# Copyright 2021 Microsoft

　　# This script will repair a FLAC file that has been corrupted by Media Foundation in reference to KB5003430 。

　　# Refer to KB5003430 for further information

　　param(

　　[parameter(Mandatory=$true，

　　HelpMessage=“The path to the FLAC file that has been corrupted by Media Foundation”，

　　ValueFromRemainingArguments=$true)]

　　[ValidateScript({ -not [String]：：IsNullOrEmpty($_) -and (Test-Path $_) })]

　　[String]$File

　　)

　　# We need to back up the current file incase we have any errors

　　$FileDirectory = Split-Path -Resolve $File

　　$Filename = Split-Path -Leaf -Resolve $File

　　$FullPath = Join-Path -Resolve $FileDirectory $Filename

　　$Filename = [String]：：Format(“Backup_{0：yyyyMMdd_hhmmss}_{1}”， [DateTime]：：Now， $Filename)

　　$BackupLocation = Join-Path $FileDirectory $Filename

　　Write-Output “Microsoft FLAC Repair Tool 。 This tool will repair a FLAC audio file that was corrupted when editing its details 。”

　　Write-Output “Affected File： $FullPath”

　　Write-Output “A backup of the file will be made： $BackupLocation”

　　Write-Output “Do you wish to continue？”

　　$choice=$host.ui.PromptForChoice(“Fixing FLAC Script”， “Do you wish to continue”， (‘&Yes’， ‘&No’)， 1)

　　function ParseStreamInfoMetadataBlock([System.IO.FileStream]$stream)

　　{

　　$blockType = $stream.ReadByte()

　　$lastBlock = ($blockType -shr 7) -ne 0

　　$blockType = $blockType -band 0x7F

　　if ($blockType -ne 0)

　　{

　　return $false

　　}

　　$blockSize = (($stream.ReadByte() -shl 16) -bor ($stream.ReadByte() -shl 8) -bor $stream.ReadByte())

　　if ($blockSize -lt 34)

　　{

　　return $false

　　}

　　$minAudioBlockSize = ($stream.ReadByte() -shl 8) -bor $stream.ReadByte()

　　$maxAudioBlockSize = ($stream.ReadByte() -shl 8) -bor $stream.ReadByte()

　　if ($minAudioBlockSize -lt 16 -or $maxAudioBlockSize -lt 16)

　　{

　　return $false

　　}

　　$minFrameSize = (($stream.ReadByte() -shl 16) -bor ($stream.ReadByte() -shl 8) -bor $stream.ReadByte())

　　$maxFrameSize = (($stream.ReadByte() -shl 16) -bor ($stream.ReadByte() -shl 8) -bor $stream.ReadByte())

　　$sampleInfo = (($stream.ReadByte() -shl 24) -bor ($stream.ReadByte() -shl 16) -bor ($stream.ReadByte() -shl 8) -bor $stream.ReadByte())

　　$sampleRate = $sampleInfo -shr 12

　　$channelCount = (($sampleInfo -shr 9) -band 0x7) + 1

　　$bitsPerSample = (($sampleInfo -shr 4) -band 0x1F) + 1

　　[UInt6?4]$sampleCount = (($stream.ReadByte() -shl 24) -bor ($stream.ReadByte() -shl 16) -bor ($stream.ReadByte() -shl 8) -bor $stream.ReadByte())

　　$sampleCount = (([UInt6?4]$sampleInfo -band 0xF) -shl 32) -bor $sampleCount

　　$MD5HashBytes = New-Object byte[] 16

　　$stream.Read($MD5HashBytes， 0， $MD5HashBytes.Length)

　　$MD5Hash = [Guid]($MD5HashBytes)

　　if ($sampleRate -eq 0)

　　{

　　return $false

　　}

　　# Passing these checks means that we likely have a stream info header and can rebuild the file

　　Write-Output “File Stream Information”

　　Write-Output “Sample Rate： $sampleRate”

　　Write-Output “Audio Channels： $channelCount”

　　Write-Output “Sample Depth： $bitsPerSample”

　　Write-Output “MD5 Audio Sample Hash： $MD5Hash”

　　return $true

　　}

　　if ($choice -eq 0)

　　{

　　Copy-Item $FullPath -Destination $BackupLocation -Force

　　$stream = [System.IO.File]：：Open($FullPath， [System.IO.FileMode]：：Open)

　　$stream.Seek(4， [System.IO.SeekOrigin]：：Begin)

　　while ($stream.ReadByte() -eq 0) {}

　　# We now need to figure out where a valid FLAC metadata frame begins

　　# We are likely pointing to the last byte of the size member so we‘ll seek back 4 bytes and retry

　　$flacDataStartPosition = $stream.Position - 4

　　$stream.Seek($flacDataStartPosition， [System.IO.SeekOrigin]：：Begin)

　　while (-not(ParseStreamInfoMetadataBlock($stream)))

　　{

　　$flacDataStartPosition = $flacDataStartPosition + 1

　　$stream.Seek($flacDataStartPosition， [System.IO.SeekOrigin]：：Begin)

　　}

　　# Insert the start code

　　$stream.Seek($flacDataStartPosition， [System.IO.SeekOrigin]：：Begin)

　　if (Test-Path “$FullPath.tmp”)

　　{

　　Remove-Item “$FullPath.tmp”

　　}

　　$fixedStream = [System.IO.File]：：Open(“$FullPath.tmp”， [System.IO.FileMode]：：CreateNew)

　　[byte[]]$startCode = [char[]](‘f’， ‘L’， ‘a’， ‘C’)；

　　$fixedStream.Write($startCode， 0， $startCode.Length)

　　$stream.CopyTo($fixedStream)

　　$stream.Close()

　　$fixedStream.Close()

　　Move-Item -Force “$FullPath.tmp” $FullPath

　　}