private Task <Validation <BaseError, Unit> > FolderMustBeEmpty(StartFFmpegSession request)
    {
        string folder = Path.Combine(FileSystemLayout.TranscodeFolder, request.ChannelNumber);

        _logger.LogDebug("Preparing transcode folder {Folder}", folder);

        _localFileSystem.EnsureFolderExists(folder);
        _localFileSystem.EmptyFolder(folder);

        return(Task.FromResult <Validation <BaseError, Unit> >(Unit.Default));
    }