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• How to generate only 10 thumbnails irrespective of video duration with ffmpeg

  15 août 2022, par EaBengaluru

  Hi i want to generate only 10 thumbnails irrespective of video duration with ffmpeg

  


  I have followed this thread Create multiple thumbnails from a video at equal times / intervals

  


  here is the command i'm using

  


  ffmpeg -i input.mp4 -vf "select='not(mod(t,60/12))'" -vsync vfr output_%04d.jpg


  


  for 14.4 duration video it is generating only 3 thumbnails , i want always 10 with equal interval.

  


  For example if i have 120 duration video i must get thumbnails at

  


  [0 or 12, 24,36,48,60,72,84,96,108,120]


  


  Question : i want to generate always 10 thumbnails with equal interval as shown in example for duration of 120

  


• Mimic Audacity amplification with Pydub

  16 août 2022, par Unisionzz

  For my music library I have used Audacity for recent years to amplify the music to similar levels of loudness ; technically speaking this is not completely true, but for me it is sufficient. However, as it is tedious to do this all by hand, I decided to write a Python code to automate this process for me. The code after the imported package(s) and defined functions will run in a loop in which the filename changes depending on which song is processed.

  


  The difficult part is that I have not yet been able to find a consistent way to amplify different songs so that when the output files are put through Audacity, it will not want to change the amplitude by more than 0.1 dB(FS).

  


  Below are two attempts which seem to have come closest to the desirable output ; other methods that I have tried were either less succesfull or resulted in clipping.

  


  The first attempt finds the maximum dBFS of the song and then applies a gain in order for the maximum dBFS to equal 0 (I have also tried this method with sound.dBFS and sound.apply_gain, but results seem more mixed than the attempt below) :

  


  from pydub import AudioSegment

def change_amplitude(sound, target_dBFS):
    change_in_dBFS = target_dBFS - sound.max_dBFS
    return sound.apply_gain_stereo(change_in_dBFS)

# Audio is gathered from a hard coded path
s = AudioSegment.from_file(Dir+filename+".mp3", "mp3")
amp_s = change_amplitude(s, 0)
amp_s.export(Dir+filename+".mp3", format = "mp3")


  


  The second attempt finds the amplitude and the maximum allowable amplitude (before clipping), recalculates both to dB and then adds the dB_diff to the sound :

  


  import numpy as np
from pydub import AudioSegment

s = AudioSegment.from_file(Dir+filename+".mp3", "mp3")

# Get dB amplitude of song and maximum allowable value
dB_sound = 20*np.log10(s.max)
dB_max = 20*np.log10(s.max_possible_amplitude)
dB_diff = dB_max - dB_sound

amp_sound = s + dB_diff


  


  Summarizing, I would like to import a music file, amplify it similar to Audacity amplification and then export the file again.

  


• ffmpeg save video in segments, time does not match

  22 août 2022, par Yohann

  I use ffmpeg to save the rtsp live stream to the local, specify the fragment size of 2 seconds and use the current time to name the video file

  


  But the length of the returned video is not equal to 2 seconds and the interval between file names is not 2 seconds

  


  I have tried several command line arguments

  


  ffmpeg -i rtsp://192.168.18.119/live/test -f segment -strftime 1 -segment_time 2 -segment_atclocktime 1 -reset_timestamps 1 -an -vcodec copy ./%Y-%m-%d-%H.%M.%S.mp4

# execute result
2022-08-22-17.20.16.mp4  duration：00:03
2022-08-22-17.20.17.mp4  duration：00:03
2022-08-22-17.20.18.mp4  duration：00:07
2022-08-22-17.20.19.mp4  duration：00:03
2022-08-22-17.20.20.mp4  duration：00:03
# file names are not time aligned


  


  ffmpeg -i rtsp://192.168.18.119/live/test -f segment -strftime 1 -segment_time 2 -reset_timestamps 1 -an -vcodec copy ./%Y-%m-%d-%H.%M.%S.mp4

# execute result
2022-08-22-17.42.36.mp4 duration：00:03
2022-08-22-17.42.37.mp4 duration：00:03
2022-08-22-17.42.41.mD4 duration：00:03
2022-08-22-17.42.44.mp4 duration：00:03
2022-08-22-17.42.48.mp4 duration：00:03
2022-08-22-17.42.51.mp4 duration：00:03
# file names are not time aligned


  


  Expect to generate video

  


  2022-08-22-17.50.00.mp4 时长：00:02
2022-08-22-17.50.02.mp4 时长：00:02
2022-08-22-17.50.04.mD4 时长：00:02
2022-08-22-17.50.06.mp4 时长：00:02
2022-08-22-17.50.08.mp4 时长：00:02
2022-08-22-17.50.10.mp4 时长：00:02
...