如果你是一名音樂發燒友，那么應該知道Flac這種常見的無損音樂格式。Flac音樂文件支持metadata，用戶可以編輯metadata，讓音樂文件帶有藝術家、所屬專輯、音軌等等信息。
通常來說，metadata和音頻數據并不相關，修改metadata并不會影響音頻本身。
但是，近日微軟官方公布了Win10中存在一個Bug，在Win10中用資源管理器修改Flac文件的metadata，竟會導致音頻的損壞!
根據Windows Latest的報道，微軟最新發布的一份支持文件披露，如果在Win10的2004或者更高版本中，使用文件資源管理器修改Flac音樂文件的metadata，就會損耗Flac音頻文件。
這個Bug在Win10專業版、家庭版、企業版、工作站版乃至其他版本的Win10中均有出現。
根據微軟本月早些時候發布的支持文件，Win10的文件資源管理器導致了這個錯誤，它破壞了Flac文件頭包含的ID3框架也就是metadata，而這個ID3框架負責存儲音頻的注釋，例如音樂標題、藝術家、專輯、曲目編號等。
在Win10上，Flac的處理程序忽視了ID3框架，該程序認為Flac文件在使用4字節的文件頭，當Flac文件被Win10編輯的時候，ID3框架被覆蓋了，導致沒有了開始代碼，導致了音樂播放器無法識別被修改后的文件。
因此，在Win10中，如果你直接用文件資源管理器修改Flac音樂文件的標題、藝術家等metadata，會導致該文件無法播放。
幸運的是，微軟已經確定了Bug的根本原因，用戶可以通過Windows Update升級KB5003214補丁進行修復。
在KB5003214補丁中，微軟確認了上文提到的錯誤已經被修復，修改了Flac的標題、藝術家等metadata后，Flac不會再變得無法播放。
而對于已經損壞了的Flac文件，微軟則發布了一個PowerShell腳本來進行修復，運行該腳本后Flac文件即可重新播放，不過已經從ID3框架中丟失了的metadata信息并不能恢復。
下面是利用PowerShell腳本修復Flac文件的具體方法。
1、開啟記事本;
2、復制以下字符，粘貼到記事本中：
# 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
[UInt64]$sampleCount = (($stream.ReadByte() -shl 24) -bor ($stream.ReadByte() -shl 16) -bor ($stream.ReadByte() -shl 8) -bor $stream.ReadByte())
$sampleCount = (([UInt64]$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
}
3、保存文件，在“另存為”對話框中，將目錄定位到你想要保存PowerShell腳本的位置;
4、在文件名輸入框中，輸入“FixFlacFiles.ps1”，將另存為文件的類型更改為Text Documents (*.txt);
5、進入到你保存該PowerShell腳本的目錄;
6、右鍵點擊剛剛保存的腳本，然后選擇“使用PowerShell運行”;
7、出現提示時，輸入無法播放的Flac文件的文件名，然后按下回車鍵。
微軟建議大家安裝本月推送的可選累積更新，以避免修改Flac文件metadata出現的問題。
