使用smil网址更改视频分辨率

Question

我正在使用以下代码通过url下载视频，以默认分辨率下载视频很酷。在这里，我想在下载开始时更改视频分辨率。我有要使用的Smill文件网址。但是我坚持在哪里提供输入来更改视频轨道。

    NSURLSessionConfiguration *urlSessionConfiguration = [NSURLSessionConfiguration backgroundSessionConfigurationWithIdentifier:@"assetDowloadConfigIdentifier"];
    AVAssetDownloadURLSession *avAssetDownloadSession = [AVAssetDownloadURLSession sessionWithConfiguration:urlSessionConfiguration assetDownloadDelegate:self delegateQueue:[NSOperationQueue mainQueue]];
    NSURL *assetURL = [NSURL URLWithString:@"https://a4i6tw1.xyzcdn.com/vistvorigin/smil:e30d690b7b3bc8ac5da2049f50c80794c762423e.smil/playlist.m3u8"];

   if (@available(iOS 10.0, *)) {

        AVAssetDownloadTask *avAssetDownloadTask = [avAssetDownloadSession assetDownloadTaskWithURLAsset:hlsAsset assetTitle:@"downloadedMedia" assetArtworkData:nil options:nil];

        // Start task and begin download
        [avAssetDownloadTask resume];

    } else {
        // Fallback on earlier versions
    }