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• Retune FLAC compression levels

  20 octobre 2014, par Martijn van Beurden

  Retune FLAC compression levels
  This patch changes a the settings associated with compression
  
  levels 6, 7 and 8. With this patch, -e is no longer used, but
  
  instead apodization functions are added. This should improve
  
  compression with at least 95% of all material while not changing
  
  the speed much. Decoding ways, 6 and 8 stay the same, and 7 is
  
  slowed a bit, which makes it as fast as 8.
  Signed-off-by : Erik de Castro Lopo <erikd@mega-nerd.com>
  

  • [DH] src/libFLAC/stream_encoder.c

• ffmpeg zoompan multiple zoomin/zoomout on different areas of big image [closed]

  10 janvier 2024, par LinuxAdmin

  I need to create a video, with zooming in and out different areas of one big square image.
I tried different zoompan examples, but can't do what I want. What I resolved is keeping aspect ratio of square image, setting setsar=ratio='(1/1)' before zoompan and setdar=ratio='(1/1) after.

  


  Video begins with full image (keeping aspect ratio), then zooms in to a sector of image (1sec), stay 1 second, and zoomout back to full size (1sec). I have 40 sectors, all same size. I can iterate every with bash, adding zoompan line for every sector, setting right x/y coordinates.

  


  Please help me evaluate zoompan expression for getting such result.

  


• 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.