How is TeamViewer so fast

Question

Sorry about the length  it s kinda necessary   Introduction  I m developing a remote desktop software  just for fun  in C  4 0 for Windows Vista 7  I ve gotten through basic obstacles  I have a robust UDP messaging system  relatively clean program design  I ve got a mirror driver  the free DFMirage mirror driver from DemoForge  up and running  and I ve implemented NAT traversal for all NAT types except Symmetric NATs  present in corporate firewall situations    Regarding screen transfer sharing  thanks to the mirror driver  I m automatically notified of changed screen regions and I can simply marshal the mirror driver s ever-changing screen bitmap to my own bitmap  Then I compress the screen region as a PNG and send it off from the server to my client  Things are looking pretty good  but it s not fast enough  It s just as slow as VNC  btw  I don t use the VNC protocol  just a custom amateur protocol    From the slowest remote desktop software to the fastest  the list usually begins at all VNC-like implementations  then climbs up to Microsoft Windows Remote Desktop   and then   TeamViewer  Not quite sure about CrossLoop  LogMeIn - I haven t used them  but TeamViewer is insanely fast  It s quite literally live  I ran a tree command on Command Prompt and it updated with 20 ms delay  I can browse the web just a few milliseconds slower than on my laptop  Scrolling code vertically in Visual Studio has 50 ms lag time  Think about how robust TeamViewer s screen-transfer solution must be to accomplish all this   VNCs use poll-based hooks for detecting screen change and brute force screen capturing comparing at their worst  At their best  they use a mirror driver like DFMirage  I m at this level  And they use something called the RFB protocol   Microsoft Windows Remote Desktop apparently goes one step higher than VNC  I heard  from somewhere on StackOverflow  that Windows Remote Desktop doesn t send screen bitmaps  but actual drawing commands  That s quite brilliant  because it can just send simple text  draw this rectangle at this coordinate and color it with this gradient   Remote Desktop really is pretty fast - and it s the standard way of working from home  And it uses something called the RDP protocol   Now TeamViewer is a complete mystery to me  Apparently  they released their source code for Version 2  TeamViewer is Version 7 as of February 2012   People have read it and said that Version 2 is useless - that it s just a few improvements over VNC with automatic NAT traversal    But Version 7   it s ridiculously fast now  I mean  it s actually faster than Windows Remote Desktop  I ve streamed DirectX 3D games with TeamViewer  at 1 fps  but Windows Remote Desktop doesn t even allow DirectX to run    By the way  TeamViewer does all this without a mirror driver  There is an option to install one  and it gets just a bit faster   The Question  My question is  how is TeamViewer so fast  It must not be possible  If you ve got 1920 by 1080 resolution at even 24 bit depth  16 bit depth would be noticeably ugly   thats still 6 220 800 bytes raw  Even using libjpeg-turbo  one of the fastest JPG compression libraries used by large corporations   compressing it down to 30KB  let s be extremely generous   would take time to route through TeamViewer s servers  TeamViewer bypasses corporate Symmetric NATs by simply proxying traffic through their servers   And that libjpeg-turbo compression would take time to compress  High-quality JPG compression takes 175 milliseconds for a full 1920 by 1080 screenshot for me  And that number goes up if the host s computer runs an Atom processor  I simply don t understand how TeamViewer has optimized their screen transfer so well  Again  small-size images might be highly compressed  but take at least tens of milliseconds to compress  Large-size images take no time to compress  but take a long time to get through  Somehow  TeamViewer completes this entire process to get roughly 20-25 frames per second  I ve used a network monitor  and TeamViewer is still lagless at speeds of 500 Kbps and 1 Mbps  VNC software lag for a few seconds at that transfer rate   During my tree Command Prompt test  TeamViewer was receiving inbound data at a rate of 1 Mbps and still running 5-6 fps  VNC and remote desktop don t do that  So  how   The answers will be somewhat complicated and intricate  so please don t post your  0 02 if you re only going to say it s because they use UDP instead of TCP  would you believe they actually do use TCP just as successfully though    I m hoping there s a TeamViewer developer somewhere here on StackOverflow   Potential Answers  Will update this once people reply    My thoughts are  first of all  that TeamViewer has very fine network control  For example  they split large packets to just under the MTU size and never waste a trip  They probably have all sorts of fancy hooks to detect screen changes along with extremely fast XOR image comparisons

User · Answer

It sounds indeed like video streaming more than image streaming, as someone suggested. JPEG/PNG compression isn't targeted for these types of speeds, so forget them.

Imagine having a recording codec on your system that can realtime record an incoming video stream (your screen). A bit like Fraps perhaps. Then imagine a video playback codec on the other side (the remote client). As HD recorders can do it (record live and even playback live from the same HD), so should you, in the end. The HD surely can't deliver images quicker than you can read your display, so that isn't the bottleneck. The bottleneck are the video codecs. You'll find the encoder much more of a problem than the decoder, as all decoders are mostly free.

I'm not saying it's simple; I myself have used DirectShow to encode a video file, and it's not realtime by far. But given the right codec I'm convinced it can work.

User · Answer

would take time to route through TeamViewer s servers  TeamViewer bypasses corporate Symmetric NATs by simply proxying traffic through their servers    You ll find that TeamViewer rarely needs to relay traffic through their own servers  TeamViewer penetrates NAT and networks complicated by NAT using NAT traversal  I think it is UDP hole-punching  like Google s libjingle     They do use their own servers to middle-man in order to do the handshake and connection set-up  but most of the time the relationship between client and server will be P2P  best case  when the hand-shake is successful    If NAT traversal fails  then TeamViewer will indeed relay traffic through its own servers    I ve only ever seen it do this when a client has been behind double-NAT  though

User · Answer

Oddly  but in my experience TeamViewer is not faster more responsive than VNC  only easier to setup  I have a couple of win-boxen that I VNC over OpenVPN into  so there is another overhead layer  and that s on cheap Cable  512 up  and I find properly setup TightVNC to be much more responsive than TeamViewer to same boxen  RDP  naturally  even more so since by large part it sends GUI draw commands instead of bitmap tiles   Which brings us to    Why are you not using VNC  There are plethora of open source solutions  and Tight is probably on top of it s game right now  Advanced VNC implementations use lossy compression and that seems to achieve  better results than your choice of PNG  Also  IIRC the rest of the payload is also  squashed using zlib  Bothj Tight and UltraVNC have very optimized algos  especially for windows  On top of that Tight is open-source  If win boxen are your primary target RDP may be a better option  and has an opensource implementation  rdesktop  If  nix boxen are your primary target NX may be a better option and has an open source implementation  FreeNX  albeit not as optimised as NoMachine s proprietary product     If compressing JPEG is a performance issue for your algo  I m pretty sure that image comparison would still take away some performance  I d bet they use best-case compression for every specific situation ie lossy for large frames  some quick and dirty internall losless for smaller ones  compare bits of images and send only diffs of sort and bunch of other optimisation tricks   And a lot of those tricks must be present in Tight   2 0 since again  in my experience it beats the hell out of TeamViewer performance wyse  YMMV   Also the choice of a JIT compiled runtime over something like C   might take a slice from your performance edge  especially in memory constrained machines  a lot of performance tuning goes to the toilet when windows start using the pagefile intensively   And you will need memory to keep previous image states for internal comparison atop of what DF mirage gives you

User · Answer

The most fundamental thing here probably is that you don t want to transmit static images but only changes to the images  which essentially is analogous to video stream   My best guess is some very efficient  and heavily specialized and optimized  motion compensation algorithm  because most of the actual change in generic desktop usage is linear movement of elements  scrolling text  moving windows  etc  opposed to transformation of elements    The DirectX 3D performance of 1 FPS seems to confirm my guess to some extent

User · Answer

My random guess is  TV uses x264 codec which has a commercial license  otherwise TeamViewer would have to release their source code   At some point  more than 5 years ago   I recall main developer of x264 wrote an article about improvements he made for low delay encoding  if you delay by a few frames encoders can compress better   plus he mentioned some other improvements that were relevant for TeamViewer-like use  In that post he mentioned playing quake over video stream with no noticeable issues  Back then I was kind of sure who was the sponsor of these improvements  as TeamViewer was pretty much the only option at that time  x264 is an open source implementation of H264 video codec  and it s insanely good implementation  it s the best one  At the same time it s extremely well optimized  Most likely due to extremely good implementation of x264 you get much better results with TV at lower CPU load  AnyDesk and Chrome Remote Desk use libvpx  which isn t as good as x264  optimization and video quality wise    However  I don t think TeamView can beat microsoft s RDP  To me it s the best  however it works between windows PCs or from Mac to Windows only  TV works even from mobiles   Update  article was written in January 2010  so that work was done roughly 10 years ago  Also  I made a mistake  he played call of duty  not quake  When you posted your question  if my guess is correct  TeamViewer had been using that work for 3 years  Read that blog post from web archive  x264  the best low-latency video streaming platform in the world  When I read the article back in 2010  I was sure that the  startup   which has requested not to be named  that the author mentions was TeamViewer

User · Answer

A bit late answer  but I suggest you have a look at a not well known project on codeplex called ConferenceXP     ConferenceXP is an open source research platform that provides simple    flexible  and extensible conferencing and collaboration using   high-bandwidth networks and the advanced multimedia capabilities of   Microsoft Windows  ConferenceXP helps researchers and educators   develop innovative applications and solutions that feature   broadcast-quality audio and video in support of real-time distributed   collaboration and distance learning environments    Full source  it s huge   is provided  It implements the RTP protocol

[performance] How is TeamViewer so fast?

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