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• Streaming live video with avconv/ffmped on nginx rtmp server player error

  6 juin 2014, par user3715403

  Good morning,
  My current project involves playing live video (testing using a usb webcam for now). I compiled and installed nginx server with the rtmp module (obtained from https://github.com/arut/nginx-rtmp-module). The nginx configuration file is as :

  worker_processes  1;
  
  
  
  error_log  logs/error.log debug;
  
  
  
  events {
  
      worker_connections  1024;
  
  }
  
  
  
  rtmp {
  
      server {
  
          listen 1935;
  
  
  
          application myapp {
  
              live on;
  
  
  
              #record keyframes;
  
              #record_path /tmp;
  
              #record_max_size 128K;
  
              #record_interval 30s;
  
              #record_suffix .this.is.flv;
  
  
  
              #on_publish http://localhost:8080/publish;
  
              #on_play http://localhost:8080/play;
  
              #on_record_done http://localhost:8080/record_done;
  
          }
  
      }
  
  }
  
  
  
  http {
  
      server {
  
          listen      8080;
  
  
  
          location /stat {
  
              rtmp_stat all;
  
              rtmp_stat_stylesheet stat.xsl;
  
          }
  
  
  
          location /stat.xsl {
  
              root /path/to/nginx-rtmp-module/;
  
          }
  
  
  
          location /control {
  
              rtmp_control all;
  
          }
  
  
  
          #location /publish {
  
          #    return 201;
  
          #}
  
  
  
          #location /play {
  
          #    return 202;
  
          #}
  
  
  
          #location /record_done {
  
          #    return 203;
  
          #}
  
  
  
          location /rtmp-publisher {
  
              root /path/to/nginx-rtmp-module/test;
  
          }
  
  
  
          location / {
  
              root /path/to/nginx-rtmp-module/test/www;
  
          }
  
      }
  
  }

  The command line to start streaming is as :

  avconv -s vga -f video4linux2 -i /dev/video0 -vcodec libx264 -an -f flv -b 800k -r 30 rtmp://localhost/myapp/live

  While streaming, the following stats are displayed :

  avconv version 10.1, Copyright (c) 2000-2014 the Libav developers
  
    built on May 13 2014 15:13:23 with gcc 4.6 (Ubuntu/Linaro 4.6.3-1ubuntu5)
  
  [video4linux2 @ 0x2f06220] Estimating duration from bitrate, this may be inaccurate
  
  Input #0, video4linux2, from '/dev/video0':
  
    Duration: N/A, start: 112393.305806, bitrate: 73728 kb/s
  
      Stream #0.0: Video: rawvideo, yuyv422, 640x480, 73728 kb/s, 15 fps, 1000k tbn
  
  [libx264 @ 0x2f187a0] using cpu capabilities: MMX2 SSE2Fast SSSE3 FastShuffle SSE4.2 AVX
  
  [libx264 @ 0x2f187a0] profile High, level 3.0
  
  [libx264 @ 0x2f187a0] 264 - core 120 r2151 a3f4407 - H.264/MPEG-4 AVC codec - Copyleft 2003-2011 - http://www.videolan.org/x264.html - options: cabac=1 ref=3 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=7 psy=1 psy_rd=1.00:0.00 mixed_ref=1 me_range=16 chroma_me=1 trellis=1 8x8dct=1 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=-2 threads=1 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=3 b_pyramid=2 b_adapt=1 b_bias=0 direct=1 weightb=1 open_gop=0 weightp=2 keyint=250 keyint_min=25 scenecut=40 intra_refresh=0 rc_lookahead=40 rc=abr mbtree=1 bitrate=800 ratetol=1.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
  
  Output #0, flv, to 'rtmp://localhost/myapp/live':
  
    Metadata:
  
      encoder         : Lavf55.12.0
  
      Stream #0.0: Video: libx264, yuv420p, 640x480, q=-1--1, 800 kb/s, 1k tbn, 30 tbc
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (rawvideo -> libx264)
  
  Press ctrl-c to stop encoding
  
  frame= 3283 fps= 30 q=26.0 size=   10592kB time=108.33 bitrate= 810.5kbits/s

  Before embedding the stream onto a web page using, say videojs, I am using avplay which returns the error : rtmp ://localhost/myapp/live : Input/output error while VLC returns the error
  Your input can’t be opened :
  VLC is unable to open the MRL ’rtmp ://localhost/myapp/live’. Check the log for details.

  Any suggestions about what would cause the errors displayed by VLC/avplay ?

  Thanks
  Daniel

• What is “interoperable TTML” ?

  19 septembre 2012, par silvia

  I’ve just tried to come to terms with the latest state of TTML, the Timed Text Markup Language.

  TTML has been specified by the W3C Timed Text Working Group and released as a RECommendation v1.0 in November 2010. Since then, several organisations have tried to adopt it as their caption file format. This includes the SMPTE, the EBU (European Broadcasting Union), and Microsoft.

  Both, Microsoft and the EBU actually looked at TTML in detail and decided that in order to make it usable for their use cases, a restriction of its functionalities is needed.

  EBU-TT

  The EBU released EBU-TT, which restricts the set of valid attributes and feature. “The EBU-TT format is intended to constrain the features provided by TTML, especially to make EBU-TT more suitable for the use with broadcast video and web video applications.” (see EBU-TT).

  In addition, EBU-specific namespaces were introduce to extend TTML with EBU-specific data types, e.g. ebuttdt:frameRateMultiplierType or ebuttdt:smpteTimingType. Similarly, a bunch of metadata elements were introduced, e.g. ebuttm:documentMetadata, ebuttm:documentEbuttVersion, or ebuttm:documentIdentifier.

  The use of namespaces as an extensibility mechanism will ascertain that EBU-TT files continue to be valid TTML files. However, any vanilla TTML parser will not know what to do with these custom extensions and will drop them on the floor.

  Simple Delivery Profile

  With the intention to make TTML ready for “internet delivery of Captions originated in the United States”, Microsoft proposed a “Simple Delivery Profile for Closed Captions (US)” (see Simple Profile). The Simple Profile is also a restriction of TTML.

  Unfortunately, the Microsoft profile is not the same as the EBU-TT profile : for example, it contains the “set” element, which is not conformant in EBU-TT. Similarly, the supported style features are different, e.g. Simple Profile supports “display-region”, while EBU-TT does not. On the other hand, EBU-TT supports monospace, sans-serif and serif fonts, while the Simple profile does not.

  Thus files created for the Simple Delivery Profile will not work on players that expect EBU-TT and the reverse.

  Fortunately, the Simple Delivery Profile does not introduce any new namespaces and new features, so at least it is an explicit subpart of TTML and not both a restriction and extension like EBU-TT.

  SMPTE-TT

  SMPTE also created a version of the TTML standard called SMPTE-TT. SMPTE did not decide on a subset of TTML for their purposes – it was simply adopted as a complete set. “This Standard provides a framework for timed text to be supported for content delivered via broadband means,…” (see SMPTE-TT).

  However, SMPTE extended TTML in SMPTE-TT with an ability to store a binary blob with captions in another format. This allows using SMPTE-TT as a transport format for any caption format and is deemed to help with “backwards compatibility”.

  Now, instead of specifying a profile, SMPTE decided to define how to convert CEA-608 captions to SMPTE-TT. Even if it’s not called a “profile”, that’s actually what it is. It even has its own namespace : “m608 :”.

  Conclusion

  With all these different versions of TTML, I ask myself what a video player that claims support for TTML will do to get something working. The only chance it has is to implement all the extensions defined in all the different profiles. I pity the player that has to deal with a SMPTE-TT file that has a binary blob in it and is expected to be able to decode this.

  Now, what is a caption author supposed to do when creating TTML ? They obviously cannot expect all players to be able to play back all TTML versions. Should they create different files depending on what platform they are targeting, i.e. a EBU-TT version, a SMPTE-TT version, a vanilla TTML version, and a Simple Delivery Profile version ? Should they by throwing all the features of all the versions into one TTML file and hope that the players will pick out the right things that they require and drop the rest on the floor ?

  Maybe the best way to progress would be to make a list of the “safe” features : those features that every TTML profile supports. That may be the best way to get an “interoperable TTML” file. Here’s me hoping that this minimal set of features doesn’t just end up being the usual (starttime, endtime, text) triple.

  UPDATE :

  I just found out that UltraViolet have their own profile of SMPTE-TT called CFF-TT (see UltraViolet FAQ and spec). They are making some SMPTE-TT fields optional, but introduce a new @forcedDisplayMode attribute under their own namespace “cff :”.

• Unknown reason of an error while debugging an Opencv project using opencv2 functions

  30 mars 2013, par Animesh Pandey

  I have openCV 2.3 and I am using Visual Studio 2010.

      ...
  
  VideoCapture cap;
  
  cap.open("Video.avi");
  
  if( !cap.isOpened() )
  
  {
  
  
  
      puts("***Could not initialize capturing...***\n");
  
      system("Pause");
  
      return 0;
  
  } ...

  This is a code snippet of the while program.
  I added a system command in order to hold the output window. I got no errors while building the project but when I began debugging, the output window had this output :

  warning: Error opening file (../../modules/highgui/src/cap_ffmpeg_impl.hpp:477)
  
  ***Could not initialize capturing...***
  
  
  
  Press any key to continue . . .

  I checked this directory, the file is available but then why is it that it doesn't open ?
  I even have the opencv_ffmpeg.dll in the bin folder with its path added to System Paths.
  Still I get this same error ....
  I even checked first 3 pages of google search I did but could not find an answer.
  So please help !

  ---

  The error which I mentioned is because, there has been an error in opening the .avi file ...
  This is the part of code in cap_ffmpeg_impl.hpp -

  int err = av_open_input_file(&ic, _filename, NULL, 0, NULL);
  
  if (err < 0) {
  
      CV_WARN("Error opening file"); //Error part
  
      goto exit_func;
  
  }

  This file is available at D :\OpenCV2.3\opencv\modules\highgui\src. When I make any changes in this file, they do not reflect on the output window and when I removed this file, even then it did not give any error !:O
  I am not able to understand what is happening ....??