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• Video Conferencing in HTML5 : WebRTC via Web Sockets

  14 juin 2012, par silvia

  A bit over a week ago I gave a presentation at Web Directions Code 2012 in Melbourne. Maxine and John asked me to speak about something related to HTML5 video, so I went for the new shiny : WebRTC – real-time communication in the browser.

  Presentation slides

  I only had 20 min, so I had to make it tight. I wanted to show off video conferencing without special plugins in Google Chrome in just a few lines of code, as is the promise of WebRTC. To a large extent, I achieved this. But I made some interesting discoveries along the way. Demos are in the slide deck.

  UPDATE : Opera 12 has been released with WebRTC support.

  Housekeeping : if you want to replicate what I have done, you need to install a Google Chrome Web Browser 19+. Then make sure you go to chrome ://flags and activate the MediaStream and PeerConnection experiment(s). Restart your browser and now you can experiment with this feature. Big warning up-front : it’s not production-ready, since there are still changes happening to the spec and there is no compatible implementation by another browser yet.

  Here is a brief summary of the steps involved to set up video conferencing in your browser :

  1. Set up a video element each for the local and the remote video stream.
  2. Grab the local camera and stream it to the first video element.
  3. (*) Establish a connection to another person running the same Web page.
  4. Send the local camera stream on that peer connection.
  5. Accept the remote camera stream into the second video element.

  Now, the most difficult part of all of this – believe it or not – is the signalling part that is required to build the peer connection (marked with (*)). Initially I wanted to run completely without a server and just enter the remote’s IP address to establish the connection. This is, however, not a functionality that the PeerConnection object provides [might this be something to add to the spec ?].

  So, you need a server known to both parties that can provide for the handshake to set up the connection. All the examples that I have seen, such as https://apprtc.appspot.com/, use a channel management server on Google’s appengine. I wanted it all working with HTML5 technology, so I decided to use a Web Socket server instead.

  I implemented my Web Socket server using node.js (code of websocket server). The video conferencing demo is in the slide deck in an iframe – you can also use the stand-alone html page. Works like a treat.

  While it is still using Google’s STUN server to get through NAT, the messaging for setting up the connection is running completely through the Web Socket server. The messages that get exchanged are plain SDP message packets with a session ID. There are OFFER, ANSWER, and OK packets exchanged for each streaming direction. You can see some of it in the below image :

  

  I’m not running a public WebSocket server, so you won’t be able to see this part of the presentation working. But the local loopback video should work.

  At the conference, it all went without a hitch (while the wireless played along). I believe you have to host the WebSocket server on the same machine as the Web page, otherwise it won’t work for security reasons.

  A whole new world of opportunities lies out there when we get the ability to set up video conferencing on every Web page – scary and exciting at the same time !

• ffmpeg & png watermark issue

  2 décembre 2013, par mindcast

  I tried to create a watermark (using a png image) on a video like this :

  ffmpeg -i test.wmv -b:a 300k -ar 22050 -t 10 -f flv -s 352x288 -vf "movie = watermark_logo352.png [watermark]; [in][watermark] overlay =0:0 [out]" out.flv

  but I get the error :

  ffmpeg version 0.10.4 Copyright (c) 2000-2012 the FFmpeg developers
  
  built on Jun 14 2012 13:14:31 with gcc 4.4.5   configuration:
  
  --prefix=/home/username --enable-cross-compile --enable-shared --arch=amd64 --target-os=linux --disable-yasm --enable-decoder=png --enable-encoder=png   
  
          libavutil      51. 35.100 / 51. 35.100   
  
          libavcodec     53. 61.100 / 53. 61.100   
  
          libavformat    53. 32.100 / 53. 32.100   
  
          libavdevice    53.  4.100 / 53.  4.100   
  
          libavfilter     2. 61.100 /  2. 61.100   
  
          libswscale      2.  1.100 /  2.  1.100   
  
          libswresample   0.  6.100 /  0.  6.100 
  
          Input #0, asf, from 'test.wmv':   
  
          Metadata:
  
              >     WMFSDKVersion   : 9.00.00.2980
  
              >     WMFSDKNeeded    : 0.0.0.0000
  
              >     IsVBR           : 1
  
              >     VBR Peak        : 351
  
              >     Buffer Average  : 728   Duration: 00:00:05.59, start: 0.000000, bitrate: 574 kb/s
  
              >     Stream #0:0(jpn): Audio: wmav2 (a[1][0][0] / 0x0161), 22050 Hz, 2 channels, s16, 32 kb/s
  
              >     Stream #0:1(jpn): Video: wmv1 (WMV1 / 0x31564D57), yuv420p, 352x288, 520 kb/s, SAR 8:9 DAR 88:81, 29.97 tbr, 1k tbn, 1k tbc File
  
              > 'out2.flv' already exists. Overwrite ? [y/N] y w:352 h:288
  
              > pixfmt:yuv420p tb:1/1000000 sar:8/9 sws_param: 
  
      [image2 @ 0x551f880] decoding for stream 0 failed 
  
      [image2 @ 0x551f880] Could not find codec parameters (Video: png) 
  
      [movie @ 0x551f440] Failed to find stream info
  
      [movie @ 0x551f440] Failed to find any codec 
  
      Error initializing filter 'movie' with args 'watermark_logo352.png' 
  
      Error opening filters!

  When I use a jpg, it works like a charm.

  I'm use ffmpeg v 0.10.4 on Debian 6 Squeeze.
  Any help would be much appreciated.

  EDIT

  The problem is simpler than i thought. If i use ffmpeg -i with any png image i get a similar error :

    libavutil      51. 35.100 / 51. 35.100
  
    libavcodec     53. 61.100 / 53. 61.100
  
    libavformat    53. 32.100 / 53. 32.100
  
    libavdevice    53.  4.100 / 53.  4.100
  
    libavfilter     2. 61.100 /  2. 61.100
  
    libswscale      2.  1.100 /  2.  1.100
  
    libswresample   0.  6.100 /  0.  6.100
  
    libpostproc    52.  0.100 / 52.  0.100
  
  [image2 @ 0xc8b73a0] decoding for stream 0 failed
  
  [image2 @ 0xc8b73a0] Could not find codec parameters (Video: png)
  
  watermark.png: could not find codec parameters

• ffmpeg not giving correct duration of a mp4

  1er juin 2012, par oach

  I am working with ffmpeg to convert videos into flv files via php. The tests I have done do not work for mp4 conversions. I have a 13 second video (videos will be limited to 15 seconds), when it is uploaded and I check the "duration" of the video it comes out over 300 seconds. I have tried changing around how I process the video :

  // original
  
  exec(&#39;ffmpeg -i <path>/<filename> 2>&amp;1&#39;, $output);
  
  
  
  // current
  
  exec(&#39;ffmpeg -i <path>/<filename> 2>&amp;1 | grep "Duration" | cut -d \&#39; \&#39; -f 4 | sed s/,//&#39;, $output);
  
  </filename></path></filename></path>

  The original method did not work for mpg files but the second does, but neither gives me the "correct" duration of a mp4 video. Is there a "special" way to process mp4 files ?

  Thank you for your time and help.

  Update :

  Command line

  ffmpeg -i ./custom_scraping.mp4 2>&1 | grep "Duration" | cut -d ' ' -f 4 | sed s/,//
  
  00:05:15.84

  Complete output (formatted as best I could)

  ffmpeg -i ./custom_scraping.mp4 2>&1
  
  FFmpeg version 0.6.5, Copyright (c) 2000-2010 the FFmpeg developers
  
  built on Jan 29 2012 23:55:02 with gcc 4.1.2 20080704 (Red Hat 4.1.2-51)
  
  configuration: --prefix=/usr --libdir=/usr/lib64 --shlibdir=/usr/lib64 --mandir=/usr/share/man --incdir=/usr/include --disable-avisynth --extra-cflags='-O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m64 -mtune=generic -fPIC' --enable-avfilter --enable-avfilter-lavf --enable-libdirac --enable-libfaac --enable-libfaad --enable-libfaadbin --enable-libgsm --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libx264 --enable-gpl --enable-nonfree --enable-postproc --enable-pthreads --enable-shared --enable-swscale --enable-vdpau --enable-version3 --enable-x11grab
  
  libavutil     50.15. 1 / 50.15. 1
  
  libavcodec    52.72. 2 / 52.72. 2
  
  libavformat   52.64. 2 / 52.64. 2
  
  libavdevice   52. 2. 0 / 52. 2. 0
  
  libavfilter    1.19. 0 /  1.19. 0
  
  libswscale     0.11. 0 /  0.11. 0
  
  libpostproc   51. 2. 0 / 51. 2. 0
  
  
  
  Seems stream 1 codec frame rate differs from container frame rate: 5994.00 (5994/1) -> 29.97 (2997/100)
  
  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from './custom_scraping.mp4':
  
  Metadata:
  
  major_brand     : mp42
  
  minor_version   : 1
  
  compatible_brands: mp42avc1
  
  Duration: 00:05:15.84, start: 0.000000, bitrate: 36 kb/s
  
  Stream #0.0(eng): Audio: aac, 44100 Hz, stereo, s16, 2 kb/s
  
  Stream #0.1(eng): Video: h264, yuv420p, 480x360, 36 kb/s, 1.04 fps, 29.97 tbr, 2997 tbn, 5994 tbc

  At least one output file must be specified

  Don't know if it helps but from the listing of the file in Linux :
  1432471 May 31 13:33 custom_scraping.mp4

  Let me know if anything else is needed.