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• OpenCV 3.0.0 make error with FFMPEG

  24 mars 2016, par Ujjwal Aryan

  I have been using OpenCV for a while. However I have recently changed my system to a cluster where I do not have any admin permission. The problem is like this :

  In my home folder, I installed FFMPEG (latest stable version available on ffmpeg site). I installed it in $HOME, and so in $HOME/lib there are the library files installed. For more information I compiled FFMPEG with following options :

  ./configure --prefix=$HOME --enable-shared --enable-pic

  I then downloaded the latest stable version of OpenCV 3.0.0 and configured it using ccmake. When I try to make -j8, it gives me the following error.

   Scanning dependencies of target opencv_videoio
  
  [ 63%] [ 63%] [ 63%] [ 63%] [ 63%] [ 63%] Building CXX object modules/videoio/CMakeFiles/opencv_videoio.dir/src/cap.cpp.o
  
  Building CXX object modules/videoio/CMakeFiles/opencv_videoio.dir/src/cap_mjpeg_decoder.cpp.o
  
  Building CXX object modules/videoio/CMakeFiles/opencv_videoio.dir/src/cap_images.cpp.o
  
  Building CXX object modules/videoio/CMakeFiles/opencv_videoio.dir/src/cap_v4l.cpp.o
  
  Building CXX object modules/videoio/CMakeFiles/opencv_videoio.dir/src/cap_mjpeg_encoder.cpp.o
  
  Building CXX object modules/videoio/CMakeFiles/opencv_videoio.dir/src/cap_ffmpeg.cpp.o
  
  In file included from /home/uujjwal/libraries/opencv-nogpu/opencv-3.0.0/modules/videoio/src/cap_ffmpeg.cpp:45:0:
  
  /home/uujjwal/libraries/opencv-nogpu/opencv-3.0.0/modules/videoio/src/cap_ffmpeg_impl.hpp:1546:71: error: use of enum 'AVCodecID' without previous declaration
  
  /home/uujjwal/libraries/opencv-nogpu/opencv-3.0.0/modules/videoio/src/cap_ffmpeg_impl.hpp:1556:83: error: use of enum 'AVCodecID' without previous declaration
  
  make[2]: *** [modules/videoio/CMakeFiles/opencv_videoio.dir/src/cap_ffmpeg.cpp.o] Error 1
  
  make[2]: *** Waiting for unfinished jobs....

  However without ffmpeg support it works fine. However I need ffmpeg support due to the nature of my work.

  In trying to resolve the problem, I tried installing OpenCV 2.4.11 but it also gave this error. The latest GIT version does not give me this error but rather an error a part of which goes like this

  Linking CXX shared library ../../lib/libopencv_highgui.so /usr/bin/ld: /home/matheus/ffmpeg_build/lib/../lib/libavcodec.a(avpacket.o): relocation R_X86_64_32 against `.rodata.str1.1' can not be used

  I have pasted the above error from another unresolved question online and so the folder names are different but the relocation error is exactly the same.

  In trying to resolve the problem I searched and found the following link http://answers.opencv.org/question/12597/build-problems-for-opencv-241-with-ubuntu-1204-lts/

  However, one of the answers over there mentioned changing some lines in cap_ffmpeg_impl.hpp file. I tried doing that but either i am not able to do it correctly or something else is going wrong and it is not working. Exact line numbers and exact changes are not mentioned and so I am having difficulty changing things and being sure.

  I am using Fedora 19 (Schrodinger Cat) as the operating system I hope the details of my question are clear and I hope that the community would oblige me with a good response.

  Regards
  Ujjwal

• Extracting image frames from mjpeg given 'frame byte offset' and 'frame size' [on hold]

  2 septembre 2015, par Sonia

  I’m looking for code or pointers to funtions or library that I can use to extract image frames from motion jpeg file. In my case, for each image frame, I know the starting byte offset and the size of the frame (size is not always equal for each frame). Given these data, how can I extract each image frames from mjpeg file.

  I have checked the OpenCV library, I can’t find the detail about giving these two inputs to extract frames. Also, I can’t find it in FFmpeg as well. But, I’m not an expert in these two. I hope anyone could give me pointers to this. It can be just a tool or sourcecode (I use C/C++ and MATLAB but I’m open to other language - just to learn how to do it)

  Thank you very much.

• ffmpeg concatenate with dynamic chunks

  28 octobre 2015, par vongolashu

  The ffmpeg docs for concat lists the following way
  ffmpeg -f concat -i mylist.txt -c copy output

  The mylist.txt file contains file like
  file ’/path/to/file1’
  file ’/path/to/file2’
  file ’/path/to/file3’

  What I am looking is for a way to do this concat in a persistent way where the number of files can keep increasing, for example in livestreaming
  I will be sending chunks of video (mp4 files) of 10 seconds each to my server and want to concat/stitch them together to output to a RTMP stream (for livestreaming)

  If concat is not the proper way to do this, please suggest alternatives.

  Really interested to know how people use the above concept (I hope its how it works) to send video chunks from mobile device for livestreaming