InvalidCastException inside MonoTouch's AVFoundation.AVA
本文关键字:AVFoundation AVA inside MonoTouch InvalidCastException | 更新日期: 2023-09-27 18:28:40
我正在尝试一个非常简单的程序:使用AVFoundation加载资源视频,并将视频帧字节作为OpenGL纹理获取。
一般流程非常简单:
- 我将视频加载到
AVAsset
- 然后我将视频音轨放入
AVAssetReaderTrackOutput
- 我把它插入
AVAssetReader
- 我开始阅读
- 对于每一个视频帧,我得到一个
CMSampleBuffer
,从中得到CVPixelBuffer
- 然后我锁定
CVPixelBuffer
,并用GL.TexImage2D
将其上传到OpenGL中
它在模拟器中运行得很好,但当我在实际设备中尝试时,第一步就会出现以下错误:
System.InvalidCastException: Cannot cast from source type to destination type.
at MonoTouch.AVFoundation.AVAsset.FromUrl (MonoTouch.Foundation.NSUrl url) [0x00011] in /Developer/MonoTouch/Source/monotouch/src/AVFoundation/AVAsset.g.cs:231
at MyTestApp.EAGLView.LoadVideo () [0x00033] in /Volumes/Shared/MyTestApp/MyTestApp/EAGLView.cs:191
引发异常的代码如下所示:
private AVAsset videoAsset;
private AVAssetReaderTrackOutput videoReaderOutput;
private AVAssetReader videoReader;
private void LoadVideo()
{
var videoPath = NSBundle.MainBundle.PathForResource("video", "mp4");
var videoURL = NSUrl.FromFilename(videoPath);
Console.WriteLine ("Loading from " + videoURL.ToString ());
object videoAssetRaw = AVAsset.FromUrl(videoURL); // Exception thrown here
videoAsset = videoAssetRaw as AVAsset;
var tracks = videoAsset.Tracks;
NSError error;
AVAssetTrack videoTrack = tracks[0];
AVVideoSettings settings = new AVVideoSettings ();
settings.PixelFormat = CVPixelFormatType.CV32BGRA;
videoReaderOutput = AVAssetReaderTrackOutput.FromTrack(videoTrack, settings.ToDictionary());
videoReader = new AVAssetReader (videoAsset, out error);
videoReader.AddOutput (videoReaderOutput);
videoReader.StartReading ();
}
我直接将其放入object
而不是AVAsset
,只是为了确保InvalidCastException
不会被抛出到我这边,但当异常读取时,它被抛出到AVAsset.g.cs
的第231行,而我没有。
视频文件是作为"BundleResource"构建的,我使用的是最新版本的xamarin(今天早些时候下载)。
有什么想法可能导致这种情况吗?
不如。。。
object videoAssetRaw = AVAsset.FromUrl(videoURL);
尝试。。。
AVUrlAssetOptions options = null;
var asset = new AVUrlAsset (url, options);