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• ppc : reduce overreads when loading 8 pixels in altivec dsp functions

  13 février 2014, par Janne Grunau

  ppc : reduce overreads when loading 8 pixels in altivec dsp functions
  Altivec can only load naturally aligned vectors. To handle possibly
  
  unaligned data a second vector is loaded from an offset of the original
  
  location and the data is recovered through a vector permutation.
  
  Overreads are minimal if the offset for second load points to the last
  
  element of data. This is 7 for loading eight 8-bit pixels and overreads
  
  are reduced from 16 bytes to 8 bytes if the pixels are 64-bit aligned.
  
  For unaligned pixels the overread is reduced from 23 bytes to 15 bytes
  
  in the worst case.
  

  • [DH] libavcodec/ppc/dsputil_altivec.c

• [ffmpeg C++ API] : How to copy a music file's cover image into another music file ?

  22 avril 2022, par Ananta

  I am having difficulties in copying a source music file's cover image into a destination music file. These two music files are in different formats (i.e, either mp3, flac, wav, or wma, different sampling rate). How should I implement the code for this ? I created a minimal code for this task below :

  


  const char* src_path = "source.mp3";
const char* dest_path = "destination.flac";
AVPacket src_pic; 

// open the source path
AVFormatContext *src_ctx = avformat_alloc_context();
avformat_open_input(&src_ctx, src_path, NULL, NULL);

// find the first attached picture, if available
for (i = 0; i < src_ctx->nb_streams; i++)
   if (src_ctx->streams[i]->disposition & AV_DISPOSITION_ATTACHED_PIC) {
      src_pic = src_ctx->streams[i]->attached_pic;

// open the destination path
AVFormatContext *dest_ctx = avformat_alloc_context();
avformat_open_input(&dest_ctx, dest_path, NULL, NULL);

// Then, how to embed the 'src_pic' into 'dest_ctx'?

  


  


• snow : remove an obsolete av_assert2

  9 juillet 2015, par Andreas Cadhalpun

  snow : remove an obsolete av_assert2
  It asserts that the frame linesize is larger than 37, but it can be
  
  smaller and decoding such frames works.
  Before commit cc884a35 src_stride > 7*MB_SIZE was necessary, because the
  
  blocks were interleaved in the tmp buffer and the last block was added
  
  with an offset of 6*MB_SIZE.
  
  It was changed for src_stride <= 7*MB_SIZE to write the blocks
  
  sequentially, hence the larger tmp_step.
  
  After that the assert was only necessary to make sure that the buffer
  
  remained large enough.
  
  Since commit bd2b6b33 s->scratchbuf is used as tmp buffer.
  
  As part of commit 86e107a7 the minimal scratchbuf size was increased to
  
  256*7*MB_SIZE, which is enough for any src_stride <= 7*MB_SIZE.
  Also add a comment explaining the tmp_step calculation.
  Signed-off-by : Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>
  

  • [DH] libavcodec/snow.h