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• Extremely high bit rate when encoding video with libavcodec

  10 janvier 2014, par niculare

  I am trying to capture the camera output and make a video using libavcodec. As an example on how to accomplish this i have used ffmpeg muxing example.

  The problem is that a 4 seconds video has a size of 15mb and a bitrate of 30000 kb/s, although I have set the bitrate on AVCodecContext to 400000 (I consider this value is in bits / sec, not kb/s).

  I have also tried to record the video using ffmpeg from command line and it has a bitrate of 700 kb/s.

  Does anybody have an idea why the bitrate is not preserved and thus the resulting file is very large ? The code I have used to initialize the codec context is below :

  initialization part :

  avformat_alloc_output_context2(&m_formatContext, NULL, NULL, filename);
  
  outputFormat = m_formatContext->oformat;
  
  
  
  codec = avcodec_find_encoder(outputFormat->video_codec);
  
  
  
  m_videoStream = avformat_new_stream(m_formatContext, codec);
  
  
  
  m_videoStream->id = m_formatContext->nb_streams - 1;
  
  
  
  codecContext = m_videoStream->codec;
  
  
  
  codecContext->codec_id = outputFormat->video_codec;
  
  
  
  codecContext->width = m_videoResolution.width();
  
  codecContext->height = m_videoResolution.height();
  
  
  
  int m_bitRate = 400000;
  
  codecContext->bit_rate = m_bitRate;
  
  codecContext->rc_min_rate = m_bitRate;
  
  codecContext->rc_max_rate = m_bitRate;
  
  codecContext->bit_rate_tolerance = 0;
  
  
  
  codecContext->time_base.den = 20;
  
  codecContext->time_base.num = 1;
  
  
  
  codecContext->pix_fmt = AV_PIX_FMT_YUV422P;
  
  
  
  if (m_formatContext->oformat->flags & AVFMT_GLOBALHEADER)
  
      codecContext->flags |= CODEC_FLAG_GLOBAL_HEADER;
  
  /* open it */
  
  ret = avcodec_open2(codecContext, codec, NULL);
  
  
  
  avFrame = avcodec_alloc_frame();
  
  
  
  ret = avpicture_alloc(&avPicture, codecContext->pix_fmt, codecContext->width, codecContext->height);
  
  
  
  *((AVPicture *)avFrame) = avPicture;
  
  
  
  av_dump_format(m_formatContext, 0, filename, 1);
  
  
  
  if (!(outputFormat->flags & AVFMT_NOFILE)) {
  
      ret = avio_open(&m_formatContext->pb, filename, AVIO_FLAG_WRITE);
  
  }
  
  
  
  ret = avformat_write_header(m_formatContext, NULL);
  
  
  
  if (avFrame)
  
      avFrame->pts = 0;

• Files created with a direct stream copy using FFmpeg's libavformat API play back too fast at 3600 fps

  2 octobre 2013, par Chris Ballinger

  I am working on a libavformat API wrapper that converts MP4 files with H.264 and AAC to MPEG-TS segments suitable for streaming. I am just doing a simple stream copy without re-encoding, but the files I produce play the video back at 3600 fps instead of 24 fps.

  Here are some outputs from ffprobe https://gist.github.com/chrisballinger/6733678, the broken file is below :

  r_frame_rate=1/1
  
  avg_frame_rate=0/0
  
  time_base=1/90000
  
  start_pts=0
  
  start_time=0.000000
  
  duration_ts=2999
  
  duration=0.033322

  The same input file manually sent through ffmpeg has proper timestamp information :

  r_frame_rate=24/1
  
  avg_frame_rate=0/0
  
  time_base=1/90000
  
  start_pts=126000
  
  start_time=1.400000
  
  duration_ts=449850
  
  duration=4.998333

  I believe the problem lies somewhere in my setup of libavformat here : https://github.com/OpenWatch/FFmpegWrapper/blob/master/FFmpegWrapper/FFmpegWrapper.m#L349 where I repurposed a bunch of code from ffmpeg.c that was required for the direct stream copy.

  Since 3600 seems like a "magic number" (60*60), it could be as simple as me not setting the time scale properly, but I can't figure out where my code diverges from ffmpeg/avconv itself.

  Similar question here, but I don't think they got as far as I did : Muxing a H.264 Annex B & AAC stream using libavformat with vcopy/acopy

• How to concat two/many mp4 files(Mac OS X Lion 10.7.5) with different resolution, bit rate [on hold]

  3 septembre 2013, par praveen

  I have to concat different mp4 files into single mp4 file. i am using following ffmpeg command but this command is only working if both file is same(copy, or if all video property is same(codec, resolution,bitrate....) ) other wise result is unexpected video. (I am working on Mac OS X Lion 10.7.5)

  ffmpeg commad :

  ffmpeg -i images/1/output.mp4 -c copy -bsf:v h264_mp4toannexb -f mpegts intermediate1.ts
  
  ffmpeg -i images/1/Video2.mp4 -c copy -bsf:v h264_mp4toannexb -f mpegts intermediate2.ts
  
  ffmpeg -i "concat:intermediate1.ts|intermediate2.ts" -c copy -bsf:a aac_adtstoasc output2.mp4

  console output :

  [mpegts @ 0x7f8c6c03d800] max_analyze_duration 5000000 reached at 5000000 microseconds
  
  
  
  Input #0, mpegts, from 'concat:intermediate1.ts|intermediate2.ts':
  
  Duration: 00:00:16.52, start: 1.400000, bitrate: 1342 kb/s
  
  Program 1 
  
  Metadata:
  
  service_name    : Service01
  
  service_provider: FFmpeg
  
  Stream #0:0[0x100]: Video: h264 (Main) ([27][0][0][0] / 0x001B), yuv420p, 1024x768 [SAR   1:1 DAR 4:3], 25 fps, 25 tbr, 90k tbn, 50 tbc
  
  Stream #0:1[0x101](und): Audio: aac ([15][0][0][0] / 0x000F), 48000 Hz, stereo, fltp, 101 kb/s
  
  
  
  
  
  
  
  Output #0, mp4, to 'output2.mp4':
  
  Metadata:
  
  encoder         : Lavf54.63.104
  
  Stream #0:0: Video: h264 ([33][0][0][0] / 0x0021), yuv420p, 1024x768 [SAR 1:1 DAR 4:3],      q=2-31, 25 fps, 90k tbn, 90k tbc
  
  Stream #0:1(und): Audio: aac ([64][0][0][0] / 0x0040), 48000 Hz, stereo, 101 kb/s
  
   Stream mapping:
  
  Stream #0:0 -> #0:0 (copy)
  
  Stream #0:1 -> #0:1 (copy)
  
  Press [q] to stop, [?] for help
  
   frame=  586 fps=0.0 q=-1.0 Lsize=    2449kB time=00:00:20.11 bitrate= 997.4kbits/s    
  
   video:2210kB audio:225kB subtitle:0 global headers:0kB muxing overhead 0.578335%

  Please help