Question

Im trying to automate video conversion with powershell and ffmpeg tool.
Ffmpeg have detailed output about video if called without all nessesary parameters. Usually it reports about error and display input file info if one specified.
Ex I interactively executed such command:

d:\video.Enc\ffmpeg.exe -i d:\video.Enc\1.wmv

this is powershell console output

ffmpeg.exe : FFmpeg version SVN-r20428, Copyright (c) 2000-2009 Fabrice Bellard, et al.
row:1 char:24
+ d:\video.Enc\ffmpeg.exe <<<<  -i d:\video.Enc\1.wmv
    + CategoryInfo          : NotSpecified: (FFmpeg version ...Bel 
   lard, et al.:String) [], RemoteException
    + FullyQualifiedErrorId : NativeCommandError

  built on Nov  1 2009 04:03:50 with gcc 4.2.4
  configuration: --enable-memalign-hack --prefix=/mingw --cross-pre
fix=i686-mingw32- --cc=ccache-i686-mingw32-gcc --target-os=mingw32 
--arch=i686 --cpu=i686 --enable-avisynth --enable-gpl --enable-vers
ion3 --enable-zlib --enable-bzlib --enable-libgsm --enable-libfaad 
--enable-pthreads --enable-libvorbis --enable-libtheora --enable-li
bspeex --enable-libmp3lame --enable-libopenjpeg --enable-libxvid --
enable-libschroedinger --enable-libx264 --enable-libopencore_amrwb 
--enable-libopencore_amrnb
  libavutil     50. 3. 0 / 50. 3. 0
  libavcodec    52.37. 1 / 52.37. 1
  libavformat   52.39. 2 / 52.39. 2
  libavdevice   52. 2. 0 / 52. 2. 0
  libswscale     0. 7. 1 /  0. 7. 1
[wmv3 @ 0x144dc00]Extra data: 8 bits left, value: 0

Seems stream 1 codec frame rate differs from container frame rate: 
1000.00 (1000/1) -> 15.00 (15/1)
Input #0, asf, from 'd:\video.Enc\1.wmv':
  Duration: 00:12:0
2.00, start: 5.000000, bitrate: 197 kb/s
    Stream #0.0(eng): Audio: wmav2, 44100 Hz, 1 channels, s16, 48 k
b/s
    Stream #0.1(eng): Video: wmv3, yuv420p, 1024x768, 137 kb/s, 15 tbr, 1k tbn, 1k tbc Metadata
    title           : Silverlight 2.0 Hello World Application
    author          : Sergey Pugachev
    copyright       : 
    comment         : 
    WMFSDKVersion   : 11.0.6001.7000
    WMFSDKNeeded    : 0.0.0.0000
    IsVBR           : 1
    ASFLeakyBucketPairs: 
    VBR Peak        : 715351
    Buffer Average  : 127036
At least one output file must be specified

But I cant figure how to script this and capture output to any kind of posh objects.
I tried direct script, wher ps1 file contained exact expression “d:\video.Enc\ffmpeg.exe -i d:\video.Enc\1.wmv” – it didnt work. Also i tried to do that with invoke-command and invoke expression. First one returns an exact string with command, second one – dump error to output console but not to -ErrorVariable i specified ( I did set all out variables, not only error one – all of them were empty).

Can anyone point to correct syntax for invoking console applications in posh and capturing output ?

Second one question will be about parsing that output – I’ll need video resolution data to calculate correct aspect ratio for conversion. So it will be cool if anyone point how to work with captured error output and parse string like

Stream #0.1(eng): Video: wmv3, yuv420p, 1024×768,

Answer 1

Try redirecting the error stream to stdout like so and then you should be able to capture both stdout and stderr in a single variable e.g.:

$res = d:\video.Enc\ffmpeg.exe -i d:\video.Enc\1.wmv 2>&1

To capture the data try this:

$res | Select-String '(?ims)^Stream.*?(\d{3,4}x\d{3,4})' -all | 
    %{$_.matches} | %{$_.Groups[1].Value}

I’m not sure if $res will be one string or multiple but the above should work for both cases.