Develop Reference

Best way to stream low latency video from a Raspberry Pi to an UWP-APP

For a project, I have to communicate with a Raspberry Pi Zero from a UWP-APP via TCP. Because both, the Raspberry and the computer with the interface, have got a private IP, I have to use a server to forward messages from one client to the other one. This part already works but now my problem is that I have to implement video streaming from the Raspberry to the UWP-APP.
Because my partner is in charge of creating and designing the UWP-APP, I have made myself a little Test-Interface with WindowsForms. I have tried several techniques like Netcat the video output over the server to the client or direct TCP-streaming with raspivid, but the best solution so far is the one I found in this project here. But instead of using the Eneter.Messaging-library I use my own class for communication with TcpClients.
I use mono to run my C# script on the Raspberry and the code to stream the Video looks like this:
while (true)
{
//Wait with streaming until the Interface is connected
while (!RemoteDeviceConnected || VideoStreamPaused)
{
Thread.Sleep(500);
}
//Check if Raspivid-Process is already running
if(!Array.Exists(Process.GetProcesses(), p => p.ProcessName.Contains("raspivid")))
raspivid.Start();
Thread.Sleep(2000);
VideoData = new byte[VideoDataLength];
try
{
while (await raspivid.StandardOutput.BaseStream.ReadAsync(VideoData, 0, VideoDataLength) != -1 && !VideoChannelToken.IsCancellationRequested && RemoteDeviceConnected && !VideoStreamPaused)
{
// Send captured data to connected clients.
VideoConnection.SendByteArray(VideoData, VideoDataLength);
}
raspivid.Kill();
Console.WriteLine("Raspivid killed");
}
catch(ObjectDisposedException)
{
}
}
Basically, this method just reads the h264 data from the Standard-Output-Stream of the raspivid process in chunks and sends it to the server.
The next method runs on the server and just forwards the byte array to the connected interface-client.
while (RCVVideo[id].Connected)
{
await RCVVideo[id].stream.ReadAsync(VideoData, 0, VideoDataLength);
if (IFVideo[id] != null && IFVideo[id].Connected == true)
{
IFVideo[id].SendByteArray(VideoData, VideoDataLength);
}
}
SendByteArray() uses the NetworkStream.Write() Method.
On the interface, I write the received byte[] to a named pipe, to which the VLC-Control connects to:
while (VideoConnection.Connected)
{
await VideoConnection.stream.ReadAsync(VideoData, 0, VideoDataLength);
if(VideoPipe.IsConnected)
{
VideoPipe.Write(VideoData, 0, VideoDataLength);
}
}
Following code initializes the pipe-server:
// Open pipe that will be read by VLC.
VideoPipe = new NamedPipeServerStream(#"\raspipipe",
PipeDirection.Out, 1,
PipeTransmissionMode.Byte,
PipeOptions.WriteThrough, 0, 10000);
And for VLC:
LibVLC libVLC = new LibVLC();
videoView1.MediaPlayer = new MediaPlayer(libVLC);
videoView1.MediaPlayer.Play(new Media(libVLC, #"stream/h264://\\\.\pipe\raspipipe", FromType.FromLocation));
videoView1.MediaPlayer.EnableHardwareDecoding = true;
videoView1.MediaPlayer.FileCaching = 0;
videoView1.MediaPlayer.NetworkCaching = 300;
This works fine on the Windowsforms-App and I can get the delay down to 2 or 3 seconds (It should be better in the end but it is acceptable). But on the UWP-App I can't get it to work even after adding /LOCAL/ to the pipe name. It shows that the VLC-Control connects to the pipe, and I can see that data is written to the pipe but it doesn't display video.
So my question is:
How can I get this to work with the VLC-Control (LibVLCSharp) in UWP? Am I missing something fundamental?
Or is there even a better way to stream the video in this case?
I have researched a bit on the UWP-MediaPlayerElement to but I can't find a way to get my byte[] into it.

First of all, thank you for your quick responses and interesting ideas!
I took a look into Desktop Bridge but it is not really what I wanted, because my colleague has already put in a lot of effort to design the UWP-APP and my Windows-Form is just a botch to try things out.
But the thing that really worked for me was StreamMediaInput . I have no idea how I missed this before. This way I just passed my NetworkStream directly to the MediaPlayer without using a Named-Pipe.
LibVLC libVLC = new LibVLC();
videoView1.MediaPlayer = new MediaPlayer(libVLC);
Media streamMedia = new Media(libVLC, new StreamMediaInput(Client.Channels.VideoConnection.stream), ":demux=h264");
videoView1.MediaPlayer.EnableHardwareDecoding = true;
videoView1.MediaPlayer.FileCaching = 0;
videoView1.MediaPlayer.NetworkCaching = 500;
videoView1.MediaPlayer.Play(streamMedia);
This solution is now working for me both, in UWP and in Windows-Forms.

Get current state of webcam in C#

I am trying to figure out how to check if a webcam/video capture device is already being used by another application without actually activating it.
My current approach is to use the AForge.NET library and using the .IsRunning property of the VideoCaptureDevice object like this:
var videoDevices = new FilterInfoCollection(FilterCategory.VideoInputDevice);
foreach (FilterInfo videoDevice in videoDevices)
{
VideoCaptureDevice camera new AForge.Video.DirectShow.VideoCaptureDevice(videoDevice.MonikerString);
Debug.Print(camera.IsRunning)
}
I guess the IsRunning property only works on VideoCaptureDevices that have been started using the library and I need lower-level DirectShow access to the device.
While there are many ways to use DirectShow in C#, I have been unable to find a way to check the state even using DirectShow in C++. Is there some magic I need to perform here?
Thanks
Tobias Timpe

I'm not entirely sure if this will be helpful to you, but I found your question because I wanted to write a custom app to control my busylight. This is very much 'Works On My Machine' certified - it's not an attempt to give a general answer. However, I figure it may help you, and possibly the next person who comes across this page while googling...
private static bool IsWebCamInUse()
{
using (var key = Registry.CurrentUser.OpenSubKey(#"SOFTWARE\Microsoft\Windows\CurrentVersion\CapabilityAccessManager\ConsentStore\webcam\NonPackaged"))
{
foreach (var subKeyName in key.GetSubKeyNames())
{
using (var subKey = key.OpenSubKey(subKeyName))
{
if (subKey.GetValueNames().Contains("LastUsedTimeStop"))
{
var endTime = subKey.GetValue("LastUsedTimeStop") is long ? (long) subKey.GetValue("LastUsedTimeStop") : -1;
if (endTime <= 0)
{
return true;
}
}
}
}
}
return false;
}

Bluetooth BLE Battery Level - C#

I have an specific issue about the Bluetooth BLE API on Windows 10.
At the moment I'm programming a tool on C# (Visual Studio) which connects itself to a given BLE - Device. Currently the connection works perfect and I can read out the ServiceUUIDs and the CharacterUUIDs.
The main Problem is after I try to read the value of the Character its always returns me 00. I heard that implementing a notification will change that and I followed these instructions but they didn't help me.
(Here are the Specifications from bluetooth.com:)
My Code:
//connect to BluetoothDevice
var device = await BluetoothLEDevice.FromIdAsync(address);
//get UUID of Services
var services = await device.GetGattServicesAsync();
if (services != null)
{
foreach (var servicesID in services.Services)
{
//if there is a service thats same like the Battery Service
if (servicesID.Uuid.ToString() == BluetoothBLE.Constants.BATTERY_SERVICE)
{
//updateServiceList is like a console logging in my tool
updateServiceList($"Service: {servicesID.Uuid}");
var characteristics = await servicesID.GetCharacteristicsAsync();
foreach (var character in characteristics.Characteristics)
{
if (Constants.BATTERY_LEVEL == character.Uuid.ToString())
{
updateServiceList("C - UUID: "+ character.Uuid.ToString());
GattReadResult result = await character.ReadValueAsync();
if (result.Status == GattCommunicationStatus.Success)
{
var reader = DataReader.FromBuffer(result.Value);
byte[] input = new byte[reader.UnconsumedBufferLength];
reader.ReadBytes(input);
System.Diagnostics.Debug.WriteLine(BitConverter.ToString(input));
}
}
}
}
After Running my Code, the system logs 00. The characterUUID for battery level (0x2A19, from https://www.bluetooth.com/specifications/gatt/viewer?attributeXmlFile=org.bluetooth.characteristic.battery_level.xml) was read successfully but the value is strange..

ACR122 Device Programming sample does not find reader

I'm trying to experiment with the ACR122 card reader on Windows 8 using the Device Programming sample for C# that ships with the SDK. When I start the sample I don't see the card reader in the list of available devices.
I don't think this is a general driver problem because the tools for configuring the reader (precompiled binaries) list the reader and allow to connecting to it.
I'm new to C# and .NET. I would be glad if anyone could give me some advice on determining what's wrong. If you need more information I will happily provide you with it.

I'm no expert either, I'm currently working with the ACR122U reader and the samples didn't work perfectly for me either. But, I was able to write a little C# program so i can read/write small amounts of text (converted to hexadecimal) onto a Smart Card.
So I suggest you try to write it yourself, like I did, I'll give you some code which got me started (I used the pcsc-sharp dll):
using PCSC;
namespace SmartcardCheck
{
class Program
{
static void Main(string[] args)
{
using (var context = new SCardContext())
{
context.Establish(SCardScope.System);
string[] readerNames = null;
try
{
// retrieve all reader names
readerNames = context.GetReaders();
// get the card status of each reader that is currently connected
foreach (var readerName in readerNames)
{
using (var reader = new SCardReader(context))
{
Console.WriteLine("Trying to connect to reader {0}.", readerName);
var sc = reader.Connect(readerName, SCardShareMode.Shared, SCardProtocol.Any);
if (sc == SCardError.Success)
{
DisplayReaderStatus(reader);
}
else
{
Console.WriteLine("No card inserted or reader is reserved exclusively by another application.");
Console.WriteLine("Error message: {0}\n", SCardHelper.StringifyError(sc));
}
}
}
}
catch (Exception)
{
if (readerNames == null)
{
Console.WriteLine("No readers found.");
return;
}
}
Console.ReadKey();
}
}
}
}
Hope it helps you :)

The ACR122 is not seen by Windows as an NFC (proximity) device, it is a smart card device which has the capability to read NFC cards. To use it within Modern Apps or via the WinRT API's you'll actually need to use Windows 8.1 which has introduced support for smart cards.

MonoDroid Bluetooth

I have been working with Monodroid for a few days and still can't figure out how to send a command through Bluetooth.
This is my scenario: I have a Tablet/Cellphone working with Android 2.1+ and need to send and receive data to a Bluetooth printer (in bytes).
What i managed so far:
using Android.Bluetooth; // library necessary
BluetoothAdapter bth = BluetoothAdapter.DefaultAdapter;
if (!bth.IsEnabled)
bth.Enable();
ICollection<BluetoothDevice> bthD = bth.BondedDevices;
foreach (BluetoothDevice d in bthD)
{
if (d.Name == "DPP-350")
{
Java.Util.UUID UUID = Java.Util.UUID.FromString("00001101-0000-1000-8000-00805F9B34FB");
// Get the BLuetoothDevice object
BluetoothSocket s = d.CreateRfcommSocketToServiceRecord(UUID);
s.Connect();
// Try to send command
...
s.Close()
}
}
The program asks for the pairing info, with is done correctly.
I have tried many ways to send the command:
// the command
// Self_Test = Chr(27) + Chr(84) = ESC T
byte[] dBytes = System.Text.Encoding.GetEncoding(1252).GetBytes(Self_Test);
// wont work
new Java.IO.ObjectOutputStream(s.OutputStream).Write(dBytes);
// wont work
System.IO.Stream st = s.OutputStream;
if (st.CanWrite)
{
st.Write(dBytes, 0, dBytes.Length);
st.Flush();
}
// wonk work
s.OutputStream.Write(dBytes, 0, dBytes.Length);
s.OutputStream.Flush();
No error is raised. I'm running out of options here...
Thanks in advance!

I know this is a very old thread, but I wanted to post a reply so others will know the answer. I too searched hard with no luck.
s.OutputStream.BeginWrite(buffer, 0, buffer.Length,new AsyncCallback(delegate {}), State.Connected);
Thanks.