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• FFmpeg converting two videos with dynamic frame rates - dup/drop frames

  18 décembre 2017, par Matho

  I have problems with converting two videos using ffmpeg. Those videos have dynamic frame rate. I’m using this ffmpeg command :

  ffmpeg -y -i /storage/emulated/0/Movies/RMR/RMR_camera_2017-10-04-20-42-56.mp4 -i /storage/emulated/0/Movies/RMR/RMR_screen_2017-10-04-20-42-56.mp4 -strict experimental -preset ultrafast -filter_complex [0]scale=iw/4:ih/4[pip];[pip]transpose=2[rotate];[1][rotate]overlay=main_w-overlay_w-30:main_h-overlay_h-10 -profile:v main -level 3.1 -ar 44100 -b:a 160k -crf 20 -s 720x1280 -vcodec h264 -vsync 2 -acodec aac -movflags +faststart /storage/emulated/0/Movies/RMR/out.mp4

  I’m using -vsync to drop duplicated frames. This is not good enough, video is with freezing frames. How can I prevent freezing ?

• Two pass high quality theora/vorbis ffmpeg encoding

  25 septembre 2017, par Lea Chescotta

  I want to achieve the same video encoding that I had with ffmpeg2theora with standard ffmpeg, this is because i need the flexibility ffmpeg has to make the container mkv, with subtitles other than srt.

  In ffmpeg2theora i have the following command that output a very high quality and very small filesize file :

  $ ffmpeg2theora --videobitrate 2000 --two-pass --first-pass firstpass --speedlevel 0 --width 640 --height 360 --resize-method lanczos --noaudio input.mkv
  
  $ ffmpeg2theora --videobitrate 2000 --two-pass --second-pass firstpass --speedlevel 0 --width 640 --height 360 --resize-method lanczos --noaudio input.mkv --output output.ogv

  Being the most interesting options here i think (From ffmpeg2theora manual page) :

  --two-pass
  
  --first-pass <filename>
  
  --second-pass <filename> 
  
  --speedlevel
  
      encoding is faster with higher values the cost is quality and bandwidth (default 1)
  
  </filename></filename>

  But i can only found a simple way to encode theora/vorbis in standard ffmpeg (from : https://trac.ffmpeg.org/wiki/TheoraVorbisEncodingGuide) :

  ffmpeg -i input.mkv -codec:v libtheora -qscale:v 7 -codec:a libvorbis -qscale:a 5 output.ogv

  That produces a very bad quality output even in the best quality setting (10)

  How can I do a 2 pass ’high quality’/’not so big filesize’ theora/vorbis in plain ffmpeg ?

• How to encode a mp4 which has high quality,fast encode speed and low bitrate using FFmpeg API？

  8 septembre 2017, par OnlYet

  I have lots of ARGB binary data and need to encode them to a mp4 file using FFmpeg API.The most difficult things is to deal with the balance between quality,speed and bitrate.

  Below is two download links for mp4 files generated from the same ARGB data.

  • Generated through FFmpeg API : MP4 #1

  • Generated through FFmpeg command line : MP4 #2

  The mp4 generated through command line has high definition and low bitrate(745kbps) while the other has not enough high quality but high bitrate(1009kbps) I don’t know the parameters of the mp4 generated through command line but a part of my code is below :

   codec_ctx->codec_type = AVMEDIA_TYPE_VIDEO;
  
   codec_ctx->width = width;
  
   codec_ctx->height = height;
  
   codec_ctx->time_base.num = 1;
  
   codec_ctx->time_base.den = fps;
  
   stream->time_base = { 1, fps };
  
  if (!strcmp(out_fmt, "mp4"))
  
      {
  
          codec_ctx->codec_id = AV_CODEC_ID_H264;
  
          codec_ctx->bit_rate = 800 * 1000;
  
          codec_ctx->rc_max_rate = 800 * 1000;
  
          //codec_ctx->rc_min_rate = 200 * 1000;
  
          codec_ctx->rc_buffer_size = 500 * 1000;
  
          /* More gop_size less file size */
  
          codec_ctx->gop_size = 30;
  
          codec_ctx->max_b_frames = 3;
  
          /* Set relevant parameters of H264 */
  
          codec_ctx->qmin = 10;   //default 2
  
          codec_ctx->qmax = 31;   //default 31
  
          codec_ctx->max_qdiff = 4;
  
          codec_ctx->me_range = 16;   //default 0 
  
          codec_ctx->max_qdiff = 4;   //default 3 
  
          codec_ctx->qcompress = 0.6; //default 0.5
  
          ret = av_dict_set(dict, "profile", "high", 0);
  
          // Keep a balance between speed and quality when encoding
  
          ret = av_dict_set(dict, "preset", "superfast", 0);
  
          ret = av_dict_set(dict, "threads", "0", 0);
  
          ret = av_dict_set(dict, "crf", "26", 0);    
  
          // set delay time
  
          ret = av_dict_set(dict, "tune", "zerolatency", 0);
  
          return;
  
      }

  I know the parameters that affect video quality are mainly these :

  bitrate, "qp", "crf", gop_size, qmin and "preset".

  I tried to increase gop_size to decrease bitrate but mp4 quality became lower. I also found that the less crf, the more quality and the more bitrate. The less qmin,the more quality and the more bitrate. And preset a higher encode speed, the more bitrate.

  In fact, I want to set "preset" to ultrafast and set "crf" to 20 but the output mp4 will be larger.So why the mp4 generated through command line can be high quality but low bitrate ? How to set the parameters of AVCodecContext to generate a mp4 with high quality,low bitrate and high speed ?

  Supplementary notes ：
  The mp4 generated through command line stay low bitrate most of the time and higher bitrate sometimes but my mp4 is always stay relatively high bitrate. I think the point is to control the bitrate.