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• ffmpeg output parse in batch script

  3 juillet 2016, par vlad2005

  I am totally unfamiliar with scripts in Windows, but are forced to use such a script. I would like someone to help me with the following problem. I want to process the output from ffmpeg command to save information about access an webcam to be used later.
  More precisely command is following :

  ffmpeg -stats -hide_banner -list_devices true -f dshow -i dummy

  and output is like this :

  [dshow @ 02cec400] DirectShow video devices (some may be both video and audio devices)
  
  [dshow @ 02cec400]  "Microsoft LifeCam Studio"
  
  [dshow @ 02cec400]     Alternative name "@device_pnp_\\?\usb#vid_045e&pid_0772&mi_00#6&2a15e69b&0&0000#{65e8773d-8f56-11d0-a3b9-00a0c9223196}\global"
  
  [dshow @ 02cec400] DirectShow audio devices
  
  [dshow @ 02cec400]  "Desktop Microphone (3- Studio -"
  
  [dshow @ 02cec400]     Alternative name "@device_cm_{33D9A762-90C8-11D0-BD43-00A0C911CE86}\Desktop Microphone (3- Studio -"
  
  [dshow @ 02cec400]  "Line In (High Definition Audio "
  
  [dshow @ 02cec400]     Alternative name "@device_cm_{33D9A762-90C8-11D0-BD43-00A0C911CE86}\Line In (High Definition Audio "
  
  [dshow @ 02cec400]  "Microphone (High Definition Aud"
  
  [dshow @ 02cec400]     Alternative name "@device_cm_{33D9A762-90C8-11D0-BD43-00A0C911CE86}\Microphone (High Definition Aud"

  Typically, the first two occurence for ”Alternative name” from DirectShow correspond to video and audio, so for simplicity I want these two information saved in two variables.
  In this example is :

  @device_pnp_\\?\usb#vid_045e&pid_0772&mi_00#6&2a15e69b&0&0000#{65e8773d-8f56-11d0-a3b9-00a0c9223196}\global

  and

  @device_cm_{33D9A762-90C8-11D0-BD43-00A0C911CE86}\Desktop Microphone (3- Studio -

  Can someone more experienced to help me with this task ?
  Thanks in advance !

• How I can keep the camera preview fps same as that in CamcorderProfile.videoFrameRate

  30 janvier 2015, par suitianshi

  Say I have a video recording app. The user press down a start button to start recording and lifts finger up to stop. For some reason I am using Camera.onPreviewCallback to receive byte data from preview and output it as a mp4 file(with ffmpeg libs). Suppose the user long presses start button for 10s, and I get 100 frames totally.How can I let my video last for exactly 10 seconds ?

  There are some problems :

  1. The fps of camera preview is not stable, so I can only get total number of frames as well as the desired duration when the recording stops.
  2. ffmpeg requires a fps field to be set when encoding(). I don’t know if I could set the fps value at the last time(that is, when I get all frames). The documents says it should be set when calling avformat_write_header(), so I guess not.

• 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.