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• Can FFMPEG pause a live audio recording when db levels fall below threshold ?

  30 avril 2020, par DeepTrik

  I am in the process of converting 100's of audio cassettes to FLAC files. I have used Audacity and RecordPad by NCH Software to set decibel (dB) thresholds. so that when my devices stop and require a tape flip, the recording also pauses.

  



  I would like to move my tape playing devices (USB-based) to ubuntu 18.04 and run them on FFMPEG, but was wondering if FFMPEG had the ability to pause the recording when the audio signal falls below a configurable threshold.

  



  This helps me reduce the storage waste. Soon I have to convert some older audio reels as well in which the problem will get worse.

  



  The probe with Audacity is limited # of instances. If Audacity allowed me to instantiate multiple instances (1 for each playback device), I wouldn't be asking this question.

  



  I'm a bit of a noob to shell scripting...here is the end of my current shell script :

  



  nohup ffmpeg -nostdin -f alsa -i hw:"$DEVICE" -t $DURATION  -filter:a volumedetect -ar 48000 -ac 2 -b:a 320k "$TITLE".flac 2> "$TITLE".log &

  



  Thanks in advance !

  



  Deep

  


• How can I combine multiple bitmap frames using the ffmpeg library in cpp ?

  20 février 2021, par Evan Pacini

  Ok so I've been making a program in cpp that that a 24-bit (or less) bitmap and through checking its luminance converts it into a 1-bit bitmap, which works totally fine... However I've also been using ffmpeg in my cpp code (through the use of system()) to compile multiple frames with different luminances in order to make a video from it.

  


  //Compile to video
char cmd[168];
std::strcpy(cmd, "ffmpeg -y -framerate ");
std::strcat(cmd, framerate);
std::strcat(cmd, " -i ");
std::strcat(cmd, outFileName);
std::strcat(cmd, "/frm%d.bmp -pix_fmt yuv420p -vf \"pad=ceil(iw/2)*2:ceil(ih/2)*2\" ");
std::strcat(cmd, outFileName);
std::strcat(cmd, ".mp4");
std::system(cmd);


  


  This works fine however as bitmap is uncompressed and the number of frames can get quite large, I've been trying to improve the performance so the program takes less long to run. This is why I want to use the ffmpeg library instead of the executable, which will also make the program more portable, and hopefully, more performant.

  


  However, I find the documentation of the libraries quite intricate and the examples quite limited, as most of them explain how to extract frames from a video while I intend to compile frames into a video...

  


  So does any of you know how to do that ?

  


• avfilter/vf_blackdetect : support full-range YUV

  8 décembre 2022, par Niklas Haas

  avfilter/vf_blackdetect : support full-range YUV
  This filter currently makes the distinction between limited and full
  
  range by testing for the deprecated YUVJ pixel formats at link setup
  
  time. This is deprecated and should be improved to perform the detection
  
  based on the per-frame metadata.
  Rewrite it to calculate the black pixel threshold at the time of
  
  filtering a frame, when metadata about the frame's color range is known.
  
  Doing it this way has the small side benefit of being able to handle
  
  streams with variable metadata, and is not a meaningful performance
  
  cost.
  Signed-off-by : Niklas Haas <git@haasn.dev>
  

  • [DH] libavfilter/vf_blackdetect.c