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  • Monitor mode 802.11 captures on OSX

    - by Mike A
    I'm trying to determine the difference between capturing 802.11 frames in the following ways on OSX (10.8.5). It's a bit esoteric, but I use "Option 2" to capture frames for later analysis, and am wondering if I'm missing something. Option 1: use "airportd": $sudo /usr/libexec/airportd en0 sniff Option 2: use "airport" followed by tcpdump: sudo /System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/airport --channel= sudo tcpdump -I -P -i en0 -w /tmp/capture.pcap (or alternatvely eliminate the -w and watch packets real-time). From what I can tell: Both commands, according to the wifi icon on OSX, put the interface into 'monitor' mode. Both commands output a pcap file that is readable in both wireshark/tcpdump & Eye PA. Both commands appear to capture management, control and data frames. The rub: Option 1 disconnects you from the network. This is expected, when putting an interface into 'monitor' mode. Option 2 does NOT disconnect you, provided you've set the channel to the same channel your currently connected to. This has a distinct advantage of keeping your connection up while capturing in monitor mode. My question: Option 2 does not seem like it should work, or more specifically, it does not seem like I should be able to remain connected while also capturing frames in monitor mode. On a wired NIC, you can be 'promiscuous' and still send frames, though I didn't think the same was true for wireless NIC. I'm questioning the validity of capturing frames w/ Option 2?

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  • Decoding tcp packets using python

    - by mikip
    Hello I am trying to decode data received over a tcp connection. The packets are small, no more than 100 bytes. However when there is a lot of them I receive some of the the packets joined together. Is there a way to prevent this. I am using python I have tried to separate the packets, my source is below. The packets start with STX byte and end with ETX bytes, the byte following the STX is the packet length, (packet lengths less than 5 are invalid) the checksum is the last bytes before the ETX def decode(data): while True: start = data.find(STX) if start == -1: #no stx in message pkt = '' data = '' break #stx found , next byte is the length pktlen = ord(data[1]) #check message ends in ETX (pktken -1) or checksum invalid if pktlen < 5 or data[pktlen-1] != ETX or checksum_valid(data[start:pktlen]) == False: print "Invalid Pkt" data = data[start+1:] continue else: pkt = data[start:pktlen] data = data[pktlen:] break return data , pkt I use it like this #process reports try: data = sock.recv(256) except: continue else: while data: data, pkt = decode(data) if pkt: process(pkt) Also if there are multiple packets in the data stream, is it best to return the packets as a collection of lists or just return the first packet I am not that familiar with python, only C, is this method OK. Any advice would be most appreciated. Thanks in advance Thanks

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  • error detection/correction/recovery in serial protocols

    - by Jason S
    I have some designing to do for a serial protocol and am running into some questions that I figure must have been considered elsewhere. So I'm wondering if there are some recommendations for best practices in designing serial protocols. (Please either state a fact that is easily verifiable, or cite a reputable source if you make a claim.) General recommendations for websites/books are also welcome. In particular I have to deal with issues like parsing a stream of bytes into packets verifying a packet is correct (easy with a CRC, for instance) identifying reasonable types of errors that can occur (e.g. in a point-to-point serial stream, sporadic single bit errors, and dropped series of bytes, are both likely, but extra phantom bytes are unlikely; whereas with a record stored in flash memory or on a disk drive the types of errors that predominate are different) error correction or recovery (if I detect an error in a packet, can I correct it? If not, can I resync to the boundary of the next packet?) how to make variable-length packets robust to error correction / recovery. Any suggestions?

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  • How frequently IP packets are fragmented at the source host?

    - by Methos
    I know that if IP payload MTU then routers usually fragment the IP packet. Finally all the fragmented packets are assembled at the destination using the fields IP-ID, IP fragment offsets and fragmentation flags. Max length of IP payload is 64K. Thus its very plausible for L4 to hand over payload which is 64K. If the L2 protocol is Ethernet, which often is the case, then the MTU will be about 1600 bytes. Hence IP packet will be fragmented at the source host itself. However, a quick search about IP implementation in Linux tells me that in recent kernels, L4 protocols are fragment friendly i.e. they try to save the fragmentation work for IP by handing over buffers of size which is close to MTU. Considering these two facts, I am wondering about how frequently does the IP packet gets fragmented at the source host itself. Does it occur sometimes/rarely/never? Does anyone know if there are exceptions to the rule of fragmentation in linux kernel (i.e. are there situations where L4 protocols are not fragment friendly)? How is this handled in other common OSes like windows? In general how frequently IP packets are fragmented?

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  • How to synchronize Silverlight clients with WCF?

    - by user564226
    Hi, this is probably only some conceptual problem, but I cannot seem to find the ideal solution. I'd like to create a Silverlight client application that uses WCF to control a third party application via some self written webservice. If there is more than one Silverlight client, all clients should be synchronized, i.e. parameter changes from one client should be propagated to all clients. I set up a very simple Silverlight GUI that manipulates parameters which are passed to the server (class inherits INotifyPropertyChanged): public double Height { get { return frameworkElement.Height; } set { if (frameworkElement.Height != value) { frameworkElement.Height = value; OnPropertyChanged("Height", value); } } } OnPropertyChanged is responsible for transferring data. The WCF service (duplex net.tcp) maintains a list of all clients and as soon as it receives a data packet (XElement with parameter change description) it forwards this very packet to all clients but the one the packet was received from. The client receives the package, but now I'm not sure, what's the best way to set the property internally. If I use "Height" (see above) a new change message would be generated and sent to all other clients a.s.o. Maybe I could use the data field (frameworkElement.Height) itself or a function - but I'm not sure whether there would arise problems with data binding later on. Also I don't want to simply copy parts of the code properties, to prevent bugs with redundant code. So what would you recommend? Thanks!

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  • Best practices for encrypting continuous/small UDP data

    - by temp
    Hello everyone, I am having an application where I have to send several small data per second through the network using UDP. The application need to send the data in real-time (no waiting). I want to encrypt these data and insure that what I am doing is as secure as possible. Since I am using UDP, there is no way to use SSL/TLS, so I have to encrypt each packet alone since the protocol is connectionless/unreliable/unregulated. Right now, I am using a 128-bit key derived from a passphrase from the user, and AES in CBC mode (PBE using AES-CBC). I decided to use a random salt with the passphrase to derive the 128-bit key (prevent dictionary attack on the passphrase), and of course use IVs (to prevent statistical analysis for packets). However I am concerned about few things: Each packet contains small amount of data (like a couple of integer values per packet) which will make the encrypted packets vulnerable to known-plaintext attacks (which will result in making it easier to crack the key). Also, since the encryption key is derived from a passphrase, this will make the key space way less (I know the salt will help, but I have to send the salt through the network once and anyone can get it). Given these two things, anyone can sniff and store the sent data, and try to crack the key. Although this process might take some time, once the key is cracked all the stored data will be decrypted, which will be a real problem for my application. So my question is, what is the best practices for sending/encrypting continuous small data using a connectionless protocol (UDP)? Is my way the best way to do it? ...flowed? ...Overkill? ... Please note that I am not asking for a 100% secure solution, as there is no such thing. Cheers

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  • Is this the right way to write a ProtocolDecoder in MINA?

    - by phpscriptcoder
    public class CustomProtocolDecoder extends CumulativeProtocolDecoder{ byte currentCmd = -1; int currentSize = -1; boolean isFirst = false; @Override protected boolean doDecode(IoSession is, ByteBuffer bb, ProtocolDecoderOutput pdo) throws Exception { if(currentCmd == -1) { currentCmd = bb.get(); currentSize = Packet.getSize(currentCmd); isFirst = true; } while(bb.remaining() > 0) { if(!isFirst) { currentCmd = bb.get(); currentSize = Packet.getSize(currentCmd); } else isFirst = false; //System.err.println(currentCmd + " " + bb.remaining() + " " + currentSize); if(bb.remaining() >= currentSize - 1) { Packet p = PacketDecoder.decodePacket(bb, currentCmd); pdo.write(p); } else { bb.flip(); return false; } } if(bb.remaining() == 0) return true; else return false; } } Anyone see anything wrong with this code? When a lot of packets are received at once, even when only one client is connected, one of them might get cut off at the end (12 bytes instead of 15 bytes, for example) which is obviously bad.

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  • Best practices for encrytping continuous/small UDP data

    - by temp
    Hello everyone, I am having an application where I have to send several small data per second through the network using UDP. The application need to send the data in real-time (on waiting). I want to encrypt these data and insure that what I am doing is as secure as possible. Since I am using UDP, there is no way to use SSL/TLS, so I have to encrypt each packet alone since the protocol is connectionless/unreliable/unregulated. Right now, I am using a 128-bit key derived from a passphrase from the user, and AES in CBC mode (PBE using AES-CBC). I decided to use a random salt with the passphrase to derive the 128-bit key (prevent dictionary attack on the passphrase), and of course use IVs (to prevent statistical analysis for packets). However I am concerned about few things: Each packet contains small amount of data (like a couple of integer values per packet) which will make the encrypted packets vulnerable to known-plaintext attacks (which will result in making it easier to crack the key). Also, since the encryption key is derived from a passphrase, this will make the key space way less (I know the salt will help, but I have to send the salt through the network once and anyone can get it). Given these two things, anyone can sniff and store the sent data, and try to crack the key. Although this process might take some time, once the key is cracked all the stored data will be decrypted, which will be a real problem for my application. So my question is, what is the best practices for sending/encrypting continuous small data using a connectionless protocol (UDP)? Is my way the best way to do it? ...flowed? ...Overkill? ... Please note that I am not asking for a 100% secure solution, as there is no such thing. Cheers

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  • UDP packets are dropped when its size is less than 12 byte in a certain PC. how do i figure it out the reason?

    - by waan
    Hi. i've stuck in a problem that is never heard about before. i'm making an online game which uses UDP packets in a certain character action. after i developed the udp module, it seems to work fine. though most of our team members have no problem, but a man, who is my boss, told me something is wrong for that module. i have investigated the problem, and finally i found the fact that... on his PC, if udp packet size is less than 12, the packet is never have been delivered to the other host. the following is some additional information: 1~11 bytes udp packets are dropped, 12 bytes and over 12 bytes packets are OK. O/S: Microsoft Windows Vista Business NIC: Attansic L1 Gigabit Ethernet 10/100/1000Base-T Controller WSASendTo returns TRUE. loopback udp packet works fine. how do you think of this problem? and what do you think... what causes this problem? what should i do for the next step for the cause? PS. i don't want to padding which makes length of all the packets up to 12 bytes.

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  • Java if/else behaving strangely

    - by Alex
    I'm a real newbie to java, so please excuse me if this is a hopelessly straightforward problem. I have the following from my java game server: // Get input from the client DataInputStream in = new DataInputStream (server.getInputStream()); PrintStream out = new PrintStream(server.getOutputStream()); disconnect=false; while((line = in.readLine().trim()) != null && !line.equals(".") && !line.equals("") && !disconnect) { System.out.println("Received "+line); if(line.equals("h")){ out.println("h"+EOF); // Client handshake System.out.println("Matched 1"); }else if (line.equals("<policy-file-request/>")) { out.println("..."+EOF); // Policy file System.out.println(server.getInetAddress()+": Policy Request"); disconnect=true; System.out.println("Matched 2"); }else if(line.substring(0,3).equals("GET")||line.substring(0,4).equals("POST")){ out.println("HTTP/1.0 200 OK\nServer: VirtuaRoom v0.9\nContent-Type: text/html\n\n..."); // HTML status page disconnect=true; System.out.println("Matched 3"); } else { System.out.println(server.getInetAddress()+": Unknown command, client disconnected."); disconnect=true; System.out.println("Matched else"); } } server.close(); First of all, the client sends an "h" packet, and expects the same back (handshake). However, I want it to disconnect the client when an unrecognised packet is received. For some reason, it responds fine to the handshake and HTML status request, but the else clause is never executed when there's an unknown packet. Thanks

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  • [java] tcp socket communication [send and recieve help]

    - by raven
    hello, I am creating a Chat in java. I have a method (onMouseRelease) inside an object that creates a tcp server and waits for a socket ServerSocket server = new ServerSocket(port); Socket channel = server.accept(); now I want to make a thread that will loop and read data from the socket, so that once the user on the other side sent me a string, I will extract the data from the socket [or is it called packet? sry I am new to this], and update a textbox to add the additional string from the socket [or packet?]. I have no idea how to READ (extract) the information from the scoket [/packet] and then update it into a JTextArea which is called userOutput. And how to Send a string to the other client, so that it will also could read the new data and update its JTextArea. (from what I know, for a 2 sided tcp communication you need one computer to host a server and the other to connect [as a client] and once the connection is set the client can also recieve new information from the socket. Is that true? and please tell me how ) Any help appreciated !! I know this is abit long but I have searched allot and didn't understand [I saw something like printwriter but failed to understand].

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  • TCP socket communication

    - by raven
    hello, I am creating a Chat in java. I have a method (onMouseRelease) inside an object that creates a tcp server and waits for a socket like this: ServerSocket server = new ServerSocket(port); Socket channel = server.accept(); Now I want to make a thread that will loop and read data from the socket, so that once the user on the other side sends me a string, I will extract the data from the socket (or is it called packet? Sorry, I am new to this) and update a textbox to add the additional string from the socket (or packet?). I have no idea how to READ (extract) the information from the socket(/packet) and then update it into a JTextArea which is called userOutput. And how to send a string to the other client, so that it will also could read the new data and update its JTextArea. From what I know, for a 2 sided TCP communication you need one computer to host a server and the other to connect (as a client) and once the connection is set the client can also receive new information from the socket. Is that true? and please tell me how. Any help is appreciated! I know this is a bit long but I have searched a lot and didn't understand it (I saw something like PrintWriter but failed to understand).

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  • Java: GatheringByteChannel advantages?

    - by Jason S
    I'm wondering when the GatheringByteChannel's write methods (taking in an array of ByteBuffers) have advantages over the "regular" WritableByteChannel write methods. I tried a test where I could use the regular vs. the gathering write method on a FileChannel, with approx 400KB/sec total in ByteBuffers of between 23-27 bytes in length in both cases. Gathering writes used an array of 64. The regular method used up approx 12% of my CPU, and the gathering method used up approx 16% of my CPU (worse than the regular method!) This tells me it's NOT useful to use gathering writes on a FileChannel around this range of operating parameters. Why would this be the case, and when would you ever use GatheringByteChannel? (on network I/O?) Relevant differences here: public void log(Queue<Packet> packets) throws IOException { if (this.gather) { int Nbuf = 64; ByteBuffer[] bbufs = new ByteBuffer[Nbuf]; int i = 0; Packet p; while ((p = packets.poll()) != null) { bbufs[i++] = p.getBuffer(); if (i == Nbuf) { this.fc.write(bbufs); i = 0; } } if (i > 0) { this.fc.write(bbufs, 0, i); } } else { Packet p; while ((p = packets.poll()) != null) { this.fc.write(p.getBuffer()); } } }

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  • WebBrowser DrawToBitmap other methods?

    - by Matt
    I am trying to capture the content of the WebBrowser control. DrawToBitmap() would work perfectly, but it is not supported in documentation for the WebBrowser control. I have been trying to find another way to capture the contents of the WebBrowser control and save them to a local image file. Anyone have any workarounds or other methods to save the contents of the WebBrowser control to a local image file?

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  • how to set mediatype for prreview pin vc++ directshow

    - by Sathis
    hai.. am writing simple appliaction for capture and rendering video in vc++ .and i set meadiatype for capture pin RGB24 AND 640*480 image size. Image is captured thats size.but i cant rendering preview.if i render that i get BLACk PREVIEW only.i checked also in GRAPH EDIT tool.but i cant get. am using wcsa400 card type cam and .net 2005 pl kindly help me.

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  • convert file path to string

    - by salvationishere
    I am developing a c# web application with VS 2008 where I am trying to capture the physical path of the selected file. Using IE, I am finally able to retrieve this now in text variable. But I want to capture this information in string. How do I do this? Currently I am using: lb3.Text = Page.Request.PhysicalPath; And it gives me: Text = "C:\Documents and Settings\Admin\My Documents\Visual Studio 2008\Projects\AddFileToSQL\AddFileToSQL\Default.aspx"

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  • Can I get a bitmap of an arbitrary window in another application process?

    - by Chris Farmer
    I am trying to automate a third-party Win32 application where I want to capture the graphics content of a particular window at defined time intervals. I am in the early phases of this, and I'm currently trying to use the Microsoft UI Automation API via C# to do most of the interaction between my client app and the external app. I can now get the external app to do what I want it to do, but now I want to capture the graphics from a specific window that seems to be some third-party owner-drawn control. How can I do this? The window I want to capture is the one marked by the red rectangle in this image: I have an implementation that sort of works, but it's dependent on the external app's UI being on top, and that's not guaranteed for me, so I'd prefer to find something more general. var p = Process.Start("c:\myapp.exe"); var mainForm = AutomationElement.FromHandle(p.MainWindowHandle); // "workspace" below is the window whose content I want to capture. var workspace = mainForm.FindFirst(TreeScope.Descendents, new PropertyCondition(AutomationElement.ClassNameProperty, "AfxFrameOrView70u")); var rect = (Rect) workspace.GetCurrentPropertyValue(AutomationElement.BoundingRectangleProperty); using (var bmp = new Bitmap((int)rect.Width, (int)rect.Height)) { using (var g = Graphics.FromImage(bmp)) { g.CopyFromScreen((int)rect.Left, (int)rect.Top, 0, 0, new Size((int)rect.Width, (int)rect.Height)); bmp.Save(@"c:\screenshot.png", ImageFormat.Png); } } The above works well enough when the automated app is on top, but it just blindly copies the screen in the rectangle, so my code is at the mercy of whatever happens to be running on the machine and might cover my app's window. I have read some suggestions to send the WM_PRINT message to the window. This question/answer from a few months back seemed promising, but when I use this code, I just get a white rectangle with none of my control's actual contents. var prop = (int)workspace.GetCurrentPropertyValue(AutomationElement.NativeWindowHandleProperty); var hwnd = new IntPtr(prop); using ( var bmp2 = new Bitmap((int)rect.Width, (int)rect.Height)) { using (Graphics g = Graphics.FromImage(bmp2)) { g.FillRectangle(SystemBrushes.Control, 0, 0, (int)rect.Width, (int)rect.Height); try { SendMessage(hwnd, WM_PRINT, g.GetHdc().ToInt32(), (int)(DrawingOptions.PRF_CHILDREN | DrawingOptions.PRF_CLIENT | DrawingOptions.PRF_OWNED)); } finally { g.ReleaseHdc(); } bmp2.Save(@"c:\screenshot.bmp"); } } So, first, is it even possible for me to reliably save a bitmap of a window's contents? If so, what is the best way, and what is wrong with my WM_PRINT with SendMessage attempt?

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  • Capturing Ctrl-Alt-Del in JavaScript/jQuery

    - by AJ
    While just playing with jQuery/JavaScript I ran across this problem. I could capture Alt and Ctrl keys but NOT Del and certainly not all of them together. $(document).ready(function() { $("#target").keydown(function(event) { if (event.ctrlKey && event.altKey && event.keyCode == '46') { alter("Ctrl-Alt-Del combination"); } }); }); Is it possible to capture all these three keys together?

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  • How restore data from pcap file?

    - by dscTobi
    Hi ppl =) I have following file: test_network.pcap: tcpdump capture file (little-endian) - version 2.4 (Ethernet, capture length 65535) I know that in this file are few video streams and i need to extract them. How can i do this? The biggest problem is that size of file ~180 GB ))

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  • save button error in AS project

    - by Rajeev
    Whats wrong with the following code,There is an error at saveButton.visible = false; discardButton.visible = false; package { import flash.display.Sprite; import flash.media.Camera; import flash.media.Video; import flash.display.BitmapData; import flash.display.Bitmap; import flash.events.MouseEvent; import flash.net.FileReference; import flash.utils.ByteArray; import com.adobe.images.JPGEncoder; public class caml extends Sprite { private var camera:Camera = Camera.getCamera(); private var video:Video = new Video(); private var bmd:BitmapData = new BitmapData(320,240); private var bmp:Bitmap; private var fileReference:FileReference = new FileReference(); private var byteArray:ByteArray; private var jpg:JPGEncoder = new JPGEncoder(); public function caml() { saveButton.visible = false; discardButton.visible = false; saveButton.addEventListener(MouseEvent.MOUSE_UP, saveImage); discardButton.addEventListener(MouseEvent.MOUSE_UP, discard); capture.addEventListener(MouseEvent.MOUSE_UP, captureImage); if (camera != null) { video.smoothing = true; video.attachCamera(camera); video.x = 140; video.y = 40; addChild(video); } else { trace("No Camera Detected"); } } private function captureImage(e:MouseEvent):void { bmd.draw(video); bmp = new Bitmap(bmd); bmp.x = 140; bmp.y = 40; addChild(bmp); capture.visible = false; saveButton.visible = true; discardButton.visible = true; } private function saveImage(e:MouseEvent):void { byteArray = jpg.encode(bmd); fileReference.save(byteArray, "Image.jpg"); removeChild(bmp); saveButton.visible = false; discardButton.visible = false; capture.visible = true; } private function discard(e:MouseEvent):void { removeChild(bmp); saveButton.visible = false; discardButton.visible = false; capture.visible = true; } } }

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  • c# change global cursor

    - by andySF
    Hi, it is possible to change global mouse cursor from c#? the thing is i use a global hook shortcut key to capture a window like spywindow and i want to change mouse cursor globally when i select my handle and restore it when i click left mouse. Another question is about the click itself. When I'm in capture mode can i take click just for my purpose?it will be nice if i didn't press stuff on screen when i select my window!. Thanks!

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  • WinForms: How to prevent textbox from opening alt menu?

    - by Digiku
    I have this textbox I use to capture keyboard shortcuts for a preferences config. I use a low-level keyboard hook to capture keys and also prevent them from taking action, e.g. the Windows key, but the Alt key still comes through and makes my textbox lose focus. How can I block the Alt key, so the focus is kept unaltered at my textbox?

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  • Audio/video streaming on Windows platform

    - by bushtucker
    I'm building an interactive language learning application to be used in a classroom environment. The idea is that a teacher should be able to talk to the students (=audio stream to all students), let students talk to each other (= audio P2P) in groups of two or more, let students watch a video coming from a the DVD player or coming from a media server. It should be possible to save the audio/video streams. The teacher should also be able to monitor, take-over or block the desktop of the students. The platform is Windows and it's a desktop application, no web application. The audio delay should be as minimal as poosible. Optionally a student sitting at home should be supported, but it's not a high priority. I am now finished with the classroom control part of the application (login, monitor, block, ...) and want to start the audio and video part. I've been evaluating several options like DirectX, GStreamer and SIP but now I have to make a decision. DirectX seems an obvious choice for the Windows platform, but it only lets me capture and playback audio and video. The encoding/decoding/network part I should do myself. GStreamer contains all kinds of options to capture/encode/stream/save audio and video streams. I've experimented a bit with it (ossbuild) and it does seem to involve a lot of trial and error to make something work: - microphone capture (via directsoundsrc) produces cracking noises on some computers - rtpL16 payloader didn't work well - streaming raw audio over the network only working at a sampling rate of 8000, no higher - there are a lot of errors when receiving mpeg4 video (bad I-frame), on some computers worse than others It is my impression that gstreamer is primary targetted at linux platforms. Development and support for the Windows platform seems to be a little behind. Nevertheless it's a powerful framework that could save me months and years of work. SIP seems to be able to do everything I want, but it is targeted towards telephony and IM. I don't know how flexible SIP is. It seems to me that the SIP layer would just be overhead as I already have a central (teacher) application that can control and setup all the streams. The interesting parts of frameworks like opalvoip and freeswitch are the actual audio/video capture, the encoding and transmission. Does anyone know how these interesting parts relate a framework like gstreamer? Are they easy to integrate into a custom application? Are they flexible enough? Does anyone have experience with all or one of these technologies? Maybe there are even other options I can look at? Many thanks for your advice

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