如果你是一名音乐发烧友，那么应该知道Flac这种常见的无损音乐格式。Flac音乐文件支持metadata，用户可以编辑metadata，让音乐文件带有艺术家、所属专辑、音轨等等信息。
通常来说，metadata和音频数据并不相关，修改metadata并不会影响音频本身。
但是，近日微软官方公布了Win10中存在一个Bug，在Win10中用资源管理器修改Flac文件的metadata，竟会导致音频的损坏！
根据Windows Latest的报道，微软最新发布的一份支持文件披露，如果在Win10的2004或者更高版本中，使用文件资源管理器修改Flac音乐文件的metadata，就会损耗Flac音频文件。
这个Bug在Win10专业版、家庭版、企业版、工作站版乃至其他版本的Win10中均有出现。
根据微软本月早些时候发布的支持文件，Win10的文件资源管理器导致了这个错误，它破坏了Flac文件头包含的ID3框架也就是metadata，而这个ID3框架负责存储音频的注释，例如音乐标题、艺术家、专辑、曲目编号等。
在Win10上，Flac的处理程序忽视了ID3框架，该程序认为Flac文件在使用4字节的文件头，当Flac文件被Win10编辑的时候，ID3框架被覆盖了，导致没有了开始代码，导致了音乐播放器无法识别被修改后的文件。
因此，在Win10中，如果你直接用文件资源管理器修改Flac音乐文件的标题、艺术家等metadata，会导致该文件无法播放。
幸运的是，微软已经确定了Bug的根本原因，用户可以通过Windows Update升级KB5003214补丁进行修复。
在KB5003214补丁中，微软确认了上文提到的错误已经被修复，修改了Flac的标题、艺术家等metadata后，Flac不会再变得无法播放。
而对于已经损坏了的Flac文件，微软则发布了一个PowerShell脚本来进行修复，运行该脚本后Flac文件即可重新播放，不过已经从ID3框架中丢失了的metadata信息并不能恢复。
下面是利用PowerShell脚本修复Flac文件的具体方法。
1、开启记事本；
2、复制以下字符，粘贴到记事本中：
# 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“另存为”对话框中，将目录定位到你想要保存PowerShell脚本的位置；
4、在文件名输入框中，输入“FixFlacFiles.ps1”，将另存为文件的类型更改为Text Documents (*.txt)；
5、进入到你保存该PowerShell脚本的目录；
6、右键点击刚刚保存的脚本，然后选择“使用PowerShell运行”；
7、出现提示时，输入无法播放的Flac文件的文件名，然后按下回车键。
微软建议大家安装本月推送的可选累积更新，以避免修改Flac文件metadata出现的问题。
