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• FFmpeg - generate x264 CBR video transport stream with C-API

  6 juillet 2020, par ZeroDefect

  Using various posts sprinkled around the Internet, including this one here on SO, I've been able to understand how to use the FFmpeg cli to generate a CBR video bitrate using the x264 codec (wrapped in an MPEG-2 transport stream). Note : I'm concerned with the video bitrate - nothing else.

  


  ffmpeg -i cbr_test_file_input.mp4 -c:v libx264 -pix_fmt yuv420p -b:v 6000000 -preset fast -tune film -g 25 -x264-params vbv-maxrate=6000:vbv-bufsize=6000:force-cfr=1:nal-hrd=cbr -flags +ildct+ilme x264_cbr_test_output.ts


  


  However, I'm trying to approach this from an FFmpeg C-API point of view. I'm having issues. I've knocked together some code to try do something very similar to what is being done in the FFmpeg CLI. I can generate a transport stream of what I think should be CBR, but the profile of the video bitrate is very different from what I thought was the FFmpeg cli equivalent :

  


  The initialisation of the AVCodecContext looks something like :

  


        av_dict_set(&amp;pDict, "preset", "faster", 0);&#xA;      av_dict_set(&amp;pDict, "tune", "film", 0);&#xA;      av_dict_set_int(&amp;pDict, "rc-lookahead", 25, 0);&#xA;&#xA;      pCdcCtxOut->width = pCdcCtxIn->width;&#xA;      pCdcCtxOut->height = pCdcCtxIn->height;&#xA;      pCdcCtxOut->pix_fmt = AV_PIX_FMT_YUV420P;&#xA;      pCdcCtxOut->gop_size = 25;&#xA;&#xA;      // Going for 6Mbit/s&#xA;      pCdcCtxOut->bit_rate = 6000000;&#xA;      //pCdcCtxOut->rc_min_rate = pCdcCtxOut->bit_rate;&#xA;      pCdcCtxOut->rc_max_rate = pCdcCtxOut->bit_rate;&#xA;      pCdcCtxOut->rc_buffer_size = pCdcCtxOut->bit_rate;&#xA;      pCdcCtxOut->rc_initial_buffer_occupancy = static_cast<int>((pCdcCtxOut->bit_rate * 9) / 10);&#xA;&#xA;      std::string strParams = "vbv-maxrate="&#xA;                              &#x2B; std::to_string(pCdcCtxOut->bit_rate / 1000)&#xA;                              &#x2B; ":vbv-bufsize="&#xA;                              &#x2B; std::to_string(pCdcCtxOut->bit_rate / 1000)&#xA;                              &#x2B; ":force-cfr=1:nal-hrd=cbr";&#xA;&#xA;      av_dict_set(&amp;pDict, "x264-params", strParams.c_str(), 0);&#xA;&#xA;      pCdcCtxOut->field_order = AV_FIELD_TT;&#xA;      pCdcCtxOut->flags = (AV_CODEC_FLAG_INTERLACED_DCT | AV_CODEC_FLAG_INTERLACED_ME | AV_CODEC_FLAG_CLOSED_GOP);&#xA;&#xA;      // WARN: Make some assumptions here!&#xA;      pCdcCtxOut->time_base = AVRational{1,25};&#xA;      pCdcCtxOut->framerate = AVRational{25,1};&#xA;      pCdcCtxOut->sample_aspect_ratio = AVRational{64,45};&#xA;</int>

  


  The output graphs appear very different :

  


  

  


  Above is the FFmpeg CLI output - video bitrate holds fairly steady.

  


  

  


  Above is the output of my sample application - some significant dips in the video bitrate.

  


  I've taken this a step further and created a git repo consisting of :

  


  

  • Code of sample application

  


  • Test input file (.mp4)

  


  • Outputs (.ts file) of tests

  


  • Graphs of output bitrates.

  


  


• FFMpeg- Raw compressed data to video

  21 août 2012, par p.streef

  I'm trying to use FFMpeg to create a video. So far i've been playing with a multiplexing example :
  http://ffmpeg.org/doxygen/trunk/muxing_8c-source.html, and i'm able to create a compressed video from an already existing video.

  Because my program is going to run on an embedded platform I would like to use some custom code (generated by a colleague) to compress the video data and place it into the video file.
  So I'm looking for a way to create a video file in c/c++ using ffmpeg in which i have full control over the compression part (to basically circumvent ffmpeg from doing the compression for me and inserting my own code).

  To clarify i'm planning to use this to save film from an intelligent camera into a compressed h264 mpeg-4 file.

• How to determine webm duration using ffprobe

  23 août 2021, par Lopakhin

  My goal is simple , I have several webm files need to be concated, but first I need to determine their durations.

  



  It seems webm file are played as streams, so there is no way to tell the length of each file.

  



  I have been using ffprobe to do the job ,but the duration returned is N/A.The command I use was :

  



  ffprobe -i input.file -show_format | grep duration


  



  thanks.

  



  The complete output of ffprobe list below :

  



   ffprobe version 2.6.2 Copyright (c) 2007-2015 the FFmpeg developers
  built with Apple LLVM version 6.1.0 (clang-602.0.49) (based on LLVM 3.6.0svn)
  configuration: --prefix=/usr/local/Cellar/ffmpeg/2.6.2 --enable-shared --enable-pthreads --enable-gpl --enable-version3 --enable-hardcoded-tables --enable-avresample --cc=clang --host-cflags= --host-ldflags= --enable-libx264 --enable-libmp3lame --enable-libvo-aacenc --enable-libxvid --enable-libtheora --enable-libvorbis --enable-libvpx --enable-vda
  libavutil      54. 20.100 / 54. 20.100
  libavcodec     56. 26.100 / 56. 26.100
  libavformat    56. 25.101 / 56. 25.101
  libavdevice    56.  4.100 / 56.  4.100
  libavfilter     5. 11.102 /  5. 11.102
  libavresample   2.  1.  0 /  2.  1.  0
  libswscale      3.  1.101 /  3.  1.101
  libswresample   1.  1.100 /  1.  1.100
  libpostproc    53.  3.100 / 53.  3.100
Input #0, matroska,webm, from '231':
  Metadata:
    encoder         : GStreamer matroskamux version 1.5.91
    creation_time   : 2015-12-05 07:59:29
  Duration: N/A, start: 0.000000, bitrate: N/A
    Stream #0:0(eng): Video: vp8, yuv420p, 640x480, SAR 1:1 DAR 4:3, 14.99 fps, 14.99 tbr, 1k tbn, 1k tbc (default)
    Metadata:
      title           : Video
    Stream #0:1(eng): Audio: vorbis, 48000 Hz, stereo, fltp (default)
    Metadata:
      title           : Audio
duration=N/A