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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.

  


• select frame of choice for thumbnail in ffmpeg

  1er octobre 2014, par Rks Rock

  Description

  I have successfully installed and used ffmpeg in my project ... I am able to create thumbnails by selecting a frame at X seconds... But that is not enough what if at X seconds there is a blacked out scene in the video or some scene that does not justify what the video is about ..

  So is there a way that I can make a UI that will give the user to select the frame lets say using a track-bar so that user can drag the track bar to a specific frame and select it as a thumbnail like a poster...

  Any one done that ??

• how to generate frames using ffmpeg `select` filter with custom function

  14 février 2023, par Ricky

  I got a video, and want to generate some frames to be my video cover candidates which should satisfied with some conditions below :

  


  

  1. frame in vary scenes.

  


  2. frame contain person with good look, no eyes closed and etc.

  


  


  I found ffmpeg select filter abilities, like

  


  ffmpeg -i input.mp4 -vf "select=gt(scene\,0.4)" -frames:v 5 -vsync vfr frames-diff-%02d.png


  


  can generate frames that have more than 40% scene change compared to the previous frames.

  


  I just found that only built-in select expressions support and no customization support.

  


  

  1. Does ffmpeg support external function/api/local command/script to give a frame select evaluation ?

  


  2. Is there any other solutions to complete my goal ?

  


  


  Thanks.