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• 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

• FFMPEG and libavfilter

  21 mars 2012, par Sergio

  With the currently installed ffmpeg I can't post watermark on converted videos. Can the reason for that be that I have not installed libavfilter library ?

  Currently # ffmpeg -v looks like :

  FFmpeg version SVN-r20374, Copyright (c) 2000-2009 Fabrice Bellard, et al.
  
  built on Oct 26 2009 22:47:01 with gcc 4.1.2 20080704 (Red Hat 4.1.2-46)
  
  configuration: --enable-libmp3lame --enable-libopencore-amrnb --enable-version3 -   enable-libopencore-amrwb --enable-version3 --enable-nonfree --enable-libfaad --enable-gpl - -disable-mmx --enable-shared --enable-libfaac --enable-libvorbis
  
  libavutil     50. 3. 0 / 50. 3. 0
  
  libavcodec    52.37. 1 / 52.37. 1
  
  libavformat   52.39. 2 / 52.39. 2
  
  libavdevice   52. 2. 0 / 52. 2. 0

  As you can see I'm missing libavfilter ? How can I add that library to FFMPEG and successfully add watermark on videos ?

  Thanks for any help.

• ffmpeg, replace part of audio in mp4 video file

  20 décembre 2018, par user2903753

  I want to replace part of the audio in one mp4 file with part of another mp3 file using ffmpeg.
  this is what I’m trying to do :

  ffmpeg -i 2009.mp4 -i birds.mp3 -filter_complex "[0:a]atrim=end=45,asetpts=PTS-STARTPTS[aud1];[1:a]atrim=0:18,asetpts=PTS-STARTPTS[aud2];  [0:a]atrim=start=63,asetpts=PTS-STARTPTS[aud3]; [aud1][aud2][aud3]concat=n=3:v=0:a=1[aout]"  -map 0:v -map "[aout]" -c:v copy   output.mp4

  it is giving me this error :

  [NULL @ 000000000596e020] Unable to find a suitable output format for
  ’ffmpeg’ ffmpeg : Invalid argument