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• How to capture camera devices on Windows using Libav ?

  22 septembre 2011, par Occulta

  Is there any way to capture frames from as many camera types as DirectShow do on Windows platform using Libav ? I need to capture a camera output without using DirectShow filters and I want my application to work with many camera devices types.

  I have searched the Internet about this capability of libav and found that it can be done via libav using special input format "vfwcap". Something like that (don't sure about code correctness - I wrote it by myself) :

  AVFormatParameters formatParams = NULL;
  
  AVInputFormat* pInfmt = NULL;
  
  pInFormatCtx*  pInFormatCtx = NULL;
  
  
  
  av_register_all();
  
  
  
  //formatParams.device = NULL; //this was probably deprecated and then removed
  
  formatParams.channel = 0;
  
  formatParams.standard = "ntsc"; //deprecated too but still available
  
  formatParams.width = 640;
  
  formatParams.height = 480;
  
  formatParams.time_base.num = 1000;
  
  formatParams.time_base.den = 30000; //so we want 30000/1000 = 30 frames per second
  
  formatParams.prealloced_context = 0;
  
  
  
  
  
  pInfmt = av_find_input_format("vfwcap");
  
  if( !pInfmt )
  
  {
  
    fprintf(stderr,"Unknown input format\n");
  
    return -1;
  
  }
  
  
  
  // Open video file (formatParams can be NULL for autodetecting probably)
  
  if (av_open_input_file(&pInFormatCtx, 0, pInfmt, 0, formatParams) < 0)
  
     return -1; // Couldn't open device
  
  
  
  /* Same as video4linux code*/

  So another question is : how many devices are supported by Libav ? All I have found about capture cameras output with libav on windows is advice to use DirectShow for this purpose because libav supports too few devices. Maybe situation has already changed now and it does support enough devices to use it in production applications ?

  If this isn't possible.. Well I hope my question won't be useless and this composed from different sources piece of code will help someone interested in this theme 'coz there are really too few information about it in the whole internet.

• FFmpeg trim : -to as input option vs -to as output option

  27 mai, par jackmiller

  Command 1 :

  


  > ffmpeg -ss 01:00 -to 02:00 -i "input.mp4" "output.mp4"


  


  Cuts from 01:00 to 02:00.

  


  Command 2 :

  


  > ffmpeg -ss 01:00 -i "input.mp4" -to 02:00 "output.mp4"


  


  Cuts from 01:00 to 03:00.

  


  I know, the parameter -ss as an input option, first seeks to the given position and then resets the input timestamps to 00:00. Hence, the second command cuts from 01:00 to 03:00 (in the new timestamps 00:00 to 02:00 is 01:00 to 03:00 in the original timestamps).

  


  But it's not the same in the first command. Why is that ? Is it because in the first command, the reset happens after the -to operation ?

  


• Enable 10-bit output for RGB input in AMF HEVC and AV1

  14 février, par Dmitrii Ovchinnikov

  Enable 10-bit output for RGB input in AMF HEVC and AV1
   encoders
  

  • [DH] libavcodec/amfenc.h
  • [DH] libavcodec/amfenc_av1.c
  • [DH] libavcodec/amfenc_hevc.c