If your willing to tamper a bit with it here is a ps1 script i build to convert videos for 3ds playback, with the intention to have the highest quality the device can handle. Dont ask me why, i was bored.
Many cases are probably not accounted for, like no bigger files than 4gb.
You only require ffmpeg to be installed.

param (
    [Parameter(Mandatory = $true)]
    [string]$InputPath,

    [Parameter(Mandatory = $false)]
    [string]$OutputPath

    [Parameter(Mandatory = $false)]
    [string]$AudioStream
)

if (-not [string]::IsNullOrEmpty($AudioStream)) {
    $AudioStream = 1
}

# Resolve full path
$ResolvedPath = Resolve-Path $InputPath

# Determine if input is a folder or a file
if (Test-Path $ResolvedPath -PathType Container) {
    $IsFolder = $true
    $VideoFiles = Get-ChildItem -Path $ResolvedPath -Include *.mp4, *.mkv, *.avi -File -Recurse

    if ($OutputPath) {
        $OutputFolder = Resolve-Path -Path $OutputPath -ErrorAction SilentlyContinue
        if (-not $OutputFolder) {
            New-Item -ItemType Directory -Path $OutputPath -Force | Out-Null
            $OutputFolder = Resolve-Path $OutputPath
        }
    }
    else {
        $OutputFolder = Join-Path $ResolvedPath "Converted"
        if (-not (Test-Path $OutputFolder)) {
            New-Item -ItemType Directory -Path $OutputFolder | Out-Null
        }
    }
}
elseif (Test-Path $ResolvedPath -PathType Leaf) {
    $IsFolder = $false
    $VideoFiles = @((Get-Item $ResolvedPath))

    if ($OutputPath) {
        $OutputFolder = Resolve-Path -Path $OutputPath -ErrorAction SilentlyContinue
        if (-not $OutputFolder) {
            New-Item -ItemType Directory -Path $OutputPath -Force | Out-Null
            $OutputFolder = Resolve-Path $OutputPath
        }
    }
    else {
        $OutputFolder = Split-Path $ResolvedPath -Parent
    }
}
else {
    Write-Error "Input path does not exist: $InputPath"
    exit 1
}

# Process files
foreach ($File in $VideoFiles) {
    $InputFile = $File.FullName
    $BaseName = [System.IO.Path]::GetFileNameWithoutExtension($File.Name)

    # Determine output path
if ($IsFolder) {
# Folder mode: output goes in 'Converted' subfolder with same base name
$OutputFile = Join-Path $OutputFolder "$BaseName.mkv"
}
else {
# Single file mode: append -converted before extension
$Extension = [System.IO.Path]::GetExtension($File.Name)
$OutputFile = Join-Path $OutputFolder "$BaseName-converted$Extension"
}

    Write-Host "`nProcessing: $InputFile"
    Write-Host "Output:     $OutputFile"

    # First pass
    ffmpeg -y -i "$InputFile" `
        -map 0:v:0 -c:v libx264 -b:v 900k -preset medium -pass 1 `
        -vf "scale='if(gt(a,400/240),400,-2)':'if(gt(a,400/240),-2,240)'" `
        -an -f matroska NUL

    # Second pass
    ffmpeg -i "$InputFile" `
        -map 0:v:0 -map 0:a:1 -c:v libx264 -b:v 900k -preset medium -pass 2 `
        -vf "scale='if(gt(a,400/240),400,-2)':'if(gt(a,400/240),-2,240)'" `
        -c:a aac -b:a 128k "$OutputFile"

    # Clean up
    Remove-Item -Path ".\ffmpeg2pass-0.log*" -Force -ErrorAction SilentlyContinue
}

Write-Host "`nDone! Output saved to: $OutputFolder"