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• Implement sws_scale() with opencv

  21 mai 2017, par Aviv Sharon

  I need to convert an AVFrame (ffmpeg) to cv::Mat (or IplImage), from a yuv420 plain representation with AVFrame (3 data buffers, 1 for Y, 1 for U(size of Y/2), and 1 for V(size of Y/2)) to BGR24.
  This is possible using ffmpeg’s sws_scale() function, and it works fine.
  Now, I need to implement it using openCV (2.4.6), but I can’t find such answers on the web, how to merge 3 channels/Mats (YUV), different in size (420 representation), to a BGR24 (color formatting) Mat.
  Would love to get your kind help here.

  thanks !

• How to configure FFMPEG to generate position independent code on IOS

  8 juillet 2013, par madadi

  I am developing an app on iOS which makes use of FFMPEG for video decoding. I want to get 'position independent code' of FFMPEG working on my app. --enable-pic option in the FFMPEG configuration generates position independent code only if I set --disable-asm. I concluded this when I ran the otool on my app(otool -hv 'appname'). Below are the details :

  If I set --enable-pic alone, below is the output with otool :

  magic     cputype  cpusubtype  caps  filetype  ncmds  sizeofcmds  flags
  
  MH_MAGIC  ARM      V7          0x00  EXECUTE   29     3724        NOUNDEFS DYLDLINK TWOLEVEL WEAK_DEFINES BINDS_TO_WEAK

  If I set --enable-pic and --disable-asm below is the output with otool,

  magic     cputype  cpusubtype  caps  filetype  ncmds  sizeofcmds  flags
  
  MH_MAGIC  ARM      V7          0x00  EXECUTE   51     5520        NOUNDEFS DYLDLINK TWOLEVEL WEAK_DEFINES BINDS_TO_WEAK **PIE** 

  Below are my configuration settings for FFMPEG(build-ffmpeg-ios.sh) :

  if [  `uname` =  "Darwin" ]; then
  
    SEDCMD="sed -i '' "
  
  else
  
    SEDCMD="sed -i "
  
  fi
  
  
  
  
  
  make clean
  
  ./configure \
  
      --prefix=$PREFIX \
  
      --enable-version3 \
  
      --enable-static \
  
      --disable-shared \
  
      --disable-doc \
  
      --disable-ffmpeg \
  
      --disable-ffplay \
  
      --disable-ffprobe \
  
      --disable-ffserver \
  
      --disable-avdevice \
  
      --disable-avfilter \
  
      --disable-postproc \
  
      --enable-small \
  
      --cross-prefix="$DEVROOT/usr/bin/" \
  
      --enable-cross-compile \
  
      --target-os=darwin \
  
      --arch=$ARCH \
  
      --cpu=$CPU \
  
      --cc="$CC" \
  
      --as="$AS" \
  
      --extra-cflags="$CFLAGS" \
  
      --extra-ldflags="$CFLAGS" \
  
      --disable-symver \
  
      --disable-debug \
  
      --disable-indevs \
  
      --disable-encoders \
  
      --disable-bsfs \
  
      --enable-pic \
  
      --disable-filters \
  
      $CONFIGURE_FLAGS || exit 1;
  
  $SEDCMD 's/HAVE_INLINE_ASM 1/HAVE_INLINE_ASM 0/g' config.h
  
  make install || exit 1;

  And below is the make file I use(iOS.mk) :

  FFMPEG_LIBS := libavcodec.a libavformat.a libavutil.a libswscale.a
  
  
  
  IOS_ARMV7_FFMPEG_LIB := $(addprefix build/ios/armv7/lib/, $(FFMPEG_LIBS))
  
  
  
  IOS_UNI_FFMPEG_LIB := $(addprefix build/ios/universal/lib/, $(FFMPEG_LIBS))
  
  
  
  
  
  
  
  IPHONE_SDK_VERSION := "5.0"
  
  IPHONE_DEPLOY_SDK := "3.2"
  
  
  
  ALL_IOS_LIBS := $(IOS_UNI_FFMPEG_LIB) 
  
  
  
  build/ios/universal/lib/%.a : build/ios/armv7/lib/%.a
  
      mkdir -p build/ios/universal/lib
  
      lipo -create -output $@ $^
  
  
  
  
  
  
  
  $(IOS_ARMV7_FFMPEG_LIB): 
  
      export PREFIX="`$(ABSPATH) build/ios/armv7`" && \
  
      export ARCH="arm" && \
  
      export CPU="cortex-a8" && \
  
      export IOS_BASE_SDK="$(IPHONE_SDK_VERSION)" && \
  
      export IOS_DEPLOY_TGT="$(IPHONE_DEPLOY_SDK)" && \
  
      export CONFIGURE_FLAGS="--enable-neon" && \
  
      export PATH="`$(ABSPATH) venders`:$$PATH" && \
  
      cd venders/ffmpeg && bash ../iphone-compile.sh arm7 ../build-ffmpeg-ios.sh

  Can someone please help me with getting the FFMPEG up and running with both 'pic' and assembly optimization enabled. Without assembly optimizastion, FFMPEG would not be helpful to me as the video decoding is extremely slow.

• Error with os.system in python script

  25 mai 2015, par Avery Ripoll Crocker

  I am creating a python script that will convert files using ffmpeg and unoconv. However when I run the program, rather than getting a converted file the program simply displays the text :

  sh: 1: unoconv -f: not found

  Here is the script for my program :

      path = raw_input("Please drag and drop the directory in which the file is stored into the terminal:")
  
      os.chdir(path[1:-2])
  
      filename = raw_input("Please enter the name of the file you would like to convert, including the file-type. e.g. test.txt, however please do make sure that the file-name does not have any spaces:")
  
      Fileextension = raw_input("What filetype would you like the program to convert your file to. E.g. .mp3: ")
  
      body, ext = os.path.splitext("filename")
  
      os.system("'ffmpeg -i ' + filename + body + Fileextension ")

  Any ideas as to why this happens ?