Xamarin Forms中LibVLC iOS端无法修改视频宽高比求助

我使用LibVLC播放视频，希望强制视频适配屏幕特定尺寸（允许轻微拉伸）。参考相关设置将MediaPlayer.Scale=0后，问题仍未解决。

在Grid首行添加VideoView后，Android端表现正常，但iOS端初始加载时视频周围会出现黑边，旋转设备横竖屏后黑边消失。看起来iOS是先渲染视频再应用宽高比，且仅在设备旋转时才会触发重绘。

我尝试过修改控件可见性、在UI线程（Device.BeginInvokeOnMainThread）中执行操作，均无效。该问题在普通Xamarin项目和Shell项目中均存在，测试设备为iPhone SE（iOS15.6）及iPhone13 Pro模拟器（iOS15.5）。

我基于libvlc-sharp-sample的MediaElement示例创建了简单测试项目。

XAML代码 #

<Grid BackgroundColor="LightGray" x:Name="MainGrid">
    <Grid.RowDefinitions>
        <RowDefinition Height="*"/>
        <RowDefinition Height="*"/>
          <shared:VideoView x:Name="VideoView"
                          Grid.Row="0" 
                          Grid.Column="0"
                          BackgroundColor="Black">

          </shared:VideoView>
    </Grid.RowDefinitions>
</Grid>

后台代码 #

protected async override void OnAppearing()
{
    base.OnAppearing();

    VideoView.MediaPlayerChanged += VideoView_MediaPlayerChanged;

    Core.Initialize();

    _libVLC = new LibVLC();

    CreateVideoPlayer();

}

async void CreateVideoPlayer()
{
 using (var media = new Media(_libVLC, new Uri(url)))
            {

                _mediaPlayer = new MediaPlayer(_libVLC)
                {
                    Media = media,
                    EnableHardwareDecoding = true,

                };
            }

            VideoView.MediaPlayer = _mediaPlayer;
            // 修正宽高比，让特殊分辨率的流填满Grid空间
            VideoView.MediaPlayer.AspectRatio = $"{Height}:{Width}";//"1920:1080";//Aspect.Fill.ToString();
            VideoView.MediaPlayer.Scale = 0;

            VideoView.MediaPlayer.EncounteredError += MediaPlayer_EncounteredError;
            VideoView.MediaPlayer.Stopped += MediaPlayer_Stopped;
            VideoView.MediaPlayer.Buffering += MediaPlayer_Buffering;
            VideoView.MediaPlayer.Opening += MediaPlayer_Opening;
            VideoView.MediaPlayer.PositionChanged += MediaPlayer_PositionChanged;
            VideoView.MediaPlayer.Playing += MediaPlayer_Playing;
}

• 延迟设置宽高比：在MediaPlayer.Playing事件触发后再设置适配规则，确保视频加载完成后再应用参数：

  private void MediaPlayer_Playing(object sender, EventArgs e)
  {
      Device.BeginInvokeOnMainThread(() =>
      {
          VideoView.MediaPlayer.AspectRatio = $"{VideoView.Width}:{VideoView.Height}";
          VideoView.MediaPlayer.Scale = 0;
      });
  }
  

• 强制触发iOS端重绘：通过自定义渲染器调用原生视图的SetNeedsDisplay()方法，确保参数生效后触发重绘：

  [assembly: ExportRenderer(typeof(VideoView), typeof(CustomVideoViewRenderer))]
  namespace YourProjectNamespace.iOS
  {
      public class CustomVideoViewRenderer : VideoViewRenderer
      {
          protected override void OnElementChanged(ElementChangedEventArgs<VideoView> e)
          {
              base.OnElementChanged(e);
              Control?.SetNeedsDisplay();
          }
  
          public override void LayoutSubviews()
          {
              base.LayoutSubviews();
              Control?.SetNeedsDisplay();
          }
      }
  }
  

• 调整LibVLC初始化参数：创建LibVLC实例时添加强制缩放的启动参数，提前指定缩放规则：

  _libVLC = new LibVLC(new string[] { "--no-video-autoscale", "--video-scale=0" });
  

内容的提问来源于stack exchange，提问作者dementedbroom