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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.

  


• ffmpeg resize video then over lay on top of image using nvidia cuda

  16 mars 2021, par user72261

  i have a bunch of old family videos that are 4:3 SD format i am looking to change them to 16:9 and over lay the video on top of a 720p background

  


  i can do this fine using standard ffmpeg and everything works but it takes for ever with over 10 years of videos to convert

  


  i have a desktop pc i use for work with 2070 super installed so i was looking to use that to speed it up a little i tried adding cuda hardware support and i just hit errors

  


  ffmpeg -y -vsync 0 -hwaccel cuda -hwaccel_output_format cuda -loop 1 -i image.jpg -i video.mp4 -filter_complex "[1]hwupload_cuda,scale=1280:720:force_original_aspect_ratio=decrease[inner];[0][inner]overlay_cuda=x=10:y=10:shortest=1[out]" -map "[out]" -map 1:a -c:a aac -map 0:v -c:v  h264_nvenc -b:v 5M -y output.mp4


  


  the errors i keep getting are

  


  decoder->cvdl->cuvidDecodePicture(decoder->decoder, &ctx->pic_params) failed -> CUDA_ERROR_INVALID_IMAGE: device kernel image is invalid


  


• ffmpeg libavformat - output method

  2 octobre 2022, par Branqueira

  I have made a website that can display x camera live using rtsp.

  


  The user connects to the url, the javascript hls.js makes a request to the tomcat java server. If this is the first invocation, the code does jni to call my c code which uses ffmpeg.
In the ffmpeg part, the input is the rtsp : // url and the output is the hls + http stream which corresponds to my tomcat server. This allows to put in a buffer if there is x connection to see the ip camera.
In conclusion, there is only one ffmpeg instance running regardless of the number of people calling the html page.

  


  All this works well and for 2 years already.

  


  But I would like to improve the "machin"

  


  I would like the output of ffmpeg to always be in hls but instead of it being http, I want this to invoke a method (for example) that contains the file's buffer and its name.

  


  for that I use

  


  avformat_alloc_output_context2 (& formatOutputCtx, NULL, "hls", output_url);


  


  which allows me to select the hls + http protocol automatically

  


  I looked at the doc but couldn't find a solution using another protocol or doing one custom.

  


  If someone has an idea ? otherwise no big deal :)