0 (GCC)
      configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-avisynth --enable-bzlib --enable-fontconfig --e
    nable-frei0r --enable-gnutls --enable-iconv --enable-libass --enable-libbluray --enable-libcaca --enable-libfreetype --enable
    -libgsm --enable-libilbc --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --ena
    ble-libopus --enable-librtmp --enable-libschroedinger --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libtwola
    me --enable-libvo-aacenc --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libxavs --enabl
    e-libxvid --enable-zlib
      libavutil      52. 27.101 / 52. 27.101
      libavcodec     55.  6.100 / 55.  6.100
      libavformat    55.  3.100 / 55.  3.100
      libavdevice    55.  0.100 / 55.  0.100
      libavfilter     3. 60.101 /  3. 60.101
      libswscale      2.  2.100 /  2.  2.100
      libswresample   0. 17.102 /  0. 17.102
      libpostproc    52.  3.100 / 52.  3.100
    Input #0, avi, from 'C:/temp/test.avi':
      Metadata:
        encoder         : Nandub v1.0rc2
      Duration: 00:01:09.78, start: 0.000000, bitrate: 1517 kb/s
        Stream #0:0: Video: msmpeg4v3 (DIV3 / 0x33564944), yuv420p, 640x352, 23.98 tbr, 23.98 tbn, 23.98 tbc
        Stream #0:1: Audio: mp3 (U[0][0][0] / 0x0055), 48000 Hz, stereo, s16p, 222 kb/s
    [libvpx @ 0036db20] v1.2.0
    Output #0, webm, to 'pipe:1':
      Metadata:
        encoder         : Lavf55.3.100
        Stream #0:0: Video: vp8, yuv420p, 640x352, q=-1--1, 200 kb/s, 1k tbn, 23.98 tbc
        Stream #0:1: Audio: vorbis, 48000 Hz, stereo, fltp
    Stream mapping:
      Stream #0:0 -> #0:0 (msmpeg4 -> libvpx)
      Stream #0:1 -> #0:1 (mp3 -> libvorbis)

The client side player (which is VideoJs) says the file is infinite/NaN in length.

I feel like I'm pretty close to a solution but my inexperience with the subject matter prohibits me from getting it to work. If I'm unclear in any way please let me know. (I have a tendency of explaining things fuzzy.)

Thanks in advance!

[EDIT]

I removed the duration bit because it has nothing to do with the issue. I checked the response header of the client and saw:

 Accept-Ranges:bytes
 Connection:keep-alive
 Content-Length:13232127
 Content-Range:bytes 0-13232127/13232128
 Content-Type:video/webm

Why can't the client figure out the duration even though it receives it in the header?