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• OpenCV video writing to named pipe

  21 janvier 2012, par user28667

  I'm trying to send videos created with OpenCV in real-time to user though Apache (user downloads video from a website). I don't need streaming video. I'm just trying to transfer whole video file. My OpenCV program writes video to a named pipe (created with mkfifo) and PHP scrpt reads from it and outputs to user.

  The problem is that pipe-transfered videos doesn't open in Windows. They're shorter exactly at 7072 bytes (checked with different videos). They are not just truncated. The first difference between videos appeared in 5-th byte. And there is no mistake in PHP script. I've checked it using :

  cat fifo.avi > output.avi

  The result was the same. How to make OpenCV write videos to pipes just as to normal files ? Why this happens ? Or is there another way to send videos in real-time to user ?

  P. S. Thanks and sorry for bad English
  P. P. S. I'm creating CvVideoWriter with this code if it matters :

  cvCreateVideoWriter("fifo.avi",CV_FOURCC('M','J','P','G'),25,cvSize(blah blah blah),1)

• ffmpeg : "Impossible to convert between the formats" when using NVIDIA GPU hardware acceleration

  24 mai 2021, par MorenoGentili

  I'm using ffmpeg from the command line on Windows 10 and I wanted to gave GPU acceleration a try to improve execution times. A simple cut command like this works fine and its execution time is reduced by 60-70%. Awesome.

  


  ffmpeg -hwaccel cuvid -c:v h264_cuvid -ss 00:00:10 -i in.mp4 -c:v h264_nvenc out.mp4


  


  Now I tried to use the -filter_complex flag to overlay, fade and translate a png image over a video. The working non-GPU enhanced command is this one :

  


  ffmpeg -i in.mp4 -loop 1 -t 75 -i overlay.png -filter_complex "[1:v]fade=t=in:st=30:d=0.3:alpha=1,fade=t=out:st=35.7:d=0.3:alpha=1[png1];[0:v][png1]overlay=x='if(gte(t,30), (t-30)*10, NAN)'" -movflags +faststart out.mp4


  


  Then, I added the GPU-related flags to the command like this.

  


  ffmpeg -hwaccel cuvid -c:v h264_cuvid -i in.mp4 -loop 1 -t 75 -i overlay.png -filter_complex "[1:v]fade=t=in:st=30:d=0.3:alpha=1,fade=t=out:st=35.7:d=0.3:alpha=1[png1];[0:v][png1]overlay=x='if(gte(t,30), 60-tanh((t-30)*30/5)*60, NAN)'" -movflags +faststart -c:v h264_nvenc out.mp4


  


  But it won't work. I get this error.

  


  Impossible to convert between the formats supported by the filter 'graph 0 input from stream 0:0' and the filter 'auto_scaler_0'
Error reinitializing filters!
Failed to inject frame into filter network: Function not implemented
Error while processing the decoded data for stream #0:0


  


  I don't even know what it means. Can I actually run ANY ffmpeg command on the GPU with GPU acceleration ? I've found some information about the hwupload_cuda flag but I'm not sure if I should use it and how. My attempts have failed so far.

  


  Any advice on how I should modify the command to make it work on the GPU ?

  


• Stacking 3 gmp4-files using Avisynth and VirtualDub, results in wrong colors and distorted files

  22 juin 2015, par Frederik Amann

  I need to conduct the seemingly simple task of stacking 3 files next to each other. They are all the same : .avi Container, 320x240, 4:3, 25 fps, GeoVision Advanced MPEG-4 GEO codec.
  I installed the GeoVision codec (http://www.geovision.com.tw/english/5_8.asp# - select "other utilities"), so my system (windows media player, media player classic) can play back the files. Also, I can open and work with them in Virtual Dub. I installed AviSynth and wrote the simple script for stacking them next to each other

  h1 = AVISource("Event20150423075842001.avi")
  
  
  
  h2 = AVISource("Event20150423075842002.avi")
  
  
  
  h3 = AVISource("Event20150423075848003.avi")
  
  
  
  StackHorizontal(h1, h2, h3)

  now, when I save it as .avs and then open it using VirtualDub, I see three videos nicely put next to each other, but the colors are weird and parts of the video are upside down and everything is just ..wrong - see Screenshot http://www.linkfile.de/download-46f71057ed130f9be29510f68ce4ee71.php. First I thought it has something to do with avisynth taking the wrong codec, so i forced it on gmp4 (as you can also see in the screenshot), but the result is the same. I have now also Avisynth+ installed, as well as VirtualDubMod.
  When I open the .avs in VDMod, I get "couldn’t locate decompressor for format YV24", but it still opens the video which looks a little better though (but when I make a direct stream copy and save it, then play it back in MPC it looks exactly the same as it looked on the first screenshot). So this error points me toward something related to the colorspace.
  Now my questions :

  • How can I find out in which format my files are ? YUV24, YUV12, ..?
  • And then, how can I tell Avisynth to use a format that VirtualDubMod can deal with ?
  • Or how can I make VirtualDub deal with YUV24 ? Am I just missing a codec ? Is my train of thought even slightly on the right track, or is my problem something totally different ?

  I also found this related thread : Editing/Decoding AVI files using system-installed proprietary codecs, but using avisynth and ffmpeg, I get similar results as with VirtualDub.

  I can’t use the solution of converting all my files first and then do the stacking in a second step - because the actual files I have to work with are about 180 videos, each like 8hours long and the time it would consume would stand in no relation to my possibilities..

  I really have looked for solutions during the past week, and I think I’m close, but I sadly just don’t know enough about programming to be able to solve it on my own.. so I also want to excuse for any apparent stupidities in my explanation ;)
  I’m very thankfull for any help

  Have a good time everybody

  EDIT :
  So I have some more Info, and an example file, which I can’t link in this post -.- because I -again- have not enough reputation, very nice. I will try to comment and post the links :)

  Here is what the info() command brought me :
  Colorspace : YV24,
  FieldBased (Separated) Video : NO,
  Parity : Bottom Field First,
  Video Pitch : 320 bytes,
  Audio : NO,
  CPU detected : x87 MMX ISSE SSE4.1 SSSE3