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• Linking ffmpeg's libswresample from MacOS X 10.9 with C++

  8 janvier 2014, par user2530102

  I am trying to link to ffmpeg's libswresample from a C++ application. I have installed ffmpeg through Homebrew on Mac OS X 10.9. A simple test application links if it's compiled as C, but not if it's compiled as C++. Here is the sample code :

  #include 
  
  #include <libswresample></libswresample>swresample.h>
  
  
  
  int main()
  
  {
  
    swr_alloc();
  
    printf("Hello world\n");
  
    return 0;
  
  }

  When compiled as C with clang -I/usr/local/include -L/usr/local/lib -lswresample -o hello hello.c this creates the application as expected. When compiled with C++ using clang++ -I/usr/local/include -L/usr/local/lib -lswresample -o hello hello.cc it results in an error like the following :

  Undefined symbols for architecture x86_64:
  
    "swr_alloc()", referenced from:
  
        _main in hello-9jqOY4.o
  
  ld: symbol(s) not found for architecture x86_64
  
  clang: error: linker command failed with exit code 1 (use -v to see invocation)

  But running nm -a /usr/local/lib/libswresample.dylib includes 000000000000d8a9 T _swr_alloc and file /usr/local/lib/libswresample.dylib shows /usr/local/lib/libswresample.dylib: Mach-O 64-bit dynamically linked shared library x86_64 which I assume is expected. I have the same issue compiling the example with gcc/g++, and I also have the same issue when compiling ffmpeg with either clang or gcc, which leads me to think that there is just something I don't know about linking that should be obvious, but I haven't found any references suggesting that it should be different linking a library in C++ vs. C, and linking other libraries (sox, for example) presents no difficulties with an identical setup.

  I have seen posts related to linking issues in Mac OS X 10.9 because of the change from libstdc++ to libc++, but adding -stdlib=libstdc++ or -stdlib=libc++ seems to make no difference. It also makes no difference to add -mmacosx-version-min=10.6 or 10.9.

  Any help is greatly appreciated.

• Extract subtitle by language code via ffmpeg

  7 mai 2023, par TrustFound

  I have a simple task - extract subtitle for exact language from tvshows.
For example, I want to extract English subtitles from Netflix's show.
As you know there're a few different types of subtitles : forced, full and SDH.
So I want to extract all of them if it has eng language code.

  


  To extract 1 subtitle from file I used this code for windows :

  


  FOR %%i IN (*.mkv) DO (ffmpeg.exe -i "%%i" -map 0:s:m:language:eng -c copy "%%~ni".eng.srt)


  


  It worked fine with 1 english subtitle per file. But if it contains 2, ffmpeg shows error

  


  


  SRT supports only a single subtitles stream

  


  


  ---

  


  MI is...

  


  

  • Stream #0:2(eng) : Subtitle : subrip

  


  • Stream #0:3(eng) : Subtitle : subrip

  


  • Stream #0:4(ara) : Subtitle : subrip

  


  • ...

  


  


  ---

  


  So I should set 2 or more output files. I tried to figure out how to do this and found similar threads on reddit and stacksoverflow. They said there's no way to do this without ffprobe.
So I used ffprobe to parse all subtitle tracks and their language code.

  


  FOR %%i IN (*.mkv) DO (ffprobe -loglevel error -select_streams s -show_entries stream=index:stream_tags=language -of csv=p=0 -i %%i > subs.txt)


  


  File contains this info :

  


  

  • 2,eng

  


  • 3,eng

  


  • 4,ara

  


  • ...

  


  


  ---

  


  As I understand I should use integers and set them values 2 and 3. I want to get output like this

  


  


  

  • MovieName.2.eng.srt

  


  • MovieName.3.eng.srt

  


  


  


  If it easier to extract all subs, let it be. I tried to do this too but I dont know how to set integers and use them :(
So what I should do ?
Thanks in advance

  


• DWT of frames by FFMPEG API

  13 mars 2015, par Vaigard

  How can I spend the DWT Y component is considered of H.264 video frame ? Do not quite understand the principle of filling the structure DWTContext and its schema. And is not a matter of AVFrame->data[0][x] values are already converted, for example by DCT ?

  Thanks and sorry for my English=)