Make Video buffer more, download whole video in pause

I made Video streaming web with Blazor.

Razor page:

<BlazoredVideo EndedEvent="OnEnded" autoplay=true controls=true style="max-width:90%;">
  <source src=@streamingUrl />
</BlazoredVideo>

server side:

[HttpGet("{videoId}")]
public FileResult getFileByVideoId(string videoId = null)
{
  if (string.IsNullOrWhiteSpace(videoId))
  {
    return PhysicalFile($"{Config.PhysicalFilePath}/novideo.webm", "application/octet-stream", enableRangeProcessing: true);
  }
  var crawledVideo = dbContext.Crawled.FirstOrDefault(x => x.VideoId == videoId);
  return PhysicalFile($"{Config.PhysicalFilePath}/{crawledVideo.FullPath}", "application/octet-stream", enableRangeProcessing: true);
  //return PhysicalFile(path, MimeUtility.GetMimeMapping(fileName), fileName, true);
}

picture

as you can see on the picture, it buffers so little...

So when I go to slow internet area, Can't watch the video smoothly.

How can I make it buffers more and download whole video in pause?