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• avcodec/dcahuff : Combine tables, use ff_init_vlc_from_lengths()

  6 septembre 2022, par Andreas Rheinhardt

  avcodec/dcahuff : Combine tables, use ff_init_vlc_from_lengths()
  Up until now, initializing the dca VLC tables uses ff_init_vlc_sparse()
  
  with length tables of type uint8_t and code tables of type uint16_t
  
  (except for the LBR tables, which uses length and symbols of type
  
  uint8_t ; these tables are interleaved). In case of the quant index
  
  codebooks these arrays were accessed via tables of pointers to the
  
  individual tables.
  This commit changes this : First, we switch to ff_init_vlc_from_lengths()
  
  to replace the uint16_t code tables by uint8_t symbol tables
  
  (this necessitates ordering the tables from left-to-right in the tree
  
  first). These symbol tables are interleaved with the length tables.
  Furthermore, these tables are combined in order to remove the table of
  
  pointers to individual tables, thereby avoiding relocations (for x64
  
  elf systems this amounts to 96*24B = 2304B saved in .rela.dyn) and
  
  saving 1280B from .data.rel.ro (for 64bit systems). Meanwhile the
  
  savings in .rodata amount to 2709 + 2 * 334 = 3377B. Due to padding
  
  the actual savings are higher : The ELF x64 ABI requires objects >= 16B
  
  to be padded to 16B and lots of the tables have 2^n + 1 elements
  
  of these were from replacing uint16_t codes with uint8_t symbols ;
  
  the rest was due to the fact that combining the tables eliminated
  
  padding (the ELF x64 ABI requires objects >= 16B to be padded to 16B
  
  and lots of the tables have 2^n + 1 elements)). Taking this into
  
  account gives savings of 4548B. (GCC by default uses an even higher
  
  alignment (controlled by -malign-data) ; for it the savings are 5748B.)
  These changes also necessitated to modify the init code for
  
  the encoder tables.
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
  

  • [DH] libavcodec/dcaenc.c
  • [DH] libavcodec/dcahuff.c
  • [DH] libavcodec/dcahuff.h

• FFMPEG loop to trim silence at beginning and end of file

  23 août 2021, par Juan Pablo

  I'm trying to take a folder that contains mp3 and wave files and trim the silence at the beginning and the end in all the individual files.

  


  for f in *.{mp3,wav}; do ffmpeg -i "$f" -af "silenceremove=start_periods=1:start_duration=1:start_threshold=-60dB:detection=peak,aformat=dblp,areverse,silenceremove=start_periods=1:start_duration=1:start_threshold=-60dB:detection=peak,aformat=dblp,areverse" "outputs/${f%.*}.mp3"; done


  


  I keep receiving an error that f was unexpected. Can someone tell me what I'm doing wrong ?

  


• lavc/vorbisdec : use intermediate variables

  19 septembre 2022, par Rémi Denis-Courmont

  lavc/vorbisdec : use intermediate variables
  The compiler cannot infer that the two float vectors do not alias,
  
  causing unnecessary extra loads and serialisation. This patch caches
  
  the two input values in local variables so that compiler can optimise
  
  individual loop iterations.
  

  • [DH] libavcodec/vorbisdec.c