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• How to combine software and hardware video filters in FFmpeg, e.g. using CUDA/nvenc ? [closed]

  3 novembre 2020, par bemo

  One function of my Windows software project requires capturing video at 100fps for 10 seconds simultaneously from 4 machine vision cameras. I'm initially storing the video data in uncompressed/raw video files, one per camera, where these files are just concatenated raw frame data from the camera (in Bayer rggb8 format).

  


  After capturing, I need to convert these into a compressed format (I don't do this at the time of capture to avoid clogging up the CPU and minimise the risk of dropping frames). I'm using ffmpeg for this and I've arrived at this command that gives satisfactory results :

  


  ffmpeg.exe -y -an -f rawvideo -pixel_format bayer_rggb8 -video_size 2048x1536 -framerate 100 -i input.raw -codec:v libx264 -preset medium -crf 17 -vf "vignette=mode=backward:a=PI/7,lenscorrection=k1=-0.14,unsharp=13:13:1.5:5:5:0,hqdn3d,format=yuv420p" output.mp4

  


  Since the above uses software encoding it is pretty slow and takes several minutes to complete the 4x10s videos. I need it to be a lot faster to avoid the user having to wait too long within my app for transcoding to finish. So, I want to speed this up using ffmpeg's hardware acceleration.

  


  I've purchased a nvenc/CUDA-compatible GeForce card, have compiled ffmpeg with CUDA support and have experimented with the h264_nvenc encoder. Basic encoding works (without encoding parameters and filters) but I've got two specific problems :

  


  

  1. -crf (and possibly -present) aren't supported by h264_nvenc, so what is the hardware-accelerated equivalent to -preset medium -crf 17 ?

  


  2. How can I apply filters to reduce vignetting, correct lens distortion (2 cameras are using fish-eye lenses), sharpen the images and then de-noise them, whilst still significantly improving overall encoding speed ? I understand some filters aren't supported by hardware so I need to use hwupload_cuda and hwdownload to move data between video memory and main memory, but I can't get the exact encoding incantation working and I'm also worried I'll lose all the hardware-acceleration benefit if I have to do too much in software.

  


  


  I'm open to using alternatives to nvenc if necessary - e.g. VAAPI, libmfx/QuickSync or OpenCL as mentioned on ffmpeg's hardware acceleration page.

  


• How to split ffmpeg output into multiple files ?

  15 novembre 2020, par Genius Billionaire

  What I want to happen : the equivalent of this : split -n 4 output.mp4, which generates 4 files. Only the first file is "valid mp4" that you can play. The other 3 files rely on the previous file.

  


  A similar request can be seen here : https://lists.ffmpeg.org/pipermail/ffmpeg-user/2013-May/015090.html

  


  Why I want this to happen : running FFMPEG in the browser, which means 1) file size limit, 2) I don't have the Linux command split to help me out, just FFMPEG. If I can get FFMPEG to output files of X MB each, I can iteratively delete files as soon as I've read them.

  


  EDIT : as a commenter asked, yes it is possible to run several ffmpeg commands if necessary.

  


  The right solution is not using segments. The following example command generates several 4 valid mp4 files. That's not exactly what I want.
ffmpeg -i ../flv.flv -segment_time 5 -f segment -t 20 %d.mp4

  


  This other solution also does not work (it's the same output as previous incorrect solution) :

  


  ffmpeg -i ../flv.flv -ss 00:00:00 -t 5 1.mp4

  


  ffmpeg -i ../flv.flv -ss 00:00:05 -t 5 2.mp4

  


• How to use sexagesimal syntax in arguments of FFmpeg or if impossible how to convert it in Windows CMD shell

  6 décembre 2020, par Link-akro

  Question updated 2020-12-06 to enlarge the scope without discarding the prior answer which applies to both prior and larger cases.

  


  I had trouble to provide a sexagesimal time (HH:MM:SS.mm) to a filter option that was not an expression. For instance trim filter.
It happens there is an escaping rule i did not know yet when i first asked, and was addressed in the first comment by @Gyan.

  


  The problem is universal, but the solution may depend on the shell if we go the scripting route... and i am currently stuck with Windows's CMD.exe.

  


  For instance the following skips one minute and 4 tenths of seconds in all streams as accurately as it can seek each, then invokes the trim filter to keep the segment between one and two minutes of the remaining duration, and do so with two different syntaxes. This example happens to be compatible with both CMD and BASH shells so no escaping hell.

  


  ffmpeg -ss "1:00.4" -i INPUT -vf "trim=start='1\:00':end='120'" OUTPUT


  


  Then how do we achieve the same in the expressions within the filters ?
If we cannot avoid using the scripting of the shell, i am looking for a Windows CMD solution.
I had posted one answer with a piece of script to convert a textual sexagesimal time to a textual decimal fractional time in seconds, which was not useful for the original case, but may apply to more generic cases and in particular to the expressions.

  


  Example of failed attempt with one expression in the select filter.

  


  ffmpeg -ss "1:00.4" -i INPUT -vf "select='between(t,1\:00',120)'" OUTPUT


  


  The sexagesimal notation seems to not be supported by ffmpeg filter expressions as i found no reference of it in the documentation nor in SO/web.

  


  I browsed through the list of functions defined in ffmpeg expression library but did not find any way to parse the sexagesimal input there yet, nor any way to use text in its semantics.

  


  However i found some unrelated example that hard-coded some arithmetical expression to provide the numerical decimal amount of seconds equivalent to what was intended, such as 2*60+2 to mean 2:02.

  


  The polynome used above to compute seconds may use preprocessing of shell variable, whichever shell it is, but we need to parse the components of HH:MM:SS.mm to put them in those variable first. You know, using bash $var or cmd %var%/%~1 styles. Otherwise we may compute the polynome completely in the shell instead of the expression but it is so much trouble for little gain.

  


  So while CMD still exists like an undead and becomes really dead , and while i do not have the opportunity yet to replace it, i wish for an answer that either :

  


  

  • does not need the shell/script at all, OR

  


  • provide a solution in Windows CMD, although relying on it as little as possible.

  


  


  Reminder and clarification, the use case assumes that we are given a textual sexagesimal time as input and intend to use it in an expression of ffmpeg filter with as little shell dependency as possible or otherwise satisfy Windows CMD.