M4A 파일이 뭔가요 — 여는 법과 MP3 로 바꾸는 법 (설치 없이)

Add-Type -AssemblyName System.Runtime.WindowsRuntime
$ms = [System.WindowsRuntimeSystemExtensions].GetMethods()
$op = ($ms | Where-Object { $_.Name -eq 'AsTask' -and $_.GetParameters().Count -eq 1 -and $_.GetParameters()[0].ParameterType.Name -like 'IAsyncOperation*' })[0]
$ap = ($ms | Where-Object { $_.Name -eq 'AsTask' -and $_.GetParameters().Count -eq 1 -and $_.GetParameters()[0].ParameterType.Name -like 'IAsyncActionWithProgress*' })[0]
function Wait-Op($o, $t) { $x = $op.MakeGenericMethod($t).Invoke($null, @($o)); $x.Wait(-1) | Out-Null; $x.Result }
function Wait-Act($a) { $x = $ap.MakeGenericMethod([double]).Invoke($null, @($a)); $x.Wait(-1) | Out-Null }

[Windows.Storage.StorageFile,   Windows.Storage, ContentType=WindowsRuntime] | Out-Null
[Windows.Storage.StorageFolder, Windows.Storage, ContentType=WindowsRuntime] | Out-Null
[Windows.Media.MediaProperties.MediaEncodingProfile, Windows.Media, ContentType=WindowsRuntime] | Out-Null
[Windows.Media.Transcoding.MediaTranscoder, Windows.Media, ContentType=WindowsRuntime] | Out-Null

$folderPath = "C:\Users\you\Music"          # .m4a 파일이 있는 폴더
$folder  = Wait-Op ([Windows.Storage.StorageFolder]::GetFolderFromPathAsync($folderPath)) ([Windows.Storage.StorageFolder])
$profile = [Windows.Media.MediaProperties.MediaEncodingProfile]::CreateMp3("High")

Get-ChildItem "$folderPath\*.m4a" | ForEach-Object {
    $src  = Wait-Op ([Windows.Storage.StorageFile]::GetFileFromPathAsync($_.FullName)) ([Windows.Storage.StorageFile])
    $dst  = Wait-Op ($folder.CreateFileAsync([IO.Path]::ChangeExtension($_.Name, ".mp3"), 1)) ([Windows.Storage.StorageFile])
    $t    = New-Object Windows.Media.Transcoding.MediaTranscoder
    $prep = Wait-Op ($t.PrepareFileTranscodeAsync($src, $dst, $profile)) ([Windows.Media.Transcoding.PrepareTranscodeResult])
    if ($prep.CanTranscode) { Wait-Act ($prep.TranscodeAsync()); "$($_.Name) -> $($dst.Name)" }
    else { "$($_.Name): $($prep.FailureReason)" }
}