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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.

  


• Aspect ratio problems at transcoding with ffmpeg [closed]

  19 novembre 2023, par udippel

  I have a huge collection of videos from the last 20+ years, videos in all sorts of formats. I use gerbera as open source UPnP-AV media server. Our TV handles only very limited of these formats. Therefore I use the transcoding feature of gerbera (I don't want to convert the 2000+ files ; thereby avoiding loss of multiple audio tracks, (multiple) subtitles, and so forth).

  


  This is my current unified argument line for ffmpeg :
-c:v mpeg2video -maxrate 20000k -vf setdar=16/9 -r 24000/1001 -qscale:v 4 -top 1 -c:a mp2 -f mpeg -y
It works pretty okay, except of the aspect ratios. Well, I don't understand this fully, because ffprobe for File A states :
Stream #0:0: Video: mpeg4 (Simple Profile) (XVID / 0x44495658), yuv420p, 624x464 [SAR 1:1 DAR 39:29], 1500 kb/s, 25 fps, 25 tbr, 25 tbn, 25 tbc
This file displays very well.
File B comes as :
Stream #0:0(eng): Video: h264 (High), yuv420p(tv, bt709, progressive), 960x720, SAR 1:1 DAR 4:3, 23.98 fps, 23.98 tbr, 1k tbn, 180k tbc (default)
This file displays horribly squeezed vertically and doesn't fill the screen left and right neither, with the same settings of the TV. Also, playing this file (and others, naturally) the TV doesn't offer the 14:9 display option, which is available e.g. for the file further up.

  


  Both have same SAR, DAR, almost identical H:V ratios (1.345, 1.333) ; and almost identical DAR.

  


  My questions :

  


  

  1. Why, despite of almost identical pixel ratios, DAR and SAR are these files handled so differently in one and the same session on the same TV (SONY), please ?

  


  2. With which method could I instruct ffmpeg to display the second file properly, too, please ?
(I have already tried 'scale' ; but to no avail. Which could have been foreseen, since the ratios are already very close.)
My guess is, that the (tv, bt709, progressive) mess things up.
(I have already tried to add the yuv420p in the argument line, also to no avail.)

  


  


  Appreciate any help,

  


  Uwe

  


  I have already tried to add a 'scale' option ; but to no avail. Which could have been foreseen, since the ratios are already very close.
I have already tried to add the yuv420p in the argument line, also to no avail.
I have already tried force_original_aspect_ratio, but also here, nothing improving.
Also, I played with -aspect, but the aspects are okay, and would need individual corrections, which I can't and don't to do for 2000+ files. A simple 16:9 doesn't cut it.

  


• Creating an ffmpeg html/php form process and need ffmpeg technical feedback

  7 juin 2016, par dave

  I have decided to create an input form for ffmpeg to go with my video uploader.

  This is for my video uploader plugin for a social site software. Users have told me that they want technical options for videos so they can choose the specific options they want including thumbnail options.

  I have been reading the ffmpeg docs most of the morning as well as watching some videos and i have come up with a rough draft of my form. The videos uploaded will more than likely be non gaming, personal and hobby videos.

  The goal here is to have a form that is easy enough for the non technical user, but technical for those that want the options. So i do plan to have a checkbox which allows the non technical user to skip the technical settings. This will result in a generic ffmpeg command with default settings. If they choose to use the technical specs then it will create a more specific ffmpeg command stream.

  here is what i have so far in the draft.

  select max size options ’50MB’,’100MB’,’200MB’,’500MB’,’650MB’,’750MB’,’1GB’,’2GB’,’3GB’

  input for thumbcapture in seconds maxlength 2 size 2

  input for video in ’mpg’,’wma’,’mov’,’flv’,’mp4’,’avi’,’qt’,’wmv’,’rm’

  option for video size ’200x100’,’320x240’,’560x315’,’640x360’,’853x480’,’1280x720’ not sure if i want to offer a custom slot or not.

  my thought here is that if they do not want the tech version of the form then the codecs will be b:v copy b:a copy (if that is the smart way to do it) or just left out and let ffmpeg decide what is best.

  ===== this is the technical part of the form =======

  select for acodec options copy, mp3, mp1, mp2, dnet, 28_8, wmav2, alac, cook

  select for vcodec option copy, ffv1, ms-cram, mpeg-4, rv40, wmv, xvid, mov, qt, avchd

  select for bitrate audio 32k, 64k, 128k

  select for bitrate video 1000k, 1200k, 1500k

  select for sampling rate 22050, 44100

  input for crf(mp4 out only) size 2 maxlength 2 minval 2 maxval 49

  input for avi quantanizer (avi out only) size 2 maxlength 2 minval 2 maxval 49

  ===== end technical form =====================

  select for video out ’avi’,’mp4’,’flv’

  that is what i have so far. How does that combination on the technical side look to you ffmpeg pros ?

  Any suggestions ? :)