Capture ffmpeg's metadata output in powershell - powershell

Question

I'm trying to capture the output of ffmpeg in PowerShell(tm) to get some metadata on some ogg & mp3 files. But when I do:
ffmpeg -i file.ogg 2>&1 | sls GENRE
The output includes a bunch of lines without my matching string, "GENRE":
album_artist : Post Human Era
ARTIST : Post Human Era
COMMENT : Visit http://posthumanera.bandcamp.com
DATE : 2013
GENRE : Music
TITLE : Supplies
track : 1
At least one output file must be specified
I am guessing something is different in the encoding. ffmpeg's output is colored, so maybe there are color control characters in the output that are breaking things? Or, maybe ffmpeg's output isn't playing nicely with powershell's default UTF-16? I can't figure out if there is another way to redirect stderr and remove the color characters or change the encoding of stderr.
EDIT:
Strangely, I also get indeterminate output. Sometimes the output is as shown above. Sometimes with precisely the same command the output is:
GENRE :
Which makes slightly more sense, but is still missing the part of the line I care about ('Music').
Somewhere powershell is interpreting something as newlines that is not newlines.

Answer 1

I am still seeing this behavior when I use the old powershell, but I have since upgraded to PowerShell Core (7.0.2), and the problem seems to be solved. I read somewhere that with PowerShell Core they've changed the default encoding to UTF-8, so perhaps it is something related to that.
My theory is that in the old version, whatever code combines the outputstreams normally would make sure that individual lines were preserved and interleaved instead of of cut up. But I would guess that this code is looking for newlines in the default encoding, not UTF-8, so when it receives two UTF-8 streams it doesn't parse the line delimiters correctly and you get weird splits. It seems like there should be a way to change the encoding before it gets to mixing the output streams, but I'm not sure (and now it doesn't matter since it works). Why the output seems to change nondeterministically, I don't know, unless there is something nondeterministic about parsing UTF8 bytes as if they were UTF16 or whatever the default is.

Answer 2

I got something working for my script catching all the output with regex and pipe to a custom object
Function Rotate-Video {
param(
[STRING]$FFMPEGEXE = "P:\Video Editing\ffmpeg-4.3.1-2020-10-01-full_build\bin\ffmpeg.exe",
[parameter(ValueFromPipeline = $true)]
[STRING]$Source = "D:\Video\Source",
[STRING]$Destination = 'D:\Video\Destination',
[STRING]$DestinationExtention='mp4'
)
(Get-ChildItem $Source) | ForEach-Object {
$FileExist = $false
$Source = $_.fullname
$Name = $_.basename
$outputName = $name+'.'+$DestinationExtention
$Fullpath = Join-Path -Path $Destination -ChildPath $outputName
$Regex = "(\w+)=\s+(\d+)\s+(\w+)=(\d+.\d+)\s+(\w)=(\d+.\d+)\s+(\w+)=\s+(\d+)\w+\s+(\w+)=(\d+:\d+:\d+.\d+)\s+(\w+)=(\d+.\d+)\w+\/s\s+(\w+)=(\d+.\d+)"
&$FFMPEGEXE -i $Source -vf transpose=clock $Fullpath 2>&1 | Select-String -Pattern $Regex | ForEach-Object {
$output = ($_ | Select-String -Pattern $regex).Matches.Groups
[PSCUSTOMOBJECT]#{
Source = $source
Destination = $Fullpath
$output[1] = $output[2]
$output[3] = $output[4]
$output[5] = $output[6]
$output[7] = $output[8]
$output[9] = $output[10]
$output[11] = $output[12]
$output[13] = $output[14]
}
}
}
}