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• ffmpeg and grep not working to extract mean_volume value

  31 octobre 2019, par Json

  I have a list of mp3 files and i want to set all mean_volume to the same db value using a script, so I enter the command for detecting the value (https://trac.ffmpeg.org/wiki/AudioVolume) and I try to grep the value but it fails and instead prints all the output from the ffmpeg command. Any thoughts ?
  Also tried tr instead of grep. The command I used is :

  ffmpeg -i sample.mp3 -filter:a volumedetect -f null /dev/null | grep 'mean_volume'

• Monitoring ffmpeg two-passes encoding

  31 décembre 2024, par Hodol

  I'm new in FFMPEG.

  


  According to the official guide, https://trac.ffmpeg.org/wiki/Encode/VP9 I use the following command to convert a large h.264 file :

  


  ffmpeg -i input.mp4 -c:v libvpx-vp9 -b:v 0 -crf 30 -pass 1 -an -f null /dev/null
ffmpeg -i input.mp4 -c:v libvpx-vp9 -b:v 0 -crf 30 -pass 2 -c:a libopus output.webm


  


  However, the pass-1 takes too long time and it does not log progress. With -report option I can see something is in progress but I don't know how long I should wait.

  


  Here's questions :

  


  

  1. Is there any way to see the progress of 1-pass ?

  


  2. Is there any way to speed up the process ?

  


  


  Thank you,

  


• ffmpeg audio synch issue - fractional framerate

  29 mars 2013, par JoeCitizen

  We are working on an Android app which uses the ffmpeg library via JNI to edit the frames of a video while keeping size, codec etc the same.

  We are having an issue where the audio of the output video is getting out of sync with the video. We believe this is because some input videos have a frame rate which isn't a whole number e.g 25.66 fps and our output will be at 25fps. We have tried to change the time_base field of the output codec to keep the precision i.e by multiply the numerator and denominator but it makes the output frame rate ridiculously high.

  Does anyone know how to force ffmpeg to use the exact same output frame rate as the one it reads in ? We have not found a way to output videos with a fractional frame rate.

  Example of setting up the output codec :

      c =                 st->codec;
  
      c->codec_id =       codec_id;
  
      c->codec_type =     AVMEDIA_TYPE_VIDEO;
  
      c->bit_rate =       inputCodecCtx->bit_rate;
  
      c->width =          inputCodecCtx->width;
  
      c->height =         inputCodecCtx->height;
  
  
  
      c->time_base.num =   1000;
  
      c->time_base.den =  (int)(fps*1000);//fps of the input video *1000 to keep precision
  
  
  
      c->gop_size =       inputCodecCtx->gop_size;
  
      c->pix_fmt =        inputCodecCtx->pix_fmt;
  
  
  
  
  
  
  
      static int write_video_frame(AVFormatContext *oc, AVStream *st, AVFrame *newpict, double fps)
  
      {
  
          int             ret = 0;
  
          AVCodecContext* c = st->codec;
  
  
  
          AVPacket pkt;
  
          av_init_packet(&pkt);
  
  
  
          if (pkt.pts != AV_NOPTS_VALUE)
  
          {
  
              pkt.pts =  av_rescale_q(c->coded_frame->pts, c->time_base, st->time_base);
  
  
  
          }
  
          if (pkt.dts != AV_NOPTS_VALUE)
  
  
  
  
  
          {
  
              pkt.dts = av_rescale_q(c->coded_frame->pts, c->time_base, st->time_base);
  
          }
  
  
  
  .....
  
  }