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• OpenCv and ffmpeg working toghether on iOS

  1er avril 2014, par jjca

  I'm developing an iOS app which captures frames from camera with openCV, following this tutorial, and encodes those frames into a video using ffmpeg.

  The capture works fine, the problem comes with the ffmpeg part. I'm getting the following linker error when i try to use anything of ffmpeg :

  Undefined symbols for architecture armv7 :
  "avcodec_find_encoder(AVCodecID)", referenced from :
  -[ViewController processImage :] in ViewController.o
  ld : symbol(s) not found for architecture armv7
  clang : error : linker command failed with exit code 1 (use -v to see invocation)

  It only happens when the class file is named *.mm but not using ffmpeg in pure objective-c code.

  I'm using the binaries provided by openCV and compiling the ffmpeg ones by myself.

  Would compile them together fix the problem ? is possible to this ?

• ffmpeg not working with filenames that have whitespace

  1er avril 2017, par cmw

  I’m using FFMPEG to measure the duration of videos stored in an Amazon S3 Bucket.

  I’ve read the FFMPEG docs, and they explicitly state that all whitespace and special characters need to be escaped, in order for FFMPEG to handle them properly :

  See docs 2.1 and 2.1.1 : https://ffmpeg.org/ffmpeg-utils.html

  However, when dealing with files whose filenames contain whitespace, ffmpeg fails to render a result.

  I’ve tried the following, with no success

  ffmpeg -i "http://s3.mybucketname.com/videos/my\ video\ file.mov" 2>&1 | grep Duration | awk '{print $2}' | tr -d
  
  ffmpeg -i "http://s3.mybucketname.com/videos/my video file.mov" 2>&1 | grep Duration | awk '{print $2}' | tr -d
  
  ffmpeg -i "http://s3.mybucketname.com/videos/my'\' video'\' file.mov" 2>&1 | grep Duration | awk '{print $2}' | tr -d
  
  ffmpeg -i "http://s3.mybucketname.com/videos/my\ video\ file.mov" 2>&1 | grep Duration | awk '{print $2}' | tr -d

  However, if I strip out the whitespace in the filename – all is well, and the duration of the video is returned.

  Any help is appreciated !

• OpenCV no longer working after Homebrew install

  28 mars 2014, par Tom smith

  I have have been running OpenCV from QT creator on Mac OSX.
  I was having trouble getting VideoWriter to work so it was suggested I try installing ffmpeg with opencv.
  Using brew I executed this command

  brew install homebrew/science/opencv --with-ffmpeg 

  However, during this process I received the following error

  Warning: Could not link opencv. Unlinking...
  
  Error: The `brew link` step did not complete successfully
  
  The formula built, but is not symlinked into /usr/local
  
  You can try again using `brew link opencv'

  The "possible conflicting files were mostly from "/usr/local/include/opencv2/"

  I tried the command brew suggested but this gave me a permission denied warning so I found a fix to execute before the command, both of which are below.

  sudo chown -R `whoami` /usr/local
  
  brew link --overwrite opencv

  This appeared to execute correctly giving me the following response

  Linking /usr/local/Cellar/opencv/2.4.8.2... 251 symlinks created

  The problem is this now seems to have broken my working project. When I try to run the project now I get the following errors
  Unfortunately after trying to rebuild the project I cannot get the error below to show up in the terminal again but it said the following error, was expected in /usr/local/include but not found in the build directory (afraid I cannot be sure of the exact wording)

  dyld: lazy symbol binding failed:

  In QT creator however, when trying to build the project it says

  error: symbol(s) not found for architecture x86_64
  
  error: linker command failed with exit code 1 (use -v to see invocation)

  Any suggestions for a fix, and also how I can get VideoWriter to work with opencv on Mac OSX after I have my project working again ?