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• vc2enc : prevent random data

  5 mai 2016, par Christophe Gisquet

  vc2enc : prevent random data
  The slice prefix is 0 in the reference encoder and the decoder ignores it.
  
  Writing 0 there seems like the best temporary solution.
  The padding could have contained uninitialized data, but reference VC2
  
  encoders put 0xFF there, hence the memset value.
  Overall this allows producing bistreams with no random data for use by fate.
  

  • [DH] libavcodec/vc2enc.c

• How do I pre-allocate the memory for libavcodec to write decoded frame data ?

  18 décembre 2018, par codemonkey

  I am trying to decode a video with libav by following the demo code : here

  I need to be able to control where the frame data in pFrame->data[0] is stored. I have tried setting pFrame->data to my own buffer as follows :

  // Determine required buffer size and allocate buffer 
  
  int numBytes = av_image_get_buffer_size(pixFmt, width, height, 1); 
  
  (uint8_t*) dataBuff = (uint8_t*) malloc (numBytes * sizeof(uint8_t)); 
  
  
  
  // Assign buffer to image planes in pFrame
  
  av_image_fill_arrays(frame->data, frame->linesize, dataBuff, pixFmt, width,
  
  height, 1);

  While this does set pFrame->data to be dataBuff (if I print their addresses, they are the same), this call ret = avcodec_receive_frame(pCodecContext, pFrame) to receive the decoded data always writes the data to a different address. It seems to manage its own memory somewhere in the underlying API and ignores the dataBuff that I assigned to pFrame right before.

  So I’m stuck—how can I tell libav to write decoded frame data to memory that I pre-allocate ? I’ve seen people ask similar questions online and in the libav forum but haven’t been able to find an answer.

  Many thanks 

• FFmpeg API : parse raw movie packet data into AVPacket

  7 novembre 2011, par Andrea3000

  If you have a movie file and you need to extract frame (packet) from it, it's simply a matter of writing :

  avformat_open_input(AVFormatContext **ps, const char *filename, AVInputFormat *fmt, AVDictionary **options);
  
  
  
  ...
  
  
  
  AVPacket packet;
  
  av_read_frame(formatContext, &packet);

  But what if I don't have the movie file but only unparsed, raw packet data ? These raw packet data are the same as the raw data contained into the movie file but I don't access them throught avformat_open_input and therefore I can't use av_read_frame so FFmpeg doesn't parse them.

  How can I parse this raw data in order to build the corresponding AVPacket ?
  I need to obtain an AVPacket identical to the ones provided by av_read_frame.