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• g++ Linking Error on Mac while compiling FFMPEG

  7 mai 2013, par Saptarshi Biswas

  g++ on Snow Leopard is throwing linking errors on the following piece of code

  test.cpp

  #include <iostream>
  
  using namespace std;
  
  #include <libavcodec></libavcodec>avcodec.h>    // required headers
  
  #include <libavformat></libavformat>avformat.h>
  
  int main(int argc, char**argv) {
  
      av_register_all();             // offending library call
  
      return 0;
  
  }
  
  </iostream>

  When I try to compile this using the following command

  g++ test.cpp -I/usr/local/include -L/usr/local/lib \
  
  -lavcodec -lavformat -lavutil -lz -lm -o test

  I get the error
  Undefined symbols :
  "av_register_all()", referenced from :
  _main in ccUD1ueX.o
  ld : symbol(s) not found
  collect2 : ld returned 1 exit status

  Interestingly, if I have an equivalent c code,
  test.c

  #include 
  
  #include <libavcodec></libavcodec>avcodec.h>
  
  #include <libavformat></libavformat>avformat.h>
  
  int main(int argc, char**argv) {
  
      av_register_all();
  
      return 0;
  
  }

  gcc compiles it just fine

  gcc test.c -I/usr/local/include -L/usr/local/lib \
  
  -lavcodec -lavformat -lavutil -lz -lm -o test

  I am using Mac OS X 10.6.5

  $ g++ --version
  
  i686-apple-darwin10-g++-4.2.1 (GCC) 4.2.1 (Apple Inc. build 5664)
  
  $ gcc --version
  
  i686-apple-darwin10-gcc-4.2.1 (GCC) 4.2.1 (Apple Inc. build 5664)

  FFMPEG's libavcodec, libavformat etc. are C libraries and I have built them on my machine like thus :

  ./configure --enable-gpl --enable-pthreads --enable-shared \
  
  --disable-doc --enable-libx264
  
  make && sudo make install

  As one would expect, libavformat indeed contains the symbol av_register_all

  $ nm /usr/local/lib/libavformat.a | grep av_register_all
  
  0000000000000000 T _av_register_all
  
  00000000000089b0 S _av_register_all.eh

  I am inclined to believe g++ and gcc have different views of the libraries on my machine. g++ is not able to pick up the right libraries. Any clue ?

• Why does my yuva444p video always lose alpha channel after transcoding to vp9 ?

  1er avril, par Ian Ye

  I'm trying to convert a video with alpha channel using FFmpeg, but the transparency information gets lost in the output.

  


  Here is the input video (prores, yuva444p) detail with ffprobe :

  


   Stream #0:1[0x2](und): Video: prores (4444) (ap4h / 0x68347061), yuva444p12le(bt709), 360x480, 73314 kb/s, 60.13 fps, 60 tbr, 600 tbn (default)
      Metadata:
        creation_time   : 2019-05-21T21:23:03.000000Z
        handler_name    : Core Media Video
        vendor_id       : appl
        encoder         : Apple ProRes 4444


  


  And my command is below :

  


  ffmpeg -i alpha_prores.mov -c:v libvpx-vp9 -pix_fmt yuva420p -auto-alt-ref 0 out.webm


  


  There is the output info :

  


  Output #0, webm, to 'out.webm':
  Metadata:
    major_brand     : qt
    minor_version   : 0
    compatible_brands: qt
    com.apple.quicktime.creationdate: 2019-05-14T13:47:17-0700
    com.apple.quicktime.location.ISO6709: +37.3367-122.0094/
    com.apple.quicktime.make: Apple
    com.apple.quicktime.model: iPhone X
    com.apple.quicktime.software: 12.1.2
    encoder         : Lavf61.7.100
  Stream #0:0(und): Video: vp9, yuva420p(tv, bt709, progressive), 360x480, q=2-31, 60 fps, 1k tbn (default)
      Metadata:
        creation_time   : 2019-05-21T21:23:03.000000Z
        handler_name    : Core Media Video
        vendor_id       : appl
        encoder         : Lavc61.19.101 libvpx-vp9
      Side data:
        cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: N/A


  


  We can see pix_fmt is still yuva420p, but after finished, I use ffprobe to check it, and the result changed !

  


    Stream #0:0: Video: vp9 (Profile 0), yuv420p(tv, bt709, progressive), 360x480, SAR 1:1 DAR 3:4, 60 fps, 60 tbr, 1k tbn (default)
      Metadata:
        alpha_mode      : 1
        HANDLER_NAME    : Core Media Video
        VENDOR_ID       : appl
        ENCODER         : Lavc61.19.101 libvpx-vp9
        DURATION        : 00:00:05.950000000


  


  The pix_fmt turn to yuv420p, which means lose alpha channel. Also we can see there is an extra info in metadata alpha_mode: 1.

  


  By the way, the result webm video can display its transparent pixel correctly in browser.

  


  When I try to overlay it on a mp4 video, transparent pixels turn to black pixels :

  


  ffmpeg -i background.mp4 -i out.webm -filter_complex "[0][1]overlay=x=10:y=10" output2.mp4


  


  And when I overlay the prores video on the same mp4, result is correct.

  


  ffmpeg -i background.mp4 -i alpha_prores.mov -filter_complex "[0][1]overlay=x=10:y=10" output2.mp4


  


  So I wonder the difference between yuva and alpha_mode:1.

  


  And the reason why vp9 would lose alpha channel when overlay on a mp4 video.

  


  It's better if you can provide other pixel format for my purpose(I want it can display correctly when overlay on mp4) !

  


  Thanks !

  


• How to create Automator service for multiple ffmpeg command

  31 janvier 2017, par user413734

  There are many tutorials for creating an automator service that calls an ffmpeg one liner script, like so e.g :

  http://apple.stackexchange.com/questions/129929/automating-ffmpeg-using-automator-service

  But I would like this service to do more than just a one liner. There is the option to chain commands with && but that makes it rather confusing.
  How can I create an automator service that does one transformation and after it is done the next line etc, e.g :

  for f in "$@"
  
  do
  
      ffmpeg -i "$f" -c:v copy -c:a copy "${f%.*}.mp4"
  
      ffmpeg -ss 00:00:01 -i "$f" -frames:v 1 "${f%.*}.jpg"
  
      ....
  
  done

  Or attach this service to one folder that if I drop a file it automatically does the require conversions.

  Thanks