问题描述
我解码使用内置摄像头的条形码，我这样做的 capElement.Source.CapturePhotoToStreamAsync 来捕获预览照片。它的工作原理，但冻结的应用程序的一瞬间，感觉很笨拙和马车。
I'm decoding barcodes using the built in camera, I do this with the capElement.Source.CapturePhotoToStreamAsync to capture photos from the preview. it works, but freezes the app for a brief moment, which feels very clumsy and buggy.
所以我想这个在后台同时至少留下一个响应UI在处理照片。
So I'd like to this in background while at least leaving a responsive UI while processing the photos.
到目前为止，我想出了这个以捕获视频流：
So far I came up with this to capture the video stream:
private async void ScanInBackground()
{
bool failedScan = true;
var stream = new InMemoryRandomAccessStream();
await capElement.Source.StartRecordToStreamAsync(MediaEncodingProfile.CreateWmv(VideoEncodingQuality.HD1080p), stream);
while(failedScan)
{
Byte[] bytes = await GetBytesFromStream(stream);
//How to split the bytes into frames?
Task.Delay(50);
}
Dispatcher.RunAsync(CoreDispatcherPriority.Low,() => StopCap());
}
和此方法来获取从流的字节数：
and this method to get the bytes from the stream:
public static async Task<byte[]> GetBytesFromStream(IRandomAccessStream randomStream)
{
var reader = new DataReader(randomStream.GetInputStreamAt(0));
var bytes = new byte[randomStream.Size];
try
{
await reader.LoadAsync((uint)randomStream.Size); reader.ReadBytes(bytes);
}
catch(Exception ex)
{
Logger.LogExceptionAsync(ex, "GetBytesFromStream");
}
return bytes;
}
从注释的 ScanInBackground ，你可以看到，我不知道如何分割流成照片/帧。
From the comment at the ScanInBackground, you can see that I have no clue how to split the stream into photos/frames.
推荐答案
有一个微软GitHub的页面上的样品是相关的，虽然他们面向Windows 10.您可能感兴趣的迁移项目中得到这个功能。
There is a sample on the Microsoft github page that is relevant, although they target Windows 10. You may be interested in migrating your project to get this functionality.
的：此示例将捕获预览画面，而不是全面的照片。一旦它有一个预览框，它能够读取和编辑它的像素
GetPreviewFrame: This sample will capture preview frames as opposed to full-blown photos. Once it has a preview frame, it can read and edit the pixels on it.
下面是相关的部分：
private async Task GetPreviewFrameAsSoftwareBitmapAsync()
{
// Get information about the preview
var previewProperties = _mediaCapture.VideoDeviceController.GetMediaStreamProperties(MediaStreamType.VideoPreview) as VideoEncodingProperties;
// Create the video frame to request a SoftwareBitmap preview frame
var videoFrame = new VideoFrame(BitmapPixelFormat.Bgra8, (int)previewProperties.Width, (int)previewProperties.Height);
// Capture the preview frame
using (var currentFrame = await _mediaCapture.GetPreviewFrameAsync(videoFrame))
{
// Collect the resulting frame
SoftwareBitmap previewFrame = currentFrame.SoftwareBitmap;
// Add a simple green filter effect to the SoftwareBitmap
EditPixels(previewFrame);
}
}
private unsafe void EditPixels(SoftwareBitmap bitmap)
{
// Effect is hard-coded to operate on BGRA8 format only
if (bitmap.BitmapPixelFormat == BitmapPixelFormat.Bgra8)
{
// In BGRA8 format, each pixel is defined by 4 bytes
const int BYTES_PER_PIXEL = 4;
using (var buffer = bitmap.LockBuffer(BitmapBufferAccessMode.ReadWrite))
using (var reference = buffer.CreateReference())
{
// Get a pointer to the pixel buffer
byte* data;
uint capacity;
((IMemoryBufferByteAccess)reference).GetBuffer(out data, out capacity);
// Get information about the BitmapBuffer
var desc = buffer.GetPlaneDescription(0);
// Iterate over all pixels
for (uint row = 0; row < desc.Height; row++)
{
for (uint col = 0; col < desc.Width; col++)
{
// Index of the current pixel in the buffer (defined by the next 4 bytes, BGRA8)
var currPixel = desc.StartIndex + desc.Stride * row + BYTES_PER_PIXEL * col;
// Read the current pixel information into b,g,r channels (leave out alpha channel)
var b = data[currPixel + 0]; // Blue
var g = data[currPixel + 1]; // Green
var r = data[currPixel + 2]; // Red
// Boost the green channel, leave the other two untouched
data[currPixel + 0] = b;
data[currPixel + 1] = (byte)Math.Min(g + 80, 255);
data[currPixel + 2] = r;
}
}
}
}
}
和声明这个类以外的：
[ComImport]
[Guid("5b0d3235-4dba-4d44-865e-8f1d0e4fd04d")]
[InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
unsafe interface IMemoryBufferByteAccess
{
void GetBuffer(out byte* buffer, out uint capacity);
}
当然，你的项目将允许不安全的代码，这一切工作。
And of course, your project will have to allow unsafe code for all of this to work.
有在样品仔细看看，看看如何让所有的细节。或者说，有一个演练中，您可以观看从相机会近期//构建/会议，其中包括通过一些相机样本演练一点点。
Have a closer look at the sample to see how to get all the details. Or, to have a walkthrough, you can watch the camera session from the recent //build/ conference, which includes a little bit of a walkthrough through some camera samples.
这篇关于WinRT的从视频中提取流帧的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！