Converts FLAC/MP3 input, resamples down to ReplayGain levels, and converts to MP3. Requires on the path: flac, metaflac, ffmpeg, mogrify

ConvertTo-MP3.ps1

param(
    [string][Parameter(Mandatory=$true)]$InputFile,
    [string][Parameter(Mandatory=$true)]$OutputFile,
    [int]$SampleRate = 44100,
    [string]$BitRate = "160k"
)

$ErrorActionPreference = "Stop"

$InputFile = [System.IO.Path]::Combine((Get-Location), $InputFile)
$OutputFile = [System.IO.Path]::Combine((Get-Location), $OutputFile)
$OutputFilePath = [System.IO.Path]::GetDirectoryName($OutputFile)
if ((Test-Path -LiteralPath $OutputFilePath) -eq $false) {
    New-Item -type directory -path $OutputFilePath | out-null
}

$TempFile = [System.IO.Path]::GetTempFileName()

$ErrorActionPreference = "Continue"

try {
    ffmpeg -i "$InputFile" -y -ar $SampleRate -ac 2 -b:a $BitRate -map_metadata 0 -id3v2_version 3 "$OutputFile" 2>&1 >$TempFile
    if ($global:LASTEXITCODE -ne 0) {
        Get-Content $TempFile
        Write-Error "ffmpeg failure"
        exit -1
    }
}
finally {
    Remove-Item -LiteralPath $TempFile -ErrorAction Ignore
}

$Error.Clear()

update-mp3.ps1

param(
    [string]$srcFolder = "D:\Music\2.0",
    [string]$destFolder = "D:\Music\2.0_MP3"
)

$srcFolder = Resolve-Path $srcFolder.Trim("\")
$destFolder = Resolve-Path $destFolder.Trim("\")
$lastFolder = $null

$TempFile = [System.IO.Path]::GetTempFileName()

$ErrorActionPreference = "Continue"

try {
    Get-ChildItem -Recurse -Include @("*.mp3", "*.flac") $srcFolder | %{
        $src = $_.FullName
        $folder = Split-Path $src
        if ($folder -ne $lastFolder) {
            Write-Progress -Activity $folder
            $lastFolder = $folder
        }

        $dest = $_.FullName.Replace($srcFolder, $destFolder)
        $dest = ((Join-Path ([System.IO.Path]::GetDirectoryName($dest)) ([System.IO.Path]::GetFileNameWithoutExtension($dest))) + ".mp3")

        $srcWrite = ([System.IO.FileInfo]$src).LastWriteTime
        $destWrite = ([System.IO.FileInfo]$dest).LastWriteTime

        if ($destWrite -lt $srcWrite) {
            $destPath = [System.IO.Path]::GetDirectoryName($dest)
            if ((Test-Path -LiteralPath $destPath) -eq $false) {
                New-Item -type directory -path $destPath | out-null
            }

            Write-Host -ForegroundColor Blue -NoNewline "Converting: "
            Write-Host $src.Replace($srcFolder, "").Trim("\")

            if ($_.Name.EndsWith(".mp3")) {
                # Convert to FLAC
                & ffmpeg -y -i "$src" "$($dest).flac" 2>&1 >$TempFile
                if ($global:LASTEXITCODE -ne 0) {
                    Get-Content $TempFile
                    Write-Error "ffmpeg failure"
                    exit -1
                }
            } else {
                # Copy the FLAC file
                Copy-Item -LiteralPath $src -Destination "$($dest).flac"
            }

            # Remove unwanted tags
            & metaflac --remove-tag=unsyncedlyrics --remove-tag=lyrics --remove-tag=account_id --remove-tag=copyright "$($dest).flac" 2>&1 >$TempFile

            # Extract tags
            & metaflac --export-tags-to="$($dest).tags" "$($dest).flac" 2>&1 >$TempFile
            if ($global:LASTEXITCODE -ne 0) {
                Get-Content $TempFile
                Write-Error "metaflac failure"
                exit -1
            }

            # Extract cover art
            & ffmpeg -y -i "$src" "$($dest).jpg" 2>&1 >$TempFile

            # Resample to a stable volume level
            & flac -f -d "$($dest).flac" -o "$($dest).wav" --apply-replaygain-which-is-not-lossless=5a --delete-input-file 2>&1 >$TempFile
            if ($global:LASTEXITCODE -ne 0) {
                Get-Content $TempFile
                Write-Error "flac failure"
                exit -1
            }

            # Encode into FLAC so we can import the tags & image
            & flac -f "$($dest).wav" -o "$($dest).flac" --delete-input-file 2>&1 >$TempFile
            if ($global:LASTEXITCODE -ne 0) {
                Get-Content $TempFile
                Write-Error "flac failure"
                exit -1
            }

            # Import tags
            & metaflac --import-tags-from="$($dest).tags" --remove-replay-gain "$($dest).flac" 2>&1 >$TempFile
            if ($global:LASTEXITCODE -ne 0) {
                Get-Content $TempFile
                Write-Error "metaflac failure"
                exit -1
            }
            Remove-Item -LiteralPath "$($dest).tags" -ErrorAction Stop

            # Resize and import cover art
            if (Test-Path -LiteralPath "$($dest).jpg") {
                & mogrify -resize "800x800>" -quality 90 "$($dest).jpg"
                & metaflac --import-picture-from="$($dest).jpg" "$($dest).flac" 2>&1 >$TempFile
                Remove-Item -LiteralPath "$($dest).jpg" -ErrorAction Stop
            }

            # Final step, convert the resampled, properly tagged FLAC into MP3
            ConvertTo-MP3 "$($dest).flac" $dest -BitRate "320k"
            Remove-Item -LiteralPath "$($dest).flac" -ErrorAction Stop
        }
    }
}
finally {
    Remove-Item $TempFile -Force
}

$Error.Clear()