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• Is there a way to (automatically) detect if the channels of a stereo video/audio are out of phase and canceling each other ?

  8 mars 2024, par Rhenan Bartels

  Background

  


  I've encountered an issue while attempting to convert an audio downloaded from a youtube video into a mono .wav format using ffmpeg. Despite using typical conversion commands (code below), the resulting audio is either silent or corrupted, indicating potential stereo channel cancellation.
I tried to load the audio into Python and calculate phase and cross-correlation, but this step uses a lot of memory, especially for a 6-hour-long audio.

  


  Goal

  


  I'm seeking a method, preferably using ffmpeg, to detect if stereo channels are canceling each other out due to phase misalignment. Additionally, I aim to automate the process of phase inversion before converting to mono to ensure the integrity of the resulting audio.

  


  Question :

  


  How can I automatically detect if stereo channels are canceling each other and subsequently invert the phase to ensure successful conversion to mono using ffmpeg ? Any insights, solutions, or alternative approaches would be greatly appreciated.

  


  Steps Taken :

  


  

  1. Downloaded audio from YouTube using yt-dlp.

  


  2. Attempted audio conversion to mono using ffmpeg, resulting in silent or corrupted output.

  


  3. Successfully converted audio to mono by manually inverting the phase of one channel prior to conversion.

  


  


  Download audio from youtube

  


  yt-dlp -f bestaudio https://www.youtube.com/watch?v=s3QB_rJzH08 -o input.webm


  


  Audio conversion

  


  The resulting file is silent or corrupted

  


  ffmpeg -i input.webm  -ac 1 -ar 16000 -c:a pcm_s16le output.wav


  


  Audio conversion to mono .wav with phase inversion

  


  The resulting file has audio

  


  ffmpeg -i input.webm -af "aeval=val(0)|-val(1)" -ac 1 -ar 16000 -c:a pcm_s16le output.wav


  


• How to Save an Image (Current Frame) from an RTSP, using FFMPEG ?

  4 mars 2023, par spaceman

  I recently purchased a Security Camera,
  
and it provides an RTSP URL withwhich you can view the video.

  


  So If I run the command VLC rtsp://<ip>/etc</ip> for example,
  
then I am successfully able to watch the stream from the camera.

  


  My question is :
  
Does FFMPEG provide some command line operation for Saving one Image from an RTSP Stream to disk ?

  


  That way I can run this command, and have a .PNG or .JPG file created on disk.

  


• Restream with FFmpeg [closed]

  30 mars, par boyuna1720

  I have iptv playlist file with inside VODs and Channel links. I want to restream it from my server becouse provider allows only one user to watch. When i am using Nginx with RTMP and FFmpeG i am getting this error. please tell me if anyone can help to fix this issue.

  


  ffmpeg -re -i "http://excel90095.cdn-akm.me:80/23a9a158d8d8/2dd736a985/325973" -c:v copy -c:a aac -f flv "rtmp ://localhost/live/test"