我正在尝试从网络摄像头获取每一帧的位图。
我按照这个 Microsoft 教程使用 MediaFrameReader 处理媒体帧。其他一些视频格式(YUY2、NV12...)工作正常,但选择和设置 MJPG 格式会导致ArgumentException: 'Value does not fall within the expected range.'
.MediaFrameReader.TryAcquireLatestFrame()
这是我设置网络摄像头媒体源和处理 FrameArrived 事件的工作代码:
private async Task StartReadFrameAsync()
{
MediaFrameSourceInfo colorSourceInfo = null;
MediaFrameSourceGroup selectedGroup = null;
var frameSourceGroups = await MediaFrameSourceGroup.FindAllAsync();
foreach (var sourceGroup in frameSourceGroups)
{
foreach (var sourceInfo in sourceGroup.SourceInfos)
{
if (sourceInfo.MediaStreamType == MediaStreamType.VideoRecord && sourceInfo.SourceKind == MediaFrameSourceKind.Color)
{
colorSourceInfo = sourceInfo;
break;
}
}
if (colorSourceInfo != null)
{
selectedGroup = sourceGroup;
break;
}
}
var settings = new MediaCaptureInitializationSettings
{
VideoDeviceId = deviceId,
SourceGroup = selectedGroup,
MemoryPreference = MediaCaptureMemoryPreference.Cpu
};
var mediaCapture = new MediaCapture();
await mediaCapture.InitializeAsync(settings);
var colorFrameSource = mediaCapture.FrameSources[colorSourceInfo.Id];
var preferredFormat = colorFrameSource.SupportedFormats.FirstOrDefault(format =>
{
return format.Subtype == MediaEncodingSubtypes.Mjpg && format.VideoFormat.Width >= 720;
});
if (preferredFormat == null)
return;
await colorFrameSource.SetFormatAsync(preferredFormat);
mediaFrameReader = await mediaCapture.CreateFrameReaderAsync(colorFrameSource, MediaEncodingSubtypes.Mjpg);
mediaFrameReader.FrameArrived += MediaFrameReader_FrameArrived;
await mediaFrameReader.StartAsync();
}
private async void MediaFrameReader_FrameArrived(MediaFrameReader sender, MediaFrameArrivedEventArgs args)
{
var mediaFrameReference = sender.TryAcquireLatestFrame(); // <- throws ArgementException
var videoMediaFrame = mediaFrameReference?.VideoMediaFrame;
var softwareBitmap = videoMediaFrame?.SoftwareBitmap;
//...
}
我测试了两个网络摄像头,它们支持 MJPG 格式,并且我还检查了在CaptureElement
控件中预览 MJPG 格式是否有效。只有TryAcquireLatestFrame()
在事件中MediaFrameReader_FrameArrived
才会抛出。
问题:
我做错了什么,MediaFrameReader
无法获取 MJPG 帧?