Program.cs

using AssetsTools.NET;
using AssetsTools.NET.Extra;

if (args.Length is < 1 or > 2) {
	Console.WriteLine("Usage: Rebundle_LZMA <input_bundle> [output_bundle]");
	Console.WriteLine("Compresses an asset bundle using LZMA compression");
	Console.WriteLine("If no [output_bundle] is specified, the compressed file will be saved with '_LZMA' added to the input filename");
	return 1;
}

string inputPath = args[0];
string outputPath;

if (!File.Exists(inputPath)) {
	Console.WriteLine($"Error: Input file '{inputPath}' not found.");
	return 1;
}

if (args.Length == 1) { //input only
	outputPath = Path.Combine(
		Path.GetDirectoryName(inputPath)!,
		$"{Path.GetFileNameWithoutExtension(inputPath)}_LZMA{Path.GetExtension(inputPath)}"
	);
} else { //output folder or file specified
	string outputPart = args[1];
	if (Path.HasExtension(outputPart)) {
		outputPath = outputPart;
	} else {
		outputPath = Path.Combine(outputPart, $"{Path.GetFileName(inputPath)}");
	}
}

if (string.IsNullOrEmpty(outputPath)) {
	Console.WriteLine("Error: Output path is invalid.");
	return 1;
}

string? output = Path.GetDirectoryName(outputPath);
//not empty, create output directory if needed
if (!string.IsNullOrWhiteSpace(output)) {
	Console.WriteLine($"Creating output directory: {output}");
	Directory.CreateDirectory(output);
}

try {
	Console.WriteLine($"Loading bundle from: {inputPath}");

	var assetsManager = new AssetsManager();
	var bundle = assetsManager.LoadBundleFile(inputPath);

	try {
		Console.WriteLine("Compressing bundle with LZMA...");
		using var outputStream = File.Create(outputPath);
		using var outputWriter = new AssetsFileWriter(outputStream);
		bundle.file.Pack(outputWriter, AssetBundleCompressionType.LZMA);

		Console.WriteLine($"Successfully compressed bundle to: {outputPath}");
		return 0;
	} finally {
		assetsManager.UnloadBundleFile(bundle);
	}
} catch (Exception ex) {
	Console.WriteLine($"Error: {ex.Message}");
	return 1;
}