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• Link error when compiling opencv from source when including ffmpeg compiled from source

  17 septembre 2021, par Drew

  I've been stuck on this problem for weeks.

  


  I'm trying to build opencv on a raspberry pi 4 with x264 support. To do this I need to include ffmpeg, and also build that from source.

  


  However when compiling opencv, I'm consistently getting these linker errors :

  


  /usr/bin/ld: ../../lib/libopencv_videoio.so.4.5.3: undefined reference to `avcodec_get_context_defaults3'
/usr/bin/ld: ../../lib/libopencv_videoio.so.4.5.3: undefined reference to `av_lockmgr_register'
/usr/bin/ld: ../../lib/libopencv_videoio.so.4.5.3: undefined reference to `av_register_all'


  


  I'm new to Linux, so I'm not exactly sure how to get started troubleshooting this. I believe I have ffmpeg correctly compiled and installed.

  


  Here's the steps I use :

  


  Configure ffmpeg :

  


  sudo ./configure \
--prefix=/usr \
--extra-ldflags="-latomic" \
--enable-shared \
--extra-libs='-lpthread -lm' \
--ld=g++ \
--enable-gpl \
--disable-debug \
--enable-nonfree \
--enable-libx264 \
--enable-omx \
--enable-omx-rpi \
--enable-gnutls \
--enable-libfreetype \
--enable-libmp3lame


  


  Then build it :
sudo make -j4

  


  Then install it as a package : (so opencv cmake will detect it)

  


  sudo checkinstall -y --deldoc=yes --pkgversion=9999 --pkgname=ffmpeg


  


  Then configure opencv (ffmpeg is detected)

  


  sudo cmake ../opencv_sources -D CMAKE_BUILD_TYPE=RELEASE \
-D OPENCV_EXTRA_MODULES_PATH= $PWD/../opencv_contrib/modules \
-D ENABLE_NEON=ON \
-D ENABLE_VFPV3=ON \
-D BUILD_TESTS=ON \
-D INSTALL_PYTHON_EXAMPLES=OFF \
-D OPENCV_ENABLE_NONFREE=ON \
-D CMAKE_SHARED_LINKER_FLAGS='-latomic -L/usr/lib' \
-D WITH_V4L=ON \
-D WITH_QT=OFF \
-D BUILD_EXAMPLES=OFF \
-D CPU_BASELINE=NATIVE \
-D CMAKE_INSTALL_PREFIX="$HOME/opencv_build" \
-D BUILD_opencv_apps=OFF \
-D BUILD_opencv_python2=OFF \
-D BUILD_SHARED_LIBS=ON \
-D WITH_FFMPEG=ON


  


  Then build opencv :

  


  sudo make -j4


  


  And this is where I get linking errors.

  


  I checked in /usr/lib and the .so files appear to be there :

  


  ls /usr/lib | grep libav

libavcodec.a
libavcodec.so
libavcodec.so.59
libavcodec.so.59.4.101
libavdevice.a
libavdevice.so
libavdevice.so.59
libavdevice.so.59.0.100
libavfilter.a
libavfilter.so
libavfilter.so.8
libavfilter.so.8.1.103
libavformat.a
libavformat.so
libavformat.so.59
libavformat.so.59.4.101
libavutil.a
libavutil.so
libavutil.so.57
libavutil.so.57.3.100


  


  How do check where opencv is looking when linking ? And is there a way I can check the shared libraries that ffmpeg generated to make sure they work ?

  


  The ffmpeg version is : git-2021-08-10-c245963

  


  And opencv is 4.5.3-dev

  


• How can I add custom metadata to an MXF using FFMPEG ?

  15 septembre 2021, par Zak44

  I am trying to add custom metadata to an MXF in FFMPEG. I can get the syntax to go through and then my metadata to be listed during the command output, but when I later run FFMPEG on the file to check the metadata is not there. Only the material_package_name will stick. Is this not possible with MXF ?

  


  Command :

  


  ffmpeg -i Test.mp4 -vf scale=1920:1080 -an -metadata project="TEST PROJECT" -metadata comment="Test Comment" -metadata artist="Test" -metadata material_package_name="TEST VID CLIP" -b:v 36M -f mxf_opatom "TEST_VID_CLIP.mxf"


  


  Output from command :

  


      Output #0, mxf_opatom, to 'TEST_VID_CLIP.mxf':
  Metadata:
    major_brand     : mp42
    minor_version   : 0
    compatible_brands: mp42mp41
    project         : TEST PROJECT
    comment         : Test Comment
    artist          : Test
    material_package_name: TEST VID CLIP
    encoder         : Lavf58.76.100
  Stream #0:0(eng): Video: dnxhd (DNXHD), yuv422p(tv, progressive), 1920x1080 [SAR 1:1 DAR 16:9], q=2-31, 36000 kb/s, 24 fps, 24 tbn (default)
    Metadata:
      creation_time   : 2021-07-01T17:19:54.000000Z
      handler_name    : ?Mainconcept Video Media Handler
      vendor_id       : [0][0][0][0]
      encoder         : Lavc58.134.100 dnxhd


  


  Output running a check on file :

  


  ffmpeg -i TEST_VID_CLIP.mxf 
Input #0, mxf, from 'TEST_VID_CLIP.mxf':
  Metadata:
    operational_pattern_ul: 060e2b34.04010102.0d010201.10030000
    uid             : adab4424-2f25-4dc7-92ff-29bd000c0000
    generation_uid  : adab4424-2f25-4dc7-92ff-29bd000c0001
    company_name    : FFmpeg
    product_name    : OPAtom Muxer
    product_version_num: 58.76.100.0.0
    product_version : 58.76.100
    application_platform: Lavf (darwin)
    product_uid     : adab4424-2f25-4dc7-92ff-29bd000c0002
    toolkit_version_num: 58.76.100.0.0
    material_package_umid: 0x060A2B340101010501010D00136428C052947134A46428C00052947134A46400
    material_package_name: TEST VID CLIP
    timecode        : 00:00:00:00
  Duration: 00:01:05.71, start: 0.000000, bitrate: 36176 kb/s
  Stream #0:0: Video: dnxhd (DNXHD), yuv422p(tv, bt709/unknown/unknown, progressive), 1920x1080, SAR 1:1 DAR 16:9, 24 fps, 24 tbr, 24 tbn, 24 tbc
    Metadata:
      file_package_umid: 0x060A2B340101010501010D00136428C052947134A46428C00052947134A46401
At least one output file must be specified


  


• ffmpeg Grab Single Frame From Youtube Stream

  11 septembre 2021, par Rich_F

  I'm trying to grab a single frame of a streaming video on Youtube.

  


  This is an example

  


  This is the code structure I'm trying to use :

  


  ffmpeg --verbose -i $(youtube-dl -f 96 --no-playlist 'https://www.youtube.com/watch?v=XMs6LnT5mfk') -frames:1 -pred 1 clip1.jpg


  


  Trying to use youtube-dl to grab part of a stream, doesn't seem to work, and is actually throwing an ffmpeg error at me :

  


  [youtube] Q-44KECp-xQ: Downloading webpage
[youtube] Downloading just video Q-44KECp-xQ because of --no-playlist
[youtube] Q-44KECp-xQ: Downloading m3u8 information
[youtube] Q-44KECp-xQ: Downloading MPD manifest
[download] Destination: Ryde Esplanade & Pier, Isle of Wight UK _ Railcam LIVE 2021-09-11 03_25-Q-44KECp-xQ.mp4

ERROR: ffmpeg exited with code -9


  


  How can I achieve this ? I'm open to reworking this approach, or moving to something completely different. Cheers