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• nested loop in bash shell

  17 juin 2015, par Tareq Suheimat

  I want to stream video using ffserver and then receive and download it using ffmpeg but first I want to add some noise to the link using netem and the wanted noise will be Bit error,so for the transmitter side there’s no problem the problem is at the receiver side
  so the first loop must contain the percentage numbers of the bit error like 0.2 0.4 0.6 0.8 and do the following command :

  tc qdisc change dev eth0 root netem corrupt 0.1%

  then for each one of the bit error values must repeat it for 10 times and for each try I must download the received video using the following command :

  ffmpeg -i rtsp://localhost:7654/test1-rtsp.mpg -acodec copy -vcodec copy output.mp4 

  so later I end up with too many videos to compare them later.

  please people help me it’s urgent !!!

  tell now I have this scratched code but I don’t know how to compile it together

  for i in {0.2 0.4 0.6 0.8}
  
  do
  
      tc qdisc change dev eth0 root netem corrupt ${i}%
  
  
  
      #(must repeat for each i the ffmpeg download command 10 times)
  
  
  
      #The download command
  
      for x in {1..N}
  
      do
  
          ffmpeg -i rtsp://localhost:7654/test-rtsp.mpg -acodec copy -vcodec copy tested${x}.mp4
  
      done

• Add Audio to video with existing audio using FFmpeg and change volume of of both audios

  14 juin 2017, par 1234567

  Add Audio to video with existing audio using FFmpeg and change volume of both audios

  I am using this command from ffmpeg to merge audio to video

  video.mp4 has video and audio, and audio.m4a only has audio

  ffmpeg -i video.mp4 -i audio.m4a -map 0:v -map 1:a -c copy -shortest output.mp4

  I want to merge audio to video but maintain audio from both video and the new audio file

  I also want to change the volume of audio file that I want to add from current file to 1.5 times

  and change the audio from the video file to 0.5 times

  how can we change the volume and still maintain new and old audio in the merged file

• Batch mixing audio, given timestamps. Multiple offsets, only two sounds. How to do it efficiently ?

  3 août 2021, par Evil

  I have two stereo sounds, 1.wav and 2.wav, these sounds are less than 1 second long and list of timestamps (miliseconds from start of recording). Recording of pure video (recording.mp4) is several hours long and there are thousands (20 000 - 30 000) of timestamps per sounds.

  


  I want to convert list of timestamps and sounds into one recording, merging it with video. The part of merging audio with video is easy with ffmpeg, so this is not part of the question.

  


  The list of timestamps is tsv, for example :

  


  


  1201\t1.wav
  
1501\t2.wav
1603\t1.wav
  
and so on, up to 50 000

  


  


  I can convert it to anything, I am generating this file.

  


  I have seen mixing sound with padding and mixing audio to existing video, but I have to batch process a lots of samples, running sox that many times is not feasible. Mere constructing input for ffmpeg or sox is a cumbersome task.

  


  


  sox -M f2.wav f3.wav f1.wav out.wav delay 4 4 8 8 remix 1,3,5 2,4,6
  
(assuming stereo), or

  


  


  


  sox -m f1.wav "|sox f2.wav -p pad 4" "|sox f3.wav -p pad 8" out.wav

  


  


  Cool for three files. Not feasible for 50 000+. First one needs to read file multiple times (even if it is the same one) and remix channels. Second executes 50 000 sox invocations, also reading the same two files (1.wav, 2.wav) over and over.

  


  I do not use any effects on sounds. There is no explicit support in sox to take one input and play it multiple times (echo / echos destroys the material). Also creating padding or delay takes a lot of time. FFMPEG also needs long query to make it happen.

  


  Since muxing two files is easy, I have tried to record two sounds separately, but still it takes a lot of time to process.

  


  Is there simpler / faster way ?

  


  Taking advice from fdcpp, since wav is PCM coded I also consider writing C program to parse it. I will update code, when I am done.
  
This extends question : is there way to encode offsets in wav format ?