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• How to write v4l2 application with vivid (virtual video driver) for capturing video ?

  8 janvier 2016, par ransh

  I am trying to understand how to write v4l2 application.
  There is very well example in http://linuxtv.org/downloads/v4l-dvb-apis/capture-example.html , so I wanted to try to use it for capturing video with vivid (virtual device driver).

  I tried several resolution, pixelformat, different inputs,
  but on trying to display the captured file, it always has a sync problems ( the test bars of the video are keep moving in the horizontal axis).
  I tried to change resolution, pixelformat, in both capture application or player , but nothing helps.

  I compiled the v4l2 API example AS-IS from :
  http://linuxtv.org/downloads/v4l-dvb-apis/capture-example.html
  with minor modification in the —force part of the example (I also tried the example as is without modifications but it did not help), so that I choose hd input , and 1920x1080 resolution, V4L2_PIX_FMT_YUV420 (also tried V4L2_PIX_FMT_YUV422P) , progressive.

    if (force_format) {
  
              input = 3;  // <<-- HD input device
  
              if (-1==xioctl(fd,VIDIOC_S_INPUT,&input))
  
              {
  
               errno_exit("VIDIOC_S_INPUT");
  
              }
  
              fmt.fmt.pix.width       = 1920;
  
              fmt.fmt.pix.height      = 1080;
  
              fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_YUV420; // <<- tried also V4L2_PIX_FMT_YUV422P
  
              fmt.fmt.pix.field       = V4L2_FIELD_NONE; // <- trying to capture progressive
  
  
  
              if (-1 == xioctl(fd, VIDIOC_S_FMT, &fmt))
  
                      errno_exit("VIDIOC_S_FMT");
  
  
  
      } else {

  I run the application with (the compiled code using pixelformat = V4L2_PIX_FMT_YUV420 trial ) :

  ./v4l2_example -f -o -c 10  > cap_yuv420p.yuv 

  And (the compiled code using pixelformat = V4L2_PIX_FMT_YUV422P trial )

  ./v4l2_example -f -o -c 10  > cap_yuv422p.yuv 

  I’ve tried to play them with :

  ffplay -f rawvideo -pixel_format yuv420p -video_size 1920x1080 -i cap_yuv420p.yuv 

  And

  ffplay -f rawvideo -pixel_format yuv422p -video_size 1920x1080 -i cap_yuv422p.yuv 

  These are the captured video files from my above trials :

  https://drive.google.com/folderview?id=0B22GsWueReZTUS1tSHBraTAyZ00&usp=sharing

  I probably am doing something wrong.
  Is there any idea what’s wrong in my configurations or how I can debug it better ?

• Running list of cmd.exe commands from maya in Python

  17 décembre 2015, par user3541686

  I am writing a maya python script to batch render a scene into jpgs then use ffmpeg to turn them into a mov. Currently the script saves a string of commands as a bat file which works fine but I’d prefer to just run cmd.exe from maya and execute the list of commands without creating that bat first.

  I’ve been reading about "subprocess.popen()" but I can’t figure out how to get it to iterate through each line, run that command, then move onto the next one when done ie :

  1) Run maya render.exe & save scene as jpegs

  2) ffmpeg jpgs to mov

  I’ve shortened the directories but its essentially this :

  `C:\PROGRA~1\Autodesk\Maya2015\bin\Render.exe -r hw2 -s 100 -e 200 -of jpg -fnc 7 -x 1920 -y 1080 -rd 
  
  "C:\RENDER" 
  
  "C:\SCENE.ma" ffmpeg -y -r 25 -start_number 0100 -i C:\SCENE_%%04d.jpg C:\SCENE.mov

  How would I be able to do this ?

  Thanks !

• Proportion for the values of maxrate, mnrate and bufsize for encoding videos for streaming purpose and past duration too large warning

  15 décembre 2015, par himanshu nautiyal

  can you please tell me about minrate, maxrate and bufsize. And is it necessary to give maxrate and minrate for encoding videos for streaming purpose. Actually I understood the meaning and functions of minrate, maxrate and bufsize through ffmpeg documents but I am not finding any solution of what would be difference in between the values of these three.

  for example : I am using this command
  ffmpeg -y -i testing.mp4 -c:a libfdk_aac -ac 2 -ab 128k -c:v libx264 -r 24 -g 24 -b:v 2m -maxrate 1m -bufsize 1m -vf scale=1920*1080 aa.mp4

  but I am not sure if this -b:v 2m -maxrate 1m bufsize 1m is in correct propotions or not. My output is fine but I don’t want any problem on working real time. Moreover, I am also getting the following warning

  Past duration 0.634361 too large
  Past duration 0.674370 too large
  Past duration 0.714363 too large 0kB time=00:00:01.32 bitrate= 0.3kbits/s

  Past duration 0.754372 too large
  Past duration 0.794365 too large
  Past duration 0.834373 too large
  Past duration 0.874367 too large
  Past duration 0.914360 too large
  Past duration 0.954369 too large

  thanks in advance