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• How to read realtime microphone audio volume in python and ffmpeg or similar

  1er septembre 2023, par Ryan Martin

  I'm trying to read, in near-realtime, the volume coming from the audio of a USB microphone in Python.

  


  I have the pieces, but can't figure out how to put it together.

  


  If I already have a .wav file, I can pretty simply read it using wavefile :

  


  from wavefile import WaveReader

with WaveReader("/Users/rmartin/audio.wav") as r:
    for data in r.read_iter(size=512):
        left_channel = data[0]
        volume = np.linalg.norm(left_channel)
        print(volume)


  


  This works great, but I want to process the audio from the microphone in real-time, not from a file.

  


  So my thought was to use something like ffmpeg to PIPE the real-time output into WaveReader, but my Byte knowledge is somewhat lacking.

  


  import subprocess
import numpy as np

command = ["/usr/local/bin/ffmpeg",
            '-f', 'avfoundation',
            '-i', ':2',
            '-t', '5',
            '-ar', '11025',
            '-ac', '1',
            '-acodec','aac', '-']

pipe = subprocess.Popen(command, stdout=subprocess.PIPE, bufsize=10**8)
stdout_data = pipe.stdout.read()
audio_array = np.fromstring(stdout_data, dtype="int16")

print audio_array


  


  That looks pretty, but it doesn't do much. It fails with a [NULL @ 0x7ff640016600] Unable to find a suitable output format for 'pipe:' error.

  


  I assume this is a fairly simple thing to do given that I only need to check the audio for volume levels.

  


  Anyone know how to accomplish this simply ? FFMPEG isn't a requirement, but it does need to work on OSX & Linux.

  


• Can speex be packed into mpegts stream ?

  24 juillet 2013, par user2384001

  I want to use speex in a real-time application. I want to playback this mpegts stream by ffmpeg. Are there any means to pack speex into mpegts stream ?

• ffmpeg copy stream preserving FPS

  10 mars 2017, par James Taylor

  I have a stream that I know is outputting at a certain frame rate (30 FPS). I want to use ffmpeg to make a copy of this stream and save it to disk.

  I have the following command :

  ffmpeg -i http://input/ -c copy -map 0 \
  
      -f segment -strftime 1 -segment_time 900 \
  
      -segment_atclocktime 1 -segment_format mp4 %Y-%m-%d_%H-%M-%S.mp4

  But when I run the command, I see the following :

  frame=   32 fps=3.9 q=-1.0 Lsize=N/A time=00:00:01.27 bitrate=N/A

  Where it appears the FPS is hovers around 4.0 FPS and time moves slower than real time.

  I tried added -re (copy the rate of the input stream) and -r 30 (manually set the rate to 30 FPS) flag specified before the input file, but it didn’t seem to work.

  I also read a similar question here using -framerate 30, but that option doesn’t exist in the man pages and is an Invalid option.

  Any help would be greatly appreciated !

  ---

  So I let the modified command (removing the flags -c copy -map 0) run for exactly 5 minutes. Running ffprobe yields :

  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '2017-03-10_01-09-12.mp4':
  
    Metadata:
  
      major_brand     : isom
  
      minor_version   : 512
  
      compatible_brands: isomiso2avc1mp41
  
      encoder         : Lavf57.2.100
  
    Duration: 00:00:15.43, start: 0.066016, bitrate: 13416 kb/s
  
      Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuvj420p(pc), 1024x768, 13414 kb/s, 30 fps, 30 tbr, 15360 tbn, 60 tbc (default)
  
      Metadata:
  
        handler_name    : VideoHandler

  Again, this only produces 15 seconds of video and I can’t seem to get a 1:1 relationship between the input stream of 30 FPS and an output stream also in 30 FPS in real time. Playing the video yields something that’s sped up.