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• opencv installation ffmpeg error

  22 avril 2016, par tGeek

  I have been trying to install opencv for a long time in my fedora 20 32 bit system.I followed the instructions from http://docs.opencv.org/trunk/doc/py_tutorials/py_setup/py_setup_in_fedora/py_setup_in_fedora.html#install-opencv-python-in-fedora
  But after all cmake commands when I m trying to make it I am getting an error again and again.

      scanning dependencies of target opencv_createsamples
  
       [100%] Building CXX object    apps/haartraining/CMakeFiles/opencv_createsamples.dir/createsamples.cpp.o
  
      Linking CXX executable ../../bin/opencv_createsamples
  
     /lib/libavcodec.so.55: undefined reference to `vpx_codec_vp9_dx_algo'
  
      /lib/libavcodec.so.55: undefined reference to `vpx_codec_vp9_cx_algo'
  
      collect2: error: ld returned 1 exit status
  
      make[2]: *** [bin/opencv_createsamples] Error 1
  
     make[1]: *** [apps/haartraining/CMakeFiles/opencv_createsamples.dir/all] Error 2
  
      make: *** [all] Error 2

  I have followed so many articles about the ffmpeg versions and updating stuff but did understand a little. but when I tried

  $ sudo yum update ffmpeg

  I got the error as

  >Package(s) ffmpeg available, but not installed.
  
  No packages marked for update

  What should I do ?

• Finding duration/number of frames of WebM using FFMPEG/libavformat

  12 septembre 2015, par gcgrant

  I’m trying to retrieve the duration and number of frames from a WebM file using FFMPEG and libavformat. I’m adapting some code that was initially written to work with MP4s, and when passing an MP4 it seems to work fine.

  I have FFMPEG 2.1 compiled with the vp8 parser and decoder and the matroska demuxer.

  I have an AVStream pointer to the video stream, *video_st. The code looks for the number of frames in video_st->nb_frames, and for the duration in video_st->duration. These both appear to be 0.

  The API docs for for video_st->duration (https://ffmpeg.org/doxygen/trunk/structAVStream.html#a4e04af7a5a4d8298649850df798dd0b) say that "If a source file does not specify a duration, but does specify a bitrate, this value will be estimated from bitrate and file size." I can confirm that that this file does specify a duration and a bitrate (as I tested it on my desktop with ffmpeg -i). So it seems odd that this is returning 0. Perhaps my FFMPEG build configuration is incorrect ?

  As for nb_frames, the docs say "number of frames in this stream if known or 0". Is there anything I can do if this returns 0 ? Again, ffmpeg -i does return an estimate for fps ; that would be good enough, as I could estimate the number of frames with that and the duration.

  Thanks !

• mp4 video fragmented using ffmpeg takes long time to start playing

  14 mai 2020, par daldoy

  When using ffmpeg, to stream the output file to S3, it is required to use "-movflags frag_keyframe", and the generated file will be a fragmented mp4.

  



  When I try to play this files from S3 it takes a long time to start playing. I have tried the recommended movflags from MDN Docs and all the possible combinations.

  



  ffmpeg -i https://notreal-bucket.s3-us-west-1.amazonaws.com/video/video.mp4 -f mp4 -movflags frag_keyframe+empty_moov pipe:1 | aws s3 cp - s3://notreal-bucket/video/output.mp4

  



  Link of the file : https://happy-testing.s3-eu-west-1.amazonaws.com/stack-overflow/help.mp4