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• ffmpeg : generate different multibitrate video from single input

  26 septembre 2016, par Stack Overflow

  I want to generate multiple multibitrate files from one single resource.

  I want to generate 4 different quality file : 240p , 360p , 720p , 1080p.

  My requirement is suppose i provide a file having 360p quality then only 2 file get generated
  1) 240p
  2) 360p

  If, I provide a file having 720p quality then 3 files get generated
  1) 240p
  2) 360p
  3) 720p

  Exactly same like youtube. (If you upload higher quality video then it provides more quality option , if you upload lower quality video then it provide less quality option).

  Is there any ffmpeg command which do same ? i.e from single input source it identify and generate multibitrate file of lower bitrate automatically.

• How to automatically detect and output audio silence with FFmpeg (or SoX) ?

  9 septembre 2018, par joshisanonymous

  I have about 100 audio files that I want to run noise reduction on via SoX, but I don’t want to manually create noise profiles for each one and I don’t know with certainty that there are X number of seconds of silence at the beginning of each one, so I’m trying to figure out how to automatically detect silence in each file and save that silence to an audio file so that I can use that to create noise profiles with SoX. FFmpeg seems like it might be able to do this, but I’m not familiar with how it works. I’ve figured out that I can use silencedetect, but that just seems to give me timestamps. I’m not sure how I might use those as the input for something that would trim the audio to just those silent portions. I’ve also thought about silenceremove, but that does the opposite of what I want, i.e. I don’t want to remove all the silence, I want to remove all the non-silence. Any suggestions ?

• how to automatically oversample and downsample when using filters ?

  4 juin 2021, par Yue Wang

  I am researching avfilters. Say I have an audio with sample rate s, and bit depth d,

  


  What I want to do is to write a graph that

  


  

  • upsample s by 4x, and set precision to 64bit float

  


  • apply some biquad filters with 64bit precision

  


  • downsample by 4x back to s, and set bit depth back to d.

  


  


  The reason to oversample is to get better filtering result by antialiasing, and the reason to downsample is to stream using the original source format.

  


  I don't know if there's way that I can do it automatically in the graph.

  


  ashowinfo could print out the sample rate, but seems there's no way to use the value later in the pipeline.

  


  asoftclip has a oversample factor. but it's not available in other filters.