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• Icecast : always send a content-type

  11 novembre 2014, par Marvin Scholz

  Icecast : always send a content-type
  use a default (audio/mpeg for historical reason) if none. Required since Icecast 2.4.1
  
  Not using AVOption default because this breaks content-type warnings (needs to
  
  detect if no type was set by the user)
  Signed-off-by : Michael Niedermayer <michaelni@gmx.at>
  

  • [DH] libavformat/icecast.c

• What's the point of passing address of pointer to function that needs pointer to pointer ?

  16 août 2019, par Guerlando OCs

  I’m reading an example of ffmpeg decoding and it has the address of a pointer being passed to a function :

  static AVBufferRef *hw_device_ctx = NULL;
  
  
  
  
  
  if ((err = av_hwdevice_ctx_create(&hw_device_ctx, type,
  
                                    NULL, NULL, 0)) < 0) {

  What’s the point of passing the address of a pointer as an argument ?

  I understand that when we pass the pointer itself, if the pointer has address 0x123456, then the function is going to be able to modify what’s the object that is in this address. But when I pass the address of a pointer, I’m passing the address of where this pointer number is allocated ?

  If I understood right, I’m passing the address of the variable that stores 0x123456 ? Why the function needs it ?

  Also, suppose that I want to store hw_device_ctx in a unique_ptr like this :

  std::unique_ptr<avbufferred> hw_pointer;
  
  </avbufferred>

  How can I pass it to av_hwdevice_ctx_create ? Because I get an error when I do

  av_hwdevice_ctx_create(&hw_pointer.get(),...

  It says :

  expression must be an lvalue or a function designator

• Making new struct point to data from old struct without old struct deleting it

  14 août 2019, par Guerlando OCs

  Here’s how I decode videos in ffmpeg :

  AVFrame* avFrame;
  
  avFrame = av_frame_alloc();
  
  int receiveFrameResult = avcodec_receive_frame(avCodecContext, avFrame);

  Now my AVFrame struct has video data in its uint8_t * data field.

  I want to create my own struct myNewStruct which holds the data that AVFrame has in uint8_t * data[].

  The problem is that I don’t want to waste CPU time by copying value by value from avFrame->data to myNewStruct->buffer.

  I also can’t simply copy the data like this :

  myNewStruct.buffer[i] = new uint8_t;
  
  myNewStruct.buffer[i] = avFrame->data[i];

  because when avFrame gets destructed, it deletes the allocated data for data. I also can’t avoid deleting avFrame because it contains other unuseful fields that I don’t want in myNewStruct.

  How should I make myNewStruct->buffer point to the same data as avFrame->data points, but without worrying if avFrame is going to delete it ?

  UPDATE :

  AVFrame is from ffmpeg so I don’t have any control of its contents, therefore I cannot make its pointers of type shared_ptr