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• Unable to link against FFmpeg libaries

  2 mars 2023, par Cody

  I tried to build this, but always got link-time error.

  



  #include <libavutil></libavutil>log.h>    &#xA;int main(int argc, char *argv[])&#xA;{&#xA;    ::av_log_set_flags(AV_LOG_SKIP_REPEATED);&#xA;    return 0;&#xA;}&#xA;

  



  My distro is Debian GNU/Linux 8 (jessie). The FFmpeg was built by myself, and the configure command was...

  



  $ ./configure --prefix=/usr/local --disable-static --enable-shared \
> --extra-ldflags='-Wl,-rpath=/usr/local/lib'


  



  The link-error is as follows.

  



  $ g++ foo.cpp -D__STDC_CONSTANT_MACROS -Wall \
> -Wl,-rpath=/usr/local/lib \
> $(pkg-config --cflags --libs libavutil)
/tmp/ccKzgEFb.o: In function `main':
foo.cpp:(.text+0x17): undefined reference to `av_log_set_flags(int)'
collect2: error: ld returned 1 exit status


  



  where the output of pkg-config is...

  



  $ pkg-config --cflags --libs libavutil
-I/usr/local/include -L/usr/local/lib -lavutil


  



  The objdump shows that the shared object libavutil.so does have av_log_set_flogs inside.

  



  $ objdump --dynamic-syms /usr/local/lib/libavutil.so | grep 'av_log_set_flags'
000260f0 g    DF .text  0000000a  LIBAVUTIL_54 av_log_set_flags


  



  Please note that the g++ command used to build the above application had a linker option -Wl,-rpath=/usr/local/lib, though it still doesn't work. Also, I've tried to monitor with inotifywait if the other version provided by the distro were called. They were not, and the one being opened during execution of g++ was /usr/local/lib/libavutil.so.

  



  Summary :

  



  


  1. /usr/local/lib/libavutil.so does have the symbol.

  


  2. -rpath was used to force to link against the shared library.

  


  3. Why link-time error ? T_T

  


  



  Any suggestion or information would be highly appreciated ! Thanks !

  



  REEDIT : ffplay works fine and ldd shows it use /usr/local/lib/libavutil.so. So, the libraries seems not broken, and the problem becomes how to build my own codes to use the libraries.

  


• Unable to link against FFmpeg libaries

  28 octobre 2015, par Cody

  I tried to build this, but always got link-time error.

  #include <libavutil></libavutil>log.h>    
  
  int main(int argc, char *argv[])
  
  {
  
      ::av_log_set_flags(AV_LOG_SKIP_REPEATED);
  
      return 0;
  
  }

  My distro is Debian GNU/Linux 8 (jessie). The FFmpeg was built by myself, and the configure command was...

  $ ./configure --prefix=/usr/local --disable-static --enable-shared \
  
  > --extra-ldflags='-Wl,-rpath=/usr/local/lib'

  The link-error is as follows.

  $ g++ foo.cpp -D__STDC_CONSTANT_MACROS -Wall \
  
  > -Wl,-rpath=/usr/local/lib \
  
  > $(pkg-config --cflags --libs libavutil)
  
  /tmp/ccKzgEFb.o: In function `main':
  
  foo.cpp:(.text+0x17): undefined reference to `av_log_set_flags(int)'
  
  collect2: error: ld returned 1 exit status

  where the output of pkg-config is...

  $ pkg-config --cflags --libs libavutil
  
  -I/usr/local/include -L/usr/local/lib -lavutil

  The objdump shows that the shared object libavutil.so does have av_log_set_flogs inside.

  $ objdump --dynamic-syms /usr/local/lib/libavutil.so | grep 'av_log_set_flags'
  
  000260f0 g    DF .text  0000000a  LIBAVUTIL_54 av_log_set_flags

  Please note that the g++ command used to build the above application had a linker option -Wl,-rpath=/usr/local/lib, though it still doesn’t work. Also, I’ve tried to monitor with inotifywait if the other version provided by the distro were called. They were not, and the one being opened during execution of g++ was /usr/local/lib/libavutil.so.

  Summary :

  1. /usr/local/lib/libavutil.so does have the symbol.

  2. -rpath was used to force to link against the shared library.

  3. Why link-time error ? T_T

  Any suggestion or information would be highly appreciated ! Thanks !

  REEDIT : ffplay works fine and ldd shows it use /usr/local/lib/libavutil.so. So, the libraries seems not broken, and the problem becomes how to build my own codes to use the libraries.

• How to work with data received from streaming services in my Java application ?

  24 novembre 2020, par gabriel garcia

  I'm currently trying to develop an "streaming client" as a way to organize multiple stream services (twitch, yt, mitele...) in a single desktop application written in Java.

  


  It basically relies on streamlink (which relies in ffmpeg) thanks to all it's features so my project could be defined as a frontend for streamlink.

  


  Straight to the point, one of the features I'd like to add it is the option to programatically record streams in the background and showing this video stream to the user when it's requested. Since there's also the possibility that the user wants to watch the stream without recording it, I'm forced to work with all that byte-like data sent from those streaming sources.

  


  So, the problem is basically that I do not know much about video coding/decoding/muxing/demuxing nor video theory like container structure, video formats and such.

  


  But the idea is to work with all the data sent from the stream source (let's say twitch, for example), read this bytes (I'm not sure what kind of information is sent to the client nor format) from the java.lang.Process's stdout and then present it to the client.

  


  Here's another problem : I don't know how to play video streams in JavaFX and I don't think it's even supported right now. So I would have to extract each frame and sound associated from the stdout and show them to the user each time a new frame is received (oups, another problem since I don't know when does each frame starts/ends since I'm reading each stdout's line).

  


  As a summary :

  


  

  • What kind of data am I receiving from the streaming source ?

  


  • How can I know when does each frame starts/stops ?

  


  • How can I extract the image and sound from each frame ?

  


  


  I hope I'm not asking too much and that you could shed some light upon my darkness.