Converts audio FLAC to ac3 via Powershell and FFMPEG

audio_to_ac3.ps1

Get-ChildItem -Filter *.mkv | ForEach-Object {
    $outputFile = $_.BaseName + "_ac3.mkv"
    
    # Get information about audio streams
    $audioStreams = ffprobe -v error -select_streams a -show_entries stream=index,codec_name -of csv=p=0 $_.FullName | ForEach-Object {
        $stream = $_ -split ','
        [PSCustomObject]@{
            Index = [int]$stream[0]
            Codec = $stream[1]
        }
    }
    
    $ffmpegCommand = "ffmpeg -i `"$($_.FullName)`" -map 0 -c copy"
    
    foreach ($stream in $audioStreams) {
        if ($stream.Codec -eq 'flac') {
            $ffmpegCommand += " -c:a:$($stream.Index) ac3"
        }
    }
    
    $ffmpegCommand += " `"$outputFile`""
    
    Write-Host "Processing file: $($_.Name)"
    Write-Host "Command: $ffmpegCommand"
    
    Invoke-Expression $ffmpegCommand
}