Recherche avancée

Sur d’autres sites (6647)

• How to extract motion vectors from h264 without a full decode on the CPU

  25 septembre 2020, par Adrian May

  I'm trying to use my nose as a pointing device. The plan is to encode the video stream from a webcam pointed at my face as h264 or the like, get the motion vectors, cook the numbers a bit and chuck them into /dev/uinput to make the mouse pointer move about. The uinput bit was easy.

  


  This has to work with zero discernable latency. This, for instance :

  


  #!/bin/bash
[ -p pipe.mkv ] || mkfifo pipe.mkv
ffmpeg -y -rtbufsize 1M -s 640x360 -vcodec mjpeg -i /dev/video0 -c h264_nvenc pipe.mkv &
ffplay -flags2 +export_mvs -vf codecview=mv=pf+bf+bb pipe.mkv


  


  shows that the vectors are there but with a latency of several seconds which is unusable in a mouse. I know that the first ffmpeg step is working very fast by using the GPU, so either the pipe or the h264 decode in the second step is introducing the latency.

  


  I tried MV Tractus (same as mpegflow I think) in a similar pipe arrangement and it was also very slow. They do a full h264 decode on the CPU and I think that's the problem cos I can see them imposing a lot of load on one CPU. If the pipe had caused the delay by buffering badly then the CPU wouldn't have been loaded. I guess ffplay also did the decoding on the CPU and I couldn't persuade it not to, but it only wants to draw arrows which are no use to me.

  


  I think there are several approaches, and I'd like advice on which would be best, or if there's something even better I don't know about. I could :

  


  

  • Decode in hardware and get the motion vectors. So far this has failed. I tried combining ffmpeg's extract_mvs.c and hw_decode.c samples but no motion vectors turn up. vdpau is the only decoder I got working on my linux box. I have a nvidia gpu.

  


  • Do a minimal parse of the h264 to fish out the motion vectors only, ignoring all the other data. I think this would mean putting some kind of "motion only" option in libav's parser, but I'm not at all familiar with that code.

  


  • Find some other h264 parsing library that has said option and also unpacks the container.

  


  • Forget about hardware accelerated encoding and use a stripped down encoder to make only the motion vectors on either CPU or GPU. I suspect this would be slow cos I think calculating the motion vectors is the hardest part of the algorithm.

  


  


  I'm tending towards the second option but I need some help figuring out where in the libav code to do it.

  


• how to create video from ffmpeg ?

  4 mai 2020, par Hong

  I have 10 images, 2 videos(mov, mp4) and 1 audio.

  



  My plan is

  



  

  1. create images to video (images.mp4)

  


  



  ffmpeg -framerate 0.75 -pattern_type glob -i '*.png' \
 -c:v libx264 -vf "format=yuv420p,pad=ceil(iw/2)*2:ceil(ih/2)*2" -r 30 -pix_fmt yuv420p out.mp4  


  



  

  2. concat videos
filelist :

  


  



  file 'images.mp4'
file 'video1.mov'
file 'video2.mp4'


  



  2-1 )
ffmpeg -f concat -safe 0 -i filelist.txt -auto_convert 1 -c copy output.mp4

  



  2-2 ) first. i'm encode mov to mp4. and change filelist.txt

  



  file 'images.mp4'
file 'video1.mp4'
file 'video2.mp4'
ffmpeg -f concat -safe 0 -i filelist.txt -auto_convert 1 -c copy output.mp4


  



  

  3. add background music.
It has not yet reached this stage.
It's blocked in plan 2.

  


  



  this plan is right ?
I'm not sure about this plan.

  



  Step 2 output is strange.
The frame of the video No. 1 and No. 2 is not smooth.

  



  How can I create video from images and meger another video.

  


• Mute parts of Wave file using Python/FFMPEG/Pydub

  20 avril 2020, par Adil Azeem

  I am new to Python, please bear with me. I have been able to get so far with the help of Google/StackOverflow and youtube :). So I have a long (2 hours) *.wav file. I want to mute certain parts of that file. I have all of those [start], [stop] timestamps in the "Timestamps.txt" file in seconds. Like this :

  



     0001.000 0003.000
   0744.096 0747.096
   0749.003 0750.653
   0750.934 0753.170
   0753.210 0754.990
   0756.075 0759.075
   0760.096 0763.096
   0810.016 0811.016
   0815.849 0816.849


  



  What I have been able to do is read the file and isolate each tuple. I have just output the first tuple and printed it to check if everything looks good. It seems that the isolation of tuple works :) I plan to count the number of tuples (which is 674 in this case) and put in a 'for loop' according to that count and change the start and stop time according to the tuple. Perform the loop on that single *.wav file and output on file with muted sections as the timestamps. I have no idea how to implement my thinking with FFMPEG or any other utility in Python e.g pydub. Please help me.

  



     with open('Timestamps.txt') as f:
   data = [line.split() for line in f.readlines()]
   out = [(float(k), float(v)) for k, v in data]

   r = out[0] 
   x= r[0]
   y= r[1]
   #specific x and y values
   print(x)
   print(y)