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• Using an actual audio recording to filter out noise from a video

  9 mars 2021, par user2751530

  I use my laptop (Ubuntu 18.04 LTS derivative on a Dell XPS13) for recording videos (these are just narrated presentations) using OBS. After a presentation is done (.flv format), I process it using ffmpeg using filters that try to reduce background noise, reduce the size of the video, change encoding to .mp4, insert a watermark, etc. Over several months, this system has worked well.

  


  However, my laptop is now beginning to show its age (it is 4 years old). That means that the fan becomes loud - loud enough to notice in a recording, not loud enough to notice when you are working. So, even after filtering for low frequency in ffmpeg, there are clicking and other type of sounds that are left in the video. I am a scientist, though not an audio/video expert. So, I was thinking - is it possible for me to simply record the noise coming out of my machine when I am not presenting, and then use that recording to filter out the noise that my machine makes during the presentation ?

  


  Blanket approaches like filtering out certain ranges of the audio spectrum, etc. are unlikely to work, as the power spectrum of the noise likely has many peaks, and these are likely to extend into human voice range as well (I can hear them). Further, this is a moving target - the laptop is aging and in any case, the amount and type of noise it makes depends on the load and how long it has been on. Algorithm :

  


  

  1. Record actual computer noise (with the added bonus of background noise) while I am not recording. Ideally, just before starting to record the presentation. This could take the form of a 1-2 minute audio sample.

  


  2. Record the presentation on OBS.

  


  3. Use 1 as a filter to get rid of noise in 2. I imagine it would involve doing a Fourier analysis of 1, and then removing those peaks from the spectrum of 2 at each time epoch.

  


  


  I have looked into sox, which is what people somewhat flippantly point you to without giving any details. I do not know how to separate out audio channels from a video and then interleave them back together (not an expert on the software here). Other than RTFM, is there any helpful advice anyone could offer ? I have searched, but have not been able to find a HOWTO. I expect that that is probably the fault of my search since I refuse to believe that this is a new idea - it is a standard method used in many fields to get rid of noise, including astronomy.

  


• How to implement multiple video resolutions on front and back-end

  25 février 2021, par LanGuu

  I need a solution or hint on how should I handle multiple resolutions on front-end and back-end. I have been reading about hls, dash, and mse for last few days but the more information I read, the more lost I am.

  


  Right now I have only a microservice for downscaling video using FFmpeg. The FFmpeg returns mp4 with no hls or dash, 4 video resolutions with no sound, and 2 different audio quality.
On front-end, I use react-player. The hardest part is that I need to merge audio and video, synchronize and handle change quality events.
I have found Media source extensions but it won't work I am not sure, but probably because I am using raw mp4 files.

  


  I would like to ask you a few questions

  


  

  1. It is possible to combine video and audio sources without MSE and still keep video and audio separate

  


  2. Do I need HLS or Dash to use MSE ?

  


  3. What is a difference between progressive download and progressive streaming ?

  


  4. If I have to choose what is better right now hls or dash ? what is much easier to implement ?

  


  


• avcodec/siren : Increase noise category 5 and 6

  24 décembre 2020, par Michael Niedermayer

  avcodec/siren : Increase noise category 5 and 6
  The entry read is not used in subsequent computation, thus its
  
  value is not important.
  Fixes : out of array read
  
  Fixes : 28578/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_SIREN_fuzzer-6332019122503680
  Found-by : continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
  
  Signed-off-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] libavcodec/siren.c