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• C program cannot find function which included in header file

  17 juin 2013, par Juneyoung Oh

  I made program like this.

    1 #include 
  
    2 #include 
  
    3 #include 
  
    4 #include "libavformat/avformat.h"
  
    5 
  
    6 int main (int argc, char* argv[]){
  
    7         av_register_all();
  
    8         return 0;
  
    9 }

  My header file located in

  root@ubuntu:/home/juneyoungoh/getDuration# find / -name "avformat.h"
  
  /root/ffmpeg/libavformat/avformat.h
  
  /usr/local/include/libavformat/avformat.h

  then I run with gcc getDuration.c , but I show message like below.

  root@ubuntu:/home/juneyoungoh/getDuration# gcc getDuration.c 
  
  /tmp/ccwjonqH.o: In function `main':
  
  getDuration.c:(.text+0x10): undefined reference to `av_register_all'
  
  collect2: ld returned 1 exit status

  Frankly, I do not have any idea what makes this.

  Thanks for your answers.

  ========================== edited #1 ===========================

  when I "ls /usr/local/lib", I get this.

  root@ubuntu:/home/juneyoungoh/getDuration# ls /usr/local/lib/
  
  libavcodec.a   libavutil.a    libopus.la       libvpx.a   python2.7
  
  libavdevice.a  libfdk-aac.a   libpostproc.a    libx264.a
  
  libavfilter.a  libfdk-aac.la  libswresample.a  libyasm.a
  
  libavformat.a  libopus.a      libswscale.a     pkgconfig

  you can see libavformat.a in the very first of the last line.

  so if I command like what you suggest, I get below.

  /root/ffmpeg/libavformat/vqf.c:244: undefined reference to `av_free_packet'
  
  /usr/local/lib//libavformat.a(vqf.o): In function `add_metadata':
  
  /root/ffmpeg/libavformat/vqf.c:58: undefined reference to `av_malloc'
  
  /root/ffmpeg/libavformat/vqf.c:64: undefined reference to `av_dict_set'
  
  /usr/local/lib//libavformat.a(vqf.o): In function `vqf_read_header':
  
  /root/ffmpeg/libavformat/vqf.c:148: undefined reference to `av_dict_set'
  
  /root/ffmpeg/libavformat/vqf.c:208: undefined reference to `av_log'
  
  /root/ffmpeg/libavformat/vqf.c:216: undefined reference to `av_malloc'
  
  /root/ffmpeg/libavformat/vqf.c:170: undefined reference to `av_log'
  
  /root/ffmpeg/libavformat/vqf.c:121: undefined reference to `av_log'
  
  /root/ffmpeg/libavformat/vqf.c:184: undefined reference to `av_log'
  
  /root/ffmpeg/libavformat/vqf.c:136: undefined reference to `av_log'
  
  /usr/local/lib//libavformat.a(wavenc.o): In function `wav_write_trailer':
  
  /root/ffmpeg/libavformat/wavenc.c:210: undefined reference to `av_rescale'
  
  /usr/local/lib//libavformat.a(wavenc.o): In function `wav_write_packet':
  
  /root/ffmpeg/libavformat/wavenc.c:181: undefined reference to `av_log'

  It is too long, so I just post little part of that.

  I think all link of libavformat has been broken, But I do not know

  what can I do to fix that link.

  I have installed that their official link said.

  https://ffmpeg.org/trac/ffmpeg/wiki/UbuntuCompilationGuideQuantal

• How do i know in the ffmpeg arguments command line what each argument do ?

  24 mai 2013, par Revuen Ben Dror

  I have this code :

  public void Start(string FileName, Bitmap Sample_Bitmap, int BitmapRate )
  
          {
  
              p = new NamedPipeServerStream(pipename, PipeDirection.Out, 1, PipeTransmissionMode.Byte);
  
              byte[] b = new byte[1280 * 720 * 3]; // some buffer for the r g and b of pixels of an image of size 720p 
  
              System.Diagnostics.Process process = new System.Diagnostics.Process();
  
              process.StartInfo.FileName = @"D:\pipetest\pipetest\ffmpegx86\ffmpeg.exe";
  
              process.EnableRaisingEvents = false;
  
              process.StartInfo.WorkingDirectory = @"D:\pipetest\pipetest\ffmpegx86";
  
              process.StartInfo.Arguments = @"-f rawvideo -pix_fmt rgb24 -video_size 1280x720 -i
  
                                            \\.\pipe\mytestpipe -map 0 -c:v libx264 -r " + BitmapRate + " " + FileName;
  
              process.Start();
  
  
  
              process.StartInfo.UseShellExecute = false;
  
              process.StartInfo.CreateNoWindow = false;
  
              p.WaitForConnection();
  
          }

  So i know what BitmapRate do and the FileName but the rest of the arguments.

  What odes it mean the -f ? and the rawvideo is that from the decoders or encoders ? -i ? -c:v ? libx264 is a codec i guess and -r ?

  Tried to google for this arguments format but didn't find any.

  I have 4 text files lists :

  encoders.txt decoders.txt in both files i have rawvideo too.
  I have pixfmts.txt and fileformats.txt files.

  I want to build the arguments string from variables.

  So for example BitmapRate is int and FileName is string. And the rest of the arguments what types of variables each one i should put to get in the function ?

  For example

  the rgb24 what type is it ? the 1280x720 what type of variable it
  should be ?

• Compress video with ffmpeg programatically - i.e. using C libraries instead of command line or wrapper

  29 décembre 2014, par Mick

  I am trying to find some examples or guidelines that help show how to compress a video programatically using ffmpeg API’s (i.e. the C API’s not the command line).

  In other words I would like to achieve the equivalent of the following ffmpeg command line :

  ffmpeg -i inoutVideo.mp4 -strict experimental -acodec aac CompressedVideo_aac.mp4

  but using the appropriate API calls from a C program.

  I can already do this by creating a wrapper around the ’ffmpeg.c’ program but I am trying to understand how to achieve this with the C libraries directly.

  I realise I can simply(!) read the source code of ffmpeg.c to see what it does, but I was hoping for something that either provides and overview or a specific example for video compression.

  Any pointers gratefully appreciated.