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• Use deck.js as a remote presentation tool

  8 janvier 2014, par silvia

  deck.js is one of the new HTML5-based presentation tools. It’s simple to use, in particular for your basic, every-day presentation needs. You can also create more complex slides with animations etc. if you know your HTML and CSS.

  Yesterday at linux.conf.au (LCA), I gave a presentation using deck.js. But I didn’t give it from the lectern in the room in Perth where LCA is being held – instead I gave it from the comfort of my home office at the other end of the country.

  I used my laptop with in-built webcam and my Chrome browser to give this presentation. Beforehand, I had uploaded the presentation to a Web server and shared the link with the organiser of my speaker track, who was on site in Perth and had set up his laptop in the same fashion as myself. His screen was projecting the Chrome tab in which my slides were loaded and he had hooked up the audio output of his laptop to the room speaker system. His camera was pointed at the audience so I could see their reaction.

  I loaded a slide master URL :
  http://html5videoguide.net/presentations/lca_2014_webrtc/?master
  and the room loaded the URL without query string :
  http://html5videoguide.net/presentations/lca_2014_webrtc/.

  Then I gave my talk exactly as I would if I was in the same room. Yes, it felt exactly as though I was there, including nervousness and audience feedback.

  How did we do that ? WebRTC (Web Real-time Communication) to the rescue, of course !

  We used one of the modules of the rtc.io project called rtc-glue to add the video conferencing functionality and the slide navigation to deck.js. It was actually really really simple !

  Here are the few things we added to deck.js to make it work :

  • Code added to index.html to make the video connection work :

    <meta name="rtc-signalhost" content="http://rtc.io/switchboard/">
    
    <meta name="rtc-room" content="lca2014">
    
    ...
    
    <video id="localV" rtc-capture="camera" muted></video>
    
    <video id="peerV" rtc-peer rtc-stream="localV"></video>
    
    ...
    
    <script src="glue.js"></script>
    
    <script>
    
    glue.config.iceServers = [{ url: 'stun:stun.l.google.com:19302' }];
    
    </script>

    The iceServers config is required to punch through firewalls – you may also need a TURN server. Note that you need a signalling server – in our case we used http://rtc.io/switchboard/, which runs the code from rtc-switchboard.

  • Added glue.js library to deck.js :

    Downloaded from https://raw.github.com/rtc-io/rtc-glue/master/dist/glue.js into the source directory of deck.js.

  • Code added to index.html to synchronize slide navigation :

    glue.events.once('connected', function(signaller) {
    
      if (location.search.slice(1) !== '') {
    
        $(document).bind('deck.change', function(evt, from, to) {
    
          signaller.send('/slide', {
    
            idx: to,
    
            sender: signaller.id
    
          });
    
        });
    
      }
    
      signaller.on('slide', function(data) {
    
        console.log('received notification to change to slide: ', data.idx);
    
        $.deck('go', data.idx);
    
      });
    
    });

    This simply registers a callback on the slide master end to send a slide position message to the room end, and a callback on the room end that initiates the slide navigation.

  And that’s it !

  You can find my slide deck on GitHub.

  Feel free to write your own slides in this manner – I would love to have more users of this approach. It should also be fairly simple to extend this to share pointer positions, so you can actually use the mouse pointer to point to things on your slides remotely. Would love to hear your experiences !

  Note that the slides are actually a talk about the rtc.io project, so if you want to find out more about these modules and what other things you can do, read the slide deck or watch the talk when it has been published by LCA.

  Many thanks to Damon Oehlman for his help in getting this working.

  BTW : somebody should really fix that print style sheet for deck.js – I’m only ever getting the one slide that is currently showing.

• FFMPEG is not recording the whole window

  25 mai 2021, par John

  I'm using FFMPEG to record a window as illustrated in the figure below. In all cases, the right hand side of the recorded window is cropped. The command I'm giving is

  



  ffmpeg -f gdigrab -i title="example.txt - Notepad++" output.mkv


  



  Any suggestion on how to fix this problem is much appreciated.

  



  

  



  Here are some additional info :

  



  

  • Running Windows 10

  


  • Using ffmpeg-20181215-011c911-win64-static, but I have the same issue using other versions of FFMPEG

  


  • Desktop resolution is 3200x1800 (dpi scaling issue ?)

  


  



  This is what the recorded area looks like in the example above

  



  

  



  Update 1 :

  



  Recording the whole desktop works fine, however, when recording a region using x and y offsets, the region captured is correct, but the region indicated is wrong. I illustrate this in the image below that shows a screen capture of the desktop during recording. The background image is a grid and the taskbar has been hidden.

  



  

  



  The size of the area to capture is specified to 1280x720, but the region indicated is 1600x900. Also, the x offset is specified to 400px, but the region indicted starts at 500px.

  



  The area recorded is correct ! The image below shows a screenshot of the recording during playback in vlc, note that the "misplaced" region indicator can be seen

  



  

  



  Update 2 :

  



  I noticed that the cursor, the mouse, is not correctly placed when capturing from the desktop, see recording below. Everything looks fine during recording, but at playback the cursor is misplaced.

  



  

  



  The command issued for the recording above was :

  



  ffmpeg -f gdigrab -framerate 30 -offset_x 1820 -offset_y 100 -video_size 1280x720 -i desktop output5.mkv


  



  Windows 10 / ffmpeg-20181215-011c911-win64-static

  


• "Convert regions extracted from wav audio file into Flac audio file " python using FFMPAG in Django

  9 avril 2019, par maryam mehboob

  Regions extracted from wav audio file have "Invalid duration specification for ss"
  For Example in my case duration is in this format

  [(0.006000000000000005, 1.03), (2.0540000000000003, 4.870000000000003)]

  This is for converting regions into Flac format.

       class FLACConverter(object):
  
           # pylint: disable=too-few-public-methods
  
      """
  
           Class for converting a region of an input audio or video file into a FLAC audio file
  
      """
  
  
  
       def __init__(self, source_path, include_before=0.25, include_after=0.25):
  
          self.source_path = source_path
  
          self.include_before = include_before
  
          self.include_after = include_after
  
  
  
  
  
       def __call__(self, region):
  
          try:
  
              print("regions to convert in flac:{}".format(region))
  
              start = region
  
              end = region
  
            #  start = max(0, start - self.include_before)
  
              start = list(map(lambda x: tuple(max(0, y - self.include_before) for y in x), start))
  
              end = list(map(lambda x: tuple(y + self.include_after for y in x), end))
  
              temp = tempfile.NamedTemporaryFile(suffix='.flac', delete=False)
  
              command = ["ffmpeg", "-ss", str(start), "-t", str([tuple(x-y for x, y in zip(x1, x2)) for (x1, x2) in zip(end, start)]),
  
                         "-y", "-i", self.source_path,
  
                         "-loglevel", "error", temp.name]
  
              use_shell = True if os.name == "nt" else False
  
              subprocess.check_output(command)
  
              print(temp.name)
  
              #subprocess.check_output(command, stdin=open(os.devnull), shell=use_shell)
  
              read_data = temp.read()
  
              temp.close()
  
              os.unlink(temp.name)
  
              print("read_data :{}".format(read_data))
  
              print("temp :{}".format(temp.name))
  
  
  
              return read_data
  
  
  
          except KeyboardInterrupt:
  
              return None

  I expect the output of /var/folders/p1/6ttydjfx2sq9zl4cnmjxgjh40000gp/T/tmpwz5n4fnv.flac but it returns an error

  CalledProcessError at /

  Command '['ffmpeg', '-ss', '[(0.006000000000000005, 1.03), (2.0540000000000003, 4.870000000000003)]', '-t', '[(0.5, 0.5), (0.5, 0.5)]', '-y', '-i', '/var/folders/p1/6ttydjfx2sq9zl4cnmjxgjh40000gp/T/tmpuyi5spat.wav', '-loglevel', 'error', '/var/folders/p1/6ttydjfx2sq9zl4cnmjxgjh40000gp/T/tmp0vdewoyd.flac']' returned non-zero exit status 1.```