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• Creating periodic offsets with ffmpeg segment muxer for seamless ffmpeg-concat transitions

  30 janvier 2021, par Soren Wray

  Suppose I begin with a 1 minute video with a framerate output of 24 frames/second and then use ffmpeg's segment muxer to split it into 60 equal parts of 1 second each with the timesptamps reset :

  


  ffmpeg -i input.mp4 -map 0 -f segment -segment_time 1 -reset_timestamps 1 -g 24 output_%03d.mp4

  


  I then use ffmpeg-concat to string output_000.mp4-output_059.mp4 together into a single video with a periodic 0.5 second dreamy transition effect between each segment : ffmpeg-concat -t dreamy -d 500 -o dreamy.mp4 output_*.mp4

  


  Unfortunately, the transition effects introduce a negative 0.5 second offset between the segments, resulting in a video that is 32 seconds in duration. I don't want to deform the audio and video in this manner. I want to use transition effects without changing the duration or creating any other syncing issues. How to best achieve these seamless transitions is the question.

  


  One potential solution would be to add an offset to the segments, e.g. 0.25 seconds at the beginning and end of every segment, such that the segment muxer produces 60 segments of 1.5 second duration from a 1 minute video. In this manner, the 0.5 second transition effects should blend seamlessly into the offsets.

  


  I don't know where to begin to achieve this potential solution. I've read the official guide, but I can't decipher the relevant filter options for this particular use case. ffmpeg-concat doesn't seem to provide any native options around this problem either.

  


• Compiling FFMPEG with libvpx on Mac OS X

  26 août 2014, par Dalvik

  I’m having hard timed trying to manually compile FFMPEG on my MAC. I’m trying to compile it with —enable-libvpx but keep getting this annoying error :

  ERROR: libvpx decoder version must be >=0.9.1"

  I’m compiling FFMPEG using this guide by ROMAN10 and this link from the FFMPEG official documentation. You can find the build script I’m using in ROMAN’s web page.

  Note : I’m working with HomeBrew because I found it easier and more convenient tool from which I can install all the core packages that ffmpeg requires(yasm,libogg,libvorbis and more).

  In an efforts to solve it I’ve try to fix ffmpeg’s ./configure file and notice that the link to libvpx is as follow :

  enabled libvpx            && {
  
  enabled libvpx_vp8_decoder && { check_lib2 "vpx/vpx_decoder.h vpx/vp8dx.h" vpx_codec_dec_init_ver -lvpx ||
  
                                  die "ERROR: libvpx decoder version must be >=0.9.1"; }
  
  enabled libvpx_vp8_encoder && { check_lib2 "vpx/vpx_encoder.h vpx/vp8cx.h" "vpx_codec_enc_init_ver VP8E_SET_MAX_INTRA_BITRATE_PCT" -lvpx ||
  
                                  die "ERROR: libvpx encoder version must be >=0.9.7"; }
  
  enabled libvpx_vp9_decoder && { check_lib2 "vpx/vpx_decoder.h vpx/vp8dx.h" "vpx_codec_vp9_dx" -lvpx || disable libvpx_vp9_decoder; }
  
  enabled libvpx_vp9_encoder && { check_lib2 "vpx/vpx_encoder.h vpx/vp8cx.h" "vpx_codec_vp9_cx VP9E_SET_AQ_MODE" -lvpx || disable libvpx_vp9_encoder; } }

  You can see that the method check_lib2 receives 2 params - the header path and the function’s name. Unfortunately even when I’m changing the path to a downloaded version of libvpx(which is much newer than 0.9.1) I’m still getting this error. Any help would be much appreciated.

• opencv3.1 python VideoCapture black screen

  3 mai 2017, par alex

  i’m trying to use opencv3.1 with python3.5
  following this official)tutorial
  http://docs.opencv.org/3.0-beta/doc/py_tutorials/py_gui/py_video_display/py_video_display.html#display-video

  the camera led is "on" but the window doesn’t show any image (black)

  my current enviroment :
   windows 10
   python 3.5.2 (32bit)
   numpy 1.12.0b1 (32bit) binaries downloaded from : http://www.lfd.uci.edu/ gohlke/pythonlibs/
   opencv 3.1.0 (32bit) binaries downloaded from : http://www.lfd.uci.edu/ gohlke/pythonlibs/

  they seem installed correctly !

  as the tutorial says :

  Note Make sure proper versions of ffmpeg or gstreamer is installed. Sometimes, it is a headache to work with Video Capture mostly due to wrong installation of ffmpeg/gstreamer.

  i’ve no ffmpeg installed !!! so i suppose this is the cause of my problem
  so the questions are :
  1) which version of ffmpeg is needed ?
  2) how install ffmpeg on windows ? it seems a setup doesn’t exist(there is a binary section with a zip file ? how to use it after unzipped ?)
  3) is possible to see(in some way) if the opencv binaries(that i’ve downloaded) were compiled with ffmpeg support(flag ?)

  PS : i’ve tried to add the ffmpeg folder path the the PATH enviroment variable but nothing change