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• How to send MPEGTS streams over UDP

  24 décembre 2015, par pAkY88

  I am developing a realtime video-streaming system which is composed basically by a server and several clients.

  For now, let’s ignore how packets are forwarded among the server and the clients, let’s focus just on how the server can send a MPEGTS stream over UDP packets.

  The stream is encoded in MPEGTS format.

  What I’m trying to do is reading some packets (the main question is "how many ?") and encapsulating them in UDP packets. The destination (a client) reads these UDP packets and then forward them to VLC, which is able to play MPEGTS network streams by reading UDP packets.

  If I send only video packets, everything works fine, instead if I try to encapsulate in the same UDP packet, both some video packets and some audio packets, VLC is not able to decode and play the stream.
  I read somewhere that each UDP packet should contain 7 TS packets, but unfortunately even if I comply with this rule, VLC doesn’t decode the stream correctly.

  Here is a sample code of my program : http://pastebin.com/evMi6FkY

  How should I encapsulate MPEGTS packets in UDP packets ?

  Thanks !

• c++, FFMPEG, H264, creating zero-delay stream

  5 février 2015, par Mat

  I’m trying to encode video (using h264 codec at the moment, but other codecs would be fine too if better suited for my needs) such that the data needed for decoding is available directly after a frame (including the first frame) was encoded (so, i want only I and P frames, no B frames).

  How do I need to setup the AVCodecContext to get such a stream ? So far my testing arround with the values still always resulted in avcodec_encode_video() returning 0 on the first frame.

  //edit : this is currently my setup code of the AVCodecContext :

  static AVStream* add_video_stream(AVFormatContext *oc, enum CodecID codec_id, int w, int h, int fps)
  
  {
  
      AVCodecContext *c;
  
      AVStream *st;
  
      AVCodec *codec;
  
  
  
      /* find the video encoder */
  
      codec = avcodec_find_encoder(codec_id);
  
      if (!codec) {
  
          fprintf(stderr, "codec not found\n");
  
          exit(1);
  
      }
  
  
  
      st = avformat_new_stream(oc, codec);
  
      if (!st) {
  
          fprintf(stderr, "Could not alloc stream\n");
  
          exit(1);
  
      }
  
  
  
      c = st->codec;
  
  
  
      /* Put sample parameters. */
  
      c->bit_rate = 400000;
  
      /* Resolution must be a multiple of two. */
  
      c->width    = w;
  
      c->height   = h;
  
      /* timebase: This is the fundamental unit of time (in seconds) in terms
  
       * of which frame timestamps are represented. For fixed-fps content,
  
       * timebase should be 1/framerate and timestamp increments should be
  
       * identical to 1. */
  
      c->time_base.den = fps;
  
      c->time_base.num = 1;
  
      c->gop_size      = 12; /* emit one intra frame every twelve frames at most */
  
  
  
      c->codec = codec;
  
      c->codec_type = AVMEDIA_TYPE_VIDEO;
  
      c->coder_type = FF_CODER_TYPE_VLC;
  
      c->me_method = 7; //motion estimation algorithm
  
      c->me_subpel_quality = 4;
  
      c->delay = 0; 
  
      c->max_b_frames = 0; 
  
      c->thread_count = 1; // more than one threads seem to increase delay
  
      c->refs = 3;
  
  
  
      c->pix_fmt       = PIX_FMT_YUV420P;
  
  
  
      /* Some formats want stream headers to be separate. */
  
      if (oc->oformat->flags & AVFMT_GLOBALHEADER)
  
          c->flags |= CODEC_FLAG_GLOBAL_HEADER;
  
  
  
      return st;
  
  }

  but with this avcodec_encode_video() will buffer 13 frames before returning any bytes (after that, it will return bytes on every frame). if I set gop_size to 0, then avcodec_encode_video() will return bytes only after the second frame was passed to it. I need a zero delay though.

  This guy apparently was successful (even with larger gop) : http://mailman.videolan.org/pipermail/x264-devel/2009-May/005880.html but I don’t see what he is doing differently

• Revision 37642 : On échappe les balises fermantes dans le js pour la compat xhtml On ...

  24 avril 2010, par kent1@… — Log

  On échappe les balises fermantes dans le js pour la compat xhtml
  On définit ’ajax_image_searching’ s’il ne l’est pas (dans l’espace public)
  On place mieux la roue ajax dans le tr (Dans le dernier td en fait)
  On repositionne le focus sur l’élément cliqué
  Du coup on peut supprimer des lignes de css qui ne servent plus trop