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• Why does my Blink based browser play hide and seek ?

  21 janvier 2016, par Caius Jard

  We have a C# tool (that I wrote) that records online broadcasts taking place a custom written (that we wrote) flash app. (There are no DRM or copyright issues here.)

  We’ve coded up a system whereby this tool is installed on a Windows Server 2012 R2 Amazon AWS instance. After we boot the instance, the tool loads, waits for the right time to start recording, launches a browser and passes the command line argument of the URL to access the broadcast. The browser will then load the flash app and the interview audio and video will start arriving at the browser instance on AWS

  By way of a virtual audio cable driver, screen / audio capture directshow filters and ffmpeg a screen recording is taken. The C# tool calls ffmpeg and ffmpeg will record the screen reliably for the entire interview, then the tool shuts the whole thing down

  The problem I’m having is that both Chrome and Electron browser sometimes simply don’t draw themselves on the screen so all ffmpeg ends up recording is a blank desktop and the audio of the broadcast (hence, the browser IS running)

  We found this out when recordings started turning up with X hours of merely recording the windows desktop and the tool’s main window with a countdown timer.

  A screenshotting facility was built into the tool and added to its web control interface, and this way we can test whether the browser is visible - a human looks at the screenshot of every broadcast, just after recording has started (the browser is supposed to be on show by this time)

  We notice that 50% of the time, the browser isn’t drawing itself on screen. By 50% I mean that every other recording that the AWS instance carries out, will be blank : AWS starts, records ok, shuts down. AWS starts again an hour later for a different broadcast, recording is blank, shuts down.. Starts/ok/shutdown. Starts/blank/shutdown. Repeat ad infinitum

  What’s even more strange is that if I run VNCviewer on my dev machine and connect up to an instance that is having a problem, the instant that the VNC connection is up and the remote desktop is showing on my screen, the browser suddenly appears as if nothing was ever wrong. A screenshot from before the VNC connect shows blank desktop, connect VNC, take another screenshot and the browser is there. All through it the audio is fine - the browser connected to the boadcast is fine, for sure

  It’s as though Chrome/Electron thinks "you know what, noone is looking at me so I’m not going to bother drawing myself". No screen saver is set, though the power plan has the setting "turn off the display after 15 minutes".

  Perhaps Chrome/Electron have a test amounts to "if the display is off, don’t draw". I can’t explain the inconsistency though - the recorder launches at least 1 hour before it’s needed, and sits there idle until it’s time to start the browser. You’d hence imagine that the "power off the monitor after 15 mins" setting would reliably have ensured the "monitor" is "off" by the time every recording start comes around

  This behaviour doesn’t happen with any of the other browsers (but unfortunately the app doesn’t and cannot work in them because it uses some weird chrome-only technology/API).

  Can anyone suggest anything to look at to help debug this, or anything I can build into the C# tool to overcome the problem ? Coding it up to connect to itself via VNC for a few seconds after it has launched the browser.. Well that just tastes nasty.

  Naturally, as soon as I connect to the machine via VNC (rather than RDP - RDP isn’t usable because the recording context is in a logged on session for a particular user) the problem goes away, which makes it frustratingly hard to debug.

• Decoding a h264 (High) stream with OpenCV's ffmpeg on Ubuntu

  9 janvier 2017, par arvids

  I am working with a video stream (no audio) from an ip camera on Ubuntu 14.04. Also i am a beginner with Ubuntu and everything on it. Everything was going great with a camera that has these parameters (from FFMPEG) :

  Input #0, rtsp, from 'rtsp://*private*:8900/live.sdp': 0B f=0/0   
  
    Metadata:
  
      title           : RTSP server
  
      Stream #0:0: Video: h264 (Main), yuv420p(progressive), 352x192, 29.97 tbr, 90k tbn, 180k tbc

  But then i changed to a newer camera, which has these parameters :

  Input #0, rtsp, from 'rtsp://*private*/media/video2':0B f=0/0   
  
    Metadata:
  
      title           : VCP IPC Realtime stream
  
      Stream #0:0: Video: h264 (High), yuvj420p(pc, bt709, progressive), 1280x720, 25 fps, 25 tbr, 90k tbn, 50 tbc

  My C++ program uses OpenCV3 to process the stream. By default OpenCV uses ffmpeg to decode and display the stream with function VideoCapture.

  VideoCapture vc;
  
  vc.open(input_stream);
  
  while ((vc >> frame), !frame.empty()) {
  
     *do work*
  
  }

  With the new camera stream i get errors like these (from ffmpeg) :

  [h264 @ 0x7c6980] cabac decode of qscale diff failed at 41 38
  
  [h264 @ 0x7c6980] error while decoding MB 41 38, bytestream (3572)
  
  [h264 @ 0x7c6980] left block unavailable for requested intra mode at 0 44
  
  [h264 @ 0x7c6980] error while decoding MB 0 44, bytestream (4933)
  
  [h264 @ 0x7bc2c0] SEI type 25 truncated at 208
  
  [h264 @ 0x7bfaa0] SEI type 25 truncated at 206
  
  [h264 @ 0x7c6980] left block unavailable for requested intra mode at 0 18
  
  [h264 @ 0x7c6980] error while decoding MB 0 18, bytestream (14717)

  The image sometimes is glitched, sometimes completely frozen. After a few seconds to a few minutes the stream freezes completely without an error. However on vlc it plays perfectly. I installed the newest version (3.2.2) of ffmpeg player with

  ./configure --enable-gpl --enable-libx264

  Now playing directly with ffplay (instead of launching from source code with OpenCV function VideoCapture), the stream plays better, doesn’t freeze, but sometimes still displays warnings :

  [NULL @ 0x7f834c008c00] SEI type 25 size 896 truncated at 320=1/1   
  
  [h264 @ 0x7f834c0d5d20] SEI type 25 size 896 truncated at 319=1/1   
  
  [rtsp @ 0x7f834c0008c0] max delay reached. need to consume packet   
  
  [rtsp @ 0x7f834c0008c0] RTP: missed 1 packets
  
  [h264 @ 0x7f834c094740] concealing 675 DC, 675 AC, 675 MV errors in P frame
  
  [NULL @ 0x7f834c008c00] SEI type 25 size 896 truncated at 320=1/1  

  Changing the camera hardware is not an option. The camera can be set to encode to h265 or mjpeg. When encoding to mjpeg it can output 5 fps, which is not enough. Decoding to a static video is not an option either, because i need to display real time results about the stream. Here is a list of API backends that can be used in function VideoCapture. Maybe i should swithc to some other decoder and player ?
  From my research i conclude that i have these options :

  • Somehow get OpenCV to use the ffmpeg player from another directory, where it is compiled with libx264

  • Somehow get OpenCV to use libVlc instead of ffmpeg

  One example of switching to vlc is here, but i don’t understand it well enough to say if that is what i need. Or maybe i should be parsing the stream in code ? I don’t rule out that this could be some basic problem due to a lack of dependencies, because, as i said, i’m a beginner with Ubuntu.

  • Use vlc to preprocess the stream, as suggested here.

  This is probably slow, which again is bad for real time results.
  Any suggestions and coments will be appreciated.

• Analytics for the Internet of Things : collecting all your things’ data with Piwik to stay in control ?

  25 novembre 2015, par Matthieu Aubry — About

  At Piwik and Piwik PRO, our mission is to create the leading free and open source analytics platform, and supporting global organisations and communities to keep full control over their data.

  Our broad mission started 8 years ago and we focused at first helping people to liberate their website analytics data, then liberate their mobile app analytics data. But it is clear that there is much more than Web + Mobile : data is everywhere and a lot more data is being generated by software, people and their activities, robots, sensors…

  I’d like to share an interesting article which highlights one of the growing trends of technology : the rise of the Internet Of Things : 6 Ways Analytics And The Internet Of Things Will Transform Business.

  Here is an extract :

  The tech industry is no stranger to change, but the data derived from the IoT is taking disruption to a new level.

  At IBM’s Insight conference last month, Bob Picciano, senior vice president of IBM Analytics, talked about the rise of the “cognitive business”, or an enterprise that engages with analytics to improve its customer relations, business processes, and decision-making capabilities.

  There are dueling predictions over how ubiquitous the Internet of Things will be, but most indicate that the marketplace will host between 50 and 75 billion connected objects by 2020, signaling novel challenges for hardware manufacturing and development. Software engineers, likewise, may need to completely revamp programs to better exploit the influx of data, while innovators need to wrestle with the changes wrought by analytics.

  IBM’s Insight event unfolded in light of this wave of disruption. The lineup of corporate presenters converged on the same message : Analytics is for everyone, and your viability in the marketplace depends on it.

  […]

  IBM’s Insight 2015 conference sounded off on the most important trends in data usage and management. It also served a wake-up call for developers, engineers, and tech leaders. As the Internet of Things alters the landscape of analytics, hardware design needs to change, software development requires novel approaches, and tech management must become more agile in order to realize data’s greatest benefits.

  So far there are 1 million websites using Piwik… but what if there could be 10 or 50 million things (sensors, devices) being measured by Piwik ?

  Together we will be creating the best open source and generic analytics platform, that is engineered to last, and designed to help humanity keep control and gain Freedom.

  We aim for Piwik to be the ideal platform to measure the Internet Of Things.

  We’re still at the beginning of this journey and it will take the best of all of us to get there.

  See you on the way !

  PS : if you’d like to get involved with Piwik, we would be glad to welcome you !