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• ffmpeg on iOS 5.1 Undefined Symbols Error

  25 avril 2012, par AndyDunn

  So I've spent several hours now working through the scant amount of information available online about building ffmpeg for iOS. The building process seems to work well and I end up with fat files for armv6 and armv7 which I drag over into my project.

  However, whenever I try to use the "avcodec_init()" command I get the following error :

  Undefined symbols for architecture armv7 :
  "_avcodec_init", referenced from :

   -[FirstViewController viewDidLoad] in FirstViewController.o

  ld : symbol(s) not found for architecture armv7

  clang : error : linker command failed with exit code 1 (use -v to see invocation)

  The library files are included in the 'Link Binary with Libraries' of the project settings, so they are definitely compiled into the app. I just can't for the life of me work out why I'm getting an error on this.

  I've tried several different projects, and downloaded some existing project files from the web and get the same error.

  This is the build script I used :

  export PLATFORM="iPhoneOS" export MIN_VERSION="4.0" export
  MAX_VERSION="5.1" export
  DEVROOT=/Volumes/Lion/Applications/Xcode.app/Contents/Developer/Platforms/$PLATFORM.platform/Developer
  export SDKROOT=$DEVROOT/SDKs/$PLATFORM$MAX_VERSION.sdk export
  CC=$DEVROOT/usr/bin/llvm-gcc export LD=$DEVROOT/usr/bin/ld export
  CPP=$DEVROOT/usr/bin/cpp export CXX=$DEVROOT/usr/bin/llvm-g++ export
  AR=$DEVROOT/usr/bin/ar export LIBTOOL=$DEVROOT/usr/bin/libtool export
  NM=$DEVROOT/usr/bin/nm export CXXCPP=$DEVROOT/usr/bin/cpp export
  RANLIB=$DEVROOT/usr/bin/ranlib

  COMMONFLAGS="-pipe -gdwarf-2 -no-cpp-precomp -isysroot $SDKROOT
  -marm -fPIC" export LDFLAGS="$COMMONFLAGS -fPIC" export CFLAGS="$COMMONFLAGS -fvisibility=hidden" export
  CXXFLAGS="$COMMONFLAGS -fvisibility=hidden
  -fvisibility-inlines-hidden"

  FFMPEG_LIBS="libavcodec libavdevice libavformat libavutil libswscale"

  echo "Building armv6..."

  make clean ./configure \
  —cpu=arm1176jzf-s \
  —extra-cflags='-arch armv6 -miphoneos-version-min=$MIN_VERSION -mthumb' \
  —extra-ldflags='-arch armv6 -miphoneos-version-min=$MIN_VERSION' \
  —enable-cross-compile \
  —arch=arm \
  —target-os=darwin \
  —cc=$CC \
  —sysroot=$SDKROOT \
  —prefix=installed \
  —disable-network \
  —disable-decoders \
  —disable-muxers \
  —disable-demuxers \
  —disable-devices \
  —disable-parsers \
  —disable-encoders \
  —disable-protocols \
  —disable-filters \
  —disable-bsfs \
  —enable-decoder=h264 \
  —enable-decoder=svq3 \
  —enable-gpl \
  —enable-pic \
  —disable-doc perl -pi -e 's/HAVE_INLINE_ASM 1/HAVE_INLINE_ASM 0/' config.h make -j3

  mkdir -p build.armv6 for i in $FFMPEG_LIBS ; do cp ./$i/$i.a
  ./build.armv6/ ; done

  echo "Building armv7..."

  make clean ./configure \
  —cpu=cortex-a8 \
  —extra-cflags='-arch armv7 -miphoneos-version-min=$MIN_VERSION -mthumb' \
  —extra-ldflags='-arch armv7 -miphoneos-version-min=$MIN_VERSION' \
  —enable-cross-compile \
  —arch=arm \
  —target-os=darwin \
  —cc=$CC \
  —sysroot=$SDKROOT \
  —prefix=installed \
  —disable-network \
  —disable-decoders \
  —disable-muxers \
  —disable-demuxers \
  —disable-devices \
  —disable-parsers \
  —disable-encoders \
  —disable-protocols \
  —disable-filters \
  —disable-bsfs \
  —enable-decoder=h264 \
  —enable-decoder=svq3 \
  —enable-gpl \
  —enable-pic \
  —disable-doc perl -pi -e 's/HAVE_INLINE_ASM 1/HAVE_INLINE_ASM 0/' config.h make -j3

  mkdir -p build.armv7 for i in $FFMPEG_LIBS ; do cp ./$i/$i.a
  ./build.armv7/ ; done

  mkdir -p build.universal for i in $FFMPEG_LIBS ; do lipo -create
  ./build.armv7/$i.a ./build.armv6/$i.a -output ./build.universal/$i.a ;
  done

  for i in $FFMPEG_LIBS ; do cp ./build.universal/$i.a ./$i/$i.a ; done

  make install

• Add mp3 file sound in the middle of the mp4/avi/mpeg [on hold]

  17 novembre 2014, par user1018697

  I tryed to do something, and i meet some diffulties to do :

  1- i have a little movie file of 1 minutes ( movie.mp4)

  2- i have an mp3 file of 10 seconds (voice.mp3)

  I whish to add this mp3 file in the middle of my film (at 30 seconds).
  My question is :
  Is it possible create simply a new video (movie2.mp4) with my mp3 added in the middle of the film (at 30 s) ?
  Or maybe is exist a c# library or c++ to do this ?

  Thanks

• How To Write An Oscilloscope

  29 avril 2012, par Multimedia Mike — General, gme, oscilloscope, visualization

  I’m trying to figure out how to write a software oscilloscope audio visualization. It’s made more frustrating by the knowledge that I am certain that I have accomplished this task before.

  In this context, the oscilloscope is used to draw the time-domain samples of an audio wave form. I have written such a plugin as part of the xine project. However, for that project, I didn’t have to write the full playback pipeline— my plugin was just handed some PCM data and drew some graphical data in response. Now I’m trying to write the entire engine in a standalone program and I’m wondering how to get it just right.

  
  
  

  This is an SDL-based oscilloscope visualizer and audio player for Game Music Emu library. My approach is to have an audio buffer that holds a second of audio (44100 stereo 16-bit samples). The player updates the visualization at 30 frames per second. The o-scope is 512 pixels wide. So, at every 1/30th second interval, the player dips into the audio buffer at position ((frame_number % 30) * 44100 / 30) and takes the first 512 stereo frames for plotting on the graph.

  It seems to be working okay, I guess. The only problem is that the A/V sync seems to be slightly misaligned. I am just wondering if this is the correct approach. Perhaps the player should be performing some slightly more complicated calculation over those (44100/30) audio frames during each update in order to obtain a more accurate graph ? I described my process to an electrical engineer friend of mine and he insisted that I needed to apply something called hysteresis to the output or I would never get accurate A/V sync in this scenario.

  Further, I know that some schools of thought on these matters require that the dots in those graphs be connected, that the scattered points simply won’t do. I guess it’s a stylistic choice.

  Still, I think I have a reasonable, workable approach here. I might just be starting the visualization 1/30th of a second too late.