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• avformat/segment : Pass flags to child context

  11 avril 2016, par Michael Niedermayer

  avformat/segment : Pass flags to child context
  This is needed as the bitexact flag is not in the codecpar context, and thus not copied
  Signed-off-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] libavformat/segment.c

• ffmpeg in child process doesn't exit when parent closes pipe

  28 mars 2013, par user2221129

  This code snippet is from a pthread process. It is responsible for reading configuration/options to pass to ffmpeg. The data piped to ffmpeg is coming in on a ring buffer of video frames (as a proof of concept, in the final implementation these would be coming from a camera device). The parent writes to the child via a pipe established with dup2. The problem I'm having is that most of the time, the ffmpeg process doesn't seem to recognize the pipe has been closed by the parent (as strace shows the ffmpeg is in read). There are probably some unhandled mutex situations.

  #define CHILD_READ  writepipe[0]
  
  #define PARENT_WRITE    writepipe[1]
  
  #define MAX_VIDEO_BUFFERS 30
  
  
  
  static int last_frame_written = -1;
  
  static int buffer_size = -1;
  
  static void *video_buffer[MAX_VIDEO_BUFFERS];
  
  
  
  #define MAXTHREADS 2
  
  static pthread_t thread[MAXTHREADS];
  
  static int sigusr[MAXTHREADS];
  
  static int sigusr_thread[MAXTHREADS];
  
  
  
  #define MAXPARAMETERS 100
  
  
  
  void* encoder_thread(void *ptr)
  
  {
  
      int param;
  
      const char **parameters = new const char* [MAXPARAMETERS];
  
      ssize_t bytes_written_debug = 0;
  
  
  
      int writepipe[2] = {-1,-1};
  
      int last_frame_read = -1;
  
      pid_t   childpid;
  
  
  
      // xxx
  
      if ( 0 != pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, NULL) )
  
      {
  
          fprintf(stderr,"pthread_setcancelstate could not be set\n");
  
      }
  
  
  
      param = *(int*)ptr;
  
      fprintf(stderr,"param = %d\n", param);
  
  
  
      switch (param)
  
      {
  
          ...read config file and populate parameters for child call...
  
      }
  
  
  
      while ( last_frame_written == -1 )
  
      {
  
          fprintf(stderr,"ENCODER THREAD WAITING\n");
  
          sleep(1);
  
      }
  
  
  
      if ( pipe(writepipe) < 0 )
  
      {
  
          ...handle error case...
  
      }
  
  
  
  
  
      if ( (childpid = fork()) < 0)
  
      {
  
          fprintf(stderr,"child failed\n");
  
      }
  
      else if ( 0 == childpid )   /* in the child */
  
      {
  
          dup2(CHILD_READ,  STDIN_FILENO);
  
          //close(CHILD_READ); // doesn't seem to matter
  
          close(PARENT_WRITE);
  
  
  
          execv("/usr/bin/ffmpeg",(char **)parameters);
  
          return;
  
      }
  
      else                /* in the parent */
  
      {
  
          fprintf(stderr,"THREAD CHILD PID: %d\n",childpid);
  
          close(CHILD_READ);
  
  
  
          while ( last_frame_written > -1 && 0==sigusr_thread[param] )
  
          {
  
              if ( last_frame_read != last_frame_written )
  
              {
  
                  // send frame to child (ffmpeg)
  
                  last_frame_read = last_frame_written;
  
                  bytes_written_debug = write(PARENT_WRITE,video_buffer[last_frame_read], buffer_size);
  
                  if ( bytes_written_debug < 0 )
  
                  {
  
                      fprintf(stderr, "write error\n");
  
                      break;
  
                  }
  
              }
  
  
  
              usleep(10000); // assume ~100Hz rate
  
          }
  
  
  
  /// Problems begin now: no more data from main process,
  
  /// Shouldn't this close "close" the pipe created with dup2 and hence EOF ffmpeg?
  
          if ( close(PARENT_WRITE) )
  
          {
  
              fprintf(stderr,"\n\nclose failure! wtf?\n\n\n");
  
          }
  
  
  
  // debug sleep:
  
  // waiting 10 sec doesn't seem to help...
  
  // trying to give ffmpeg some time if it needs it
  
          sleep(10);
  
  
  
  // kill never fails here:
  
          if ( !kill(childpid,SIGINT) )
  
          {
  
              fprintf(stderr, "\n\nkill child %d\n", childpid);
  
          }
  
          else
  
          {
  
              fprintf(stderr, "\n\nkill failed for child %d\n", childpid);
  
          }
  
  
  
          fprintf(stderr,"\n\nwaiting\n\n\n");
  
          int status = 0;
  
  
  
  // wait forever (in most cases); ps -axw shows all the ffmpeg's
  
          wait(&status);
  
      }
  
  }
  
  
  
  
  
  
  
  
  
  int main()
  
  {
  
      ...
  
      for ( int i = 0; i < MAXTHREADS; ++i)
  
      {
  
          sigusr[i] = 0;
  
          sigusr_thread[i] = 0;
  
          param[i] = i;
  
          iret = pthread_create( &thread[i], NULL, encoder_thread, (void*) &param[i] );
  
      }
  
      ...
  
  
  
      // Maybe this is important to the pthread signaling?
  
      // Don't think so because thread's SIGINT isn't picked up by signal handler (not shown)
  
      sigemptyset(&set);
  
      sigaddset(&set, SIGHUP);
  
      sigaddset(&set, SIGINT);
  
      sigaddset(&set, SIGUSR1);
  
      sigaddset(&set, SIGUSR2);
  
      sigaddset(&set, SIGALRM);
  
  
  
      /* block out these signals */
  
      sigprocmask(SIG_BLOCK, &set, NULL);
  
  
  
      ...read file/populate frame buffer until file exhausted...
  
  
  
      fprintf(stderr, "waiting for threads to exit\n");
  
  
  
      for ( int i = 0; i < MAXTHREADS; ++i)
  
      {
  
          sigusr_thread[i] = 1;
  
          pthread_join( thread[i], NULL);
  
      }
  
      fprintf(stderr, "done waiting for threads to exit\n");
  
  
  
      ...
  
  
  
      return 0;
  
  }

  I've embedded comments and questions in the thread's parent code after the frame buffer read/write loop.

  Hope I've provided enough detail - stackoverflow posting noob ! Thank you.

• ffmpeg capture output from child window

  3 janvier 2013, par glitchyme

  using xwininfo -all I'm able to see the stats of any window, along with its child windows

  xwininfo: Window id: 0x3c000ba "Electro - The Slag & Prototype Raptor - Crescendo - YouTube - Mozilla Firefox"
  
  
  
    Root window id: 0xa8 (the root window) (has no name)
  
    Parent window id: 0xc001b8 (has no name)
  
       2 children:
  
       0x3c00175 (has no name): ()  1388x876+0+0  +52+24
  
          5 children:
  
          0x3d210ab (has no name): ()  854x510+225+197  +277+221
  
             1 child:
  
             0x3d210ac (has no name): ()  854x510+0+0  +277+221
  
                1 child:
  
                0x40404de "plugin-container": ("plugin-container" "Plugin-container")  854x510+0+0  +277+221
  
                   2 children:
  
                   0x40404e1 (has no name): ()  854x510+0+0  +277+221
  
                   0x40404df (has no name): ()  1x1+-1+-1  +276+220
  
          0x3ddbcf2 (has no name): ()  640x390+225+162  +277+186
  
             1 child:
  
             0x3ddbcf3 (has no name): ()  640x390+0+0  +277+186
  
                1 child:
  
                0x403d545 "plugin-container": ("plugin-container" "Plugin-container")  640x390+0+0  +277+186
  
                   2 children:
  
                   0x403d548 (has no name): ()  640x390+0+0  +277+186
  
                   0x403d546 (has no name): ()  1x1+-1+-1  +276+185
  
          0x3dac7f9 (has no name): ()  640x390+225+162  +277+186
  
             1 child:
  
             0x3dac7fa (has no name): ()  640x390+0+0  +277+186
  
                1 child:
  
                0x4039d8b "plugin-container": ("plugin-container" "Plugin-container")  640x390+0+0  +277+186
  
                   2 children:
  
                   0x4039d8e (has no name): ()  640x390+0+0  +277+186
  
                   0x4039d8c (has no name): ()  1x1+-1+-1  +276+185
  
          0x3c3f939 (has no name): ()  640x390+225+197  +277+221
  
             1 child:
  
             0x3c3f93a (has no name): ()  640x390+0+0  +277+221
  
                1 child:
  
                0x4011918 "plugin-container": ("plugin-container" "Plugin-container")  640x390+0+0  +277+221
  
                   2 children:
  
                   0x401191b (has no name): ()  640x390+0+0  +277+221
  
                   0x4011919 (has no name): ()  1x1+-1+-1  +276+220
  
          0x3c0d1dc (has no name): ()  1x1+0+97  +52+121
  
             1 child:
  
             0x3c0d1dd (has no name): ()  1x1+0+0  +52+121
  
                1 child:
  
                0x4002c1e "plugin-container": ("plugin-container" "Plugin-container")  1x1+0+0  +52+121
  
                   2 children:
  
                   0x4002c40 (has no name): ()  1x1+0+0  +52+121
  
                   0x4002c1f (has no name): ()  1x1+-1+-1  +51+120
  
       0x3c000bb (has no name): ()  1x1+-1+-1  +51+23
  
  
  
    Absolute upper-left X:  52
  
    Absolute upper-left Y:  24
  
    Relative upper-left X:  0
  
    Relative upper-left Y:  0
  
    Width: 1388
  
    Height: 876
  
    Depth: 24
  
    Visual: 0x23
  
    Visual Class: TrueColor
  
    Border width: 0
  
    Class: InputOutput
  
    Colormap: 0x20 (installed)
  
    Bit Gravity State: NorthWestGravity
  
    Window Gravity State: NorthWestGravity
  
    Backing Store State: NotUseful
  
    Save Under State: no
  
    Map State: IsViewable
  
    Override Redirect State: no
  
    Corners:  +52+24  -0+24  -0-0  ç0
  
    -geometry 1388x876-0-0
  
  
  
    Bit gravity: NorthWestGravity
  
    Window gravity: NorthWestGravity
  
    Backing-store hint: NotUseful
  
    Backing-planes to be preserved: 0xffffffff
  
    Backing pixel: 0
  
    Save-unders: No
  
  
  
    Someone wants these events:
  
        KeyPress
  
        KeyRelease
  
        ButtonPress
  
        ButtonRelease
  
        EnterWindow
  
        LeaveWindow
  
        PointerMotion
  
        Exposure
  
        VisibilityChange
  
        StructureNotify
  
        FocusChange
  
        PropertyChange
  
    Do not propagate these events:
  
    Override redirection?: No
  
  
  
    Window manager hints:
  
        Client accepts input or input focus: Yes
  
        Initial state is Normal State
  
        Displayed on desktop 0
  
        Window type:
  
            Normal
  
        Window state:
  
            Maximized Vert
  
            Maximized Horz
  
        Process id: 4087 on host jb
  
        Frame extents: 0, 0, 0, 0
  
  
  
    Normal window size hints:
  
        Program supplied minimum size: 18 by 97
  
        Program supplied maximum size: 1073741824 by 1073741824
  
        Program supplied window gravity: NorthWestGravity
  
    No zoom window size hints defined
  
  
  
    No window shape defined
  
    No border shape defined

  However, if I try capturing from the screen given the size and offset of the child window, then I risk losing data when another window floats ontop of it, I switch to another tab while recording, I resize the child window, or move the child window. Instead, I'd like to use ffmpeg to capture from specifically that child window.

  Ideas ? Tips ? Maybe some other hacks to accomplish this ? Thanks :)