WIN10 - How to modify STDERR before writing to an outfile

Question

In windows, How does one change STDERR before writing it to an out file?

The goal is to create one log file containing all the ffmpeg integrity errors.

ffmpeg-recursive-error.bat

@echo off
set "_var1_DoHeading=ZZZ"
FOR /R "S:#MiscDownloads\test&quot; %%G IN (*.mp4) DO (
  echo Processing... %%G
  set "_var1_DoHeading=YES"
  echo [a - The value of _var1_DoHeading is %_var1_DoHeading% ]
  for /f "usebackq delims==" %%H in (ffmpeg.exe -xerror -v error -i &quot;%%G&quot; -f null - 2^&gt;^&amp;1) do (
    if %_var1_DoHeading%==YES (
      echo ====================
      echo %%G
    )
    set "_var1_DoHeading=NO"
    echo [b - The value of _var1_DoHeading is %_var1_DoHeading% ]
    echo %%H
  )

)
echo Done

Error

PS C:\duplicate-file-finder> .\ffmpeg-check-for-errors.bat

Processing... S:#MiscDownloads\test\test_video.mp4

[a - The value of _var1_DoHeading is ZZZ ]

[b - The value of _var1_DoHeading is ZZZ ]

[aac @ 000001b1848bed40] channel element 0.0 is not allocated

[b - The value of _var1_DoHeading is ZZZ ]

[h264 @ 000001b184936b80] error while decoding MB 60 21, bytestream -7

Done

References:

score 0 · Answer 1 · answered Jan 11 '20 at 17:30

There are no environment variables for STDIN and STDERR. You need to explicitly pipe them into some other command.

I would suggest this syntax:

for /f "delims=" %%a in ('ffmpeg ... 2^>^&1') do set "myvar=%%a"

The output of ffmpeg will become the value of myvar and can be used by %myvar%.

The ^ is the batch escape character. If you will need quotes for parameters in the ffmpeg command, use the usebackq option for replacing them with back-quotes.

For more information see the FOR /F command.

WIN10 - How to modify STDERR before writing to an outfile

1 Answers1