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• WebRTC books – a brief review

  1er janvier 2014, par silvia

  I just finished reading Rob Manson’s awesome book “Getting Started with WebRTC” and I can highly recommend it for any Web developer who is interested in WebRTC.

  Rob explains very clearly how to create your first video, audio or data peer-connection using WebRTC in current Google Chrome or Firefox (I think it also now applies to Opera, though that wasn’t the case when his book was published). He makes available example code, so you can replicate it in your own Web application easily, including the setup of a signalling server. He also points out that you need a ICE (STUN/TURN) server to punch through firewalls and gives recommendations for what software is available, but stops short of explaining how to set them up.

  Rob’s focus is very much on the features required in a typical Web application :

  • video calls
  • audio calls
  • text chats
  • file sharing

  In fact, he provides the most in-depth demo of how to set up a good file sharing interface I have come across.

  Rob then also extends his introduction to WebRTC to two key application areas : education and team communication. His recommendations are spot on and required reading for anyone developing applications in these spaces.

  —

  Before Rob’s book, I have also read Alan Johnson and Dan Burnett’s “WebRTC” book on APIs and RTCWEB protocols of the HTML5 Real-Time Web.

  Alan and Dan’s book was written more than a year ago and explains that state of standardisation at that time. It’s probably a little out-dated now, but it still gives you good foundations on why some decisions were made the way they are and what are contentious issues (some of which still remain). If you really want to understand what happens behind the scenes when you call certain functions in the WebRTC APIs of browsers, then this is for you.

  Alan and Dan’s book explains in more details than Rob’s book how IP addresses of communication partners are found, how firewall holepunching works, how sessions get negotiated, and how the standards process works. It’s probably less useful to a Web developer who just wants to implement video call functionality into their Web application, though if something goes wrong you may find yourself digging into the details of SDP, SRTP, DTLS, and other cryptic abbreviations of protocols that all need to work together to get a WebRTC call working.

  —

  Overall, both books are worthwhile and cover different aspects of WebRTC that you will stumble across if you are directly dealing with WebRTC code.

• Can you put the result of a blackdetect filter in a textfile using ffmpeg ?

  9 mars 2017, par Gijserman

  I’m testing out the "blackdetect" filter in ffmpeg. I want to have the times when the video is black to be read by a script (like actionscript or javascript). I tried :

  ffmpeg -i video1.mp4 -vf "blackdetect=d=2:pix_th=0.00" -an -f null -

  And I get a nice result in the ffmpeg log :

  ffmpeg version N-55644-g68b63a3 Copyright (c) 2000-2013 the FFmpeg developers
  
    built on Aug 19 2013 20:32:00 with gcc 4.7.3 (GCC)
  
    configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-av
  
  isynth --enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnutls --enab
  
  le-iconv --enable-libass --enable-libbluray --enable-libcaca --enable-libfreetyp
  
  e --enable-libgsm --enable-libilbc --enable-libmodplug --enable-libmp3lame --ena
  
  ble-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-l
  
  ibopus --enable-librtmp --enable-libschroedinger --enable-libsoxr --enable-libsp
  
  eex --enable-libtheora --enable-libtwolame --enable-libvo-aacenc --enable-libvo-
  
  amrwbenc --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libxavs --
  
  enable-libxvid --enable-zlib
  
    libavutil      52. 42.100 / 52. 42.100
  
    libavcodec     55. 28.100 / 55. 28.100
  
    libavformat    55. 13.103 / 55. 13.103
  
    libavdevice    55.  3.100 / 55.  3.100
  
    libavfilter     3. 82.100 /  3. 82.100
  
    libswscale      2.  5.100 /  2.  5.100
  
    libswresample   0. 17.103 /  0. 17.103
  
    libpostproc    52.  3.100 / 52.  3.100
  
  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'video1.mp4':
  
    Metadata:
  
      major_brand     : isom
  
      minor_version   : 512
  
      compatible_brands: isomiso2avc1mp41
  
      creation_time   : 1970-01-01 00:00:00
  
      encoder         : Lavf53.13.0
  
    Duration: 00:02:01.54, start: 0.000000, bitrate: 275 kb/s
  
      Stream #0:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 768x432 [
  
  SAR 1:1 DAR 16:9], 211 kb/s, 25 fps, 25 tbr, 25 tbn, 50 tbc
  
      Metadata:
  
        creation_time   : 1970-01-01 00:00:00
  
        handler_name    : VideoHandler
  
      Stream #0:1(eng): Audio: aac (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 59
  
   kb/s
  
      Metadata:
  
        creation_time   : 1970-01-01 00:00:00
  
        handler_name    : SoundHandler
  
  Output #0, null, to 'pipe:':
  
    Metadata:
  
      major_brand     : isom
  
      minor_version   : 512
  
      compatible_brands: isomiso2avc1mp41
  
      encoder         : Lavf55.13.103
  
      Stream #0:0(eng): Video: rawvideo (I420 / 0x30323449), yuv420p, 768x432 [SAR
  
   1:1 DAR 16:9], q=2-31, 200 kb/s, 90k tbn, 25 tbc
  
      Metadata:
  
        creation_time   : 1970-01-01 00:00:00
  
        handler_name    : VideoHandler
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (h264 -> rawvideo)
  
  Press [q] to stop, [?] for help
  
  [null @ 00000000003279a0] Encoder did not produce proper pts, making some up.
  
  [blackdetect @ 0000000004d5e800] black_start:0 black_end:17.08 black_duration:17
  
  .08
  
  [blackdetect @ 0000000004d5e800] black_start:62.32 black_end:121.48 black_durati
  
  on:59.16
  
  frame= 3038 fps=2317 q=0.0 Lsize=N/A time=00:02:01.52 bitrate=N/A
  
  video:285kB audio:0kB subtitle:0 global headers:0kB muxing overhead -100.007543%

  And I’m particularly interested in this part :

  [blackdetect @ 0000000004e2e340] black_start:0 black_end:17.08 black_duration:17.08
  
  [blackdetect @ 0000000004e2e340] black_start:62.32 black_end:121.48 black_duration:59.16

  So my question :

  1. Is there a way to only take the blackdetect filter output and put it in a .txt file ?
  2. And if this is possible, is there a way to do this in a statement with multiple video inputs ? Like in this example

  ---

  example :

  ffmpeg -f concat -i mylist.txt -c copy concat.mp4

  Where mylist.txt is a list of videos :

  file 'video1.mp4'
  
  file 'video2.mp4'
  
  file 'video3.mp4'
  
  file 'video4.mp4'

  ---

  Basically what I want to have is one or more text files containing information about the black frames in every video in this list to be used by another program

• reading lines from txt file into .csv

  7 janvier 2014, par Dynamite Media

  i have a .TXT file i created via batch file using ffmpeg. it returns the following info ( more but trying to make short)

  major_brand=isom 
  
  minor_version=512 
  
  compatible_brands=isomiso2avc1mp41 
  
  creation_time=1970-01-01 00:00:00 
  
  encoder=Lavf53.19.0 
  
  genre=sport 
  
  track=1 
  
  title=IRWX_TV_Vol_01_1_Pt_4 
  
  episode_id=0101 

  the .TXT file comes back with 3 of these above. well i want to be able to only use some of the info above and then i want to create a .CSV file so that i can load into .XLS file

  I have used the following and it's close :

  REM now lets get info we need from result.txt
  
  pause 
  
  
  
  REM checks how many times finds genre and loops that many times
  
  FOR /f "delims=" %%b IN ('findstr "genre" result.txt') DO (
  
  for %%f in (result.txt) do (
  
      set i=0
  
  
  
  for /F "delims= tokens=2,3*" %%l in (%%f) do (
  
      set /A i+=1
  
      set line!i!=%%l
  
  
  
  )
  
  echo  !line9!, !line6!, !line8!,  >> result.csv
  
  )
  
  ) 
  
  pause 

  and this is coming back with the following :

   title=IRWX_TV_Vol_01_1_Pt_4 , genre=sport, episode_id=0101
  
   title=IRWX_TV_Vol_01_1_Pt_4 , genre=sport, episode_id=0101
  
   title=IRWX_TV_Vol_01_1_Pt_4 , genre=sport, episode_id=0101

  ONLY the 1st video title from .TXT file and not each of them

  AND i would prefer it to come back like this :

   IRWX_TV_Vol_01_1_Pt_4,sport,0101

  Minus the variables, the "=" and the space issues you see above.

  i have been going over and over this trying different things and it is just not working.

  Hopefully someone here can see the issue and help out, Thanks