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• How to choose gpu among multiple nvidia gpu in ffmpeg 3.2.0 ?

  4 mai 2017, par jsBaek

  i’m currently using two nvidia p4 graphic cards.

  In previous version of ffmpeg(before 3.2.0), i could choose specific gpu card by using options "-gpu 0 or 1 etc".

  In current version, however, there’s no option for selecting gpu card.

  Actually there’s "gpu" option specified in nvenc_h264.c or nvenc_hevc.c.

  But in nvenc.c file, there’s no code that uses "gpu" option.

  Is there any way that i can choose specific card ?

  How load balancing between two cards is done ?

  Is it done in driver level ?

  Thank you.

• avfilter/phase_template : Fix left-shift of negative numbers

  6 novembre 2022, par Andreas Rheinhardt

  avfilter/phase_template : Fix left-shift of negative numbers
  Affected the filter-phase FATE-test.
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
  

  • [DH] libavfilter/phase_template.c

• swresample/resample : speed up build_filter by 50%

  4 novembre 2015, par Ganesh Ajjanagadde

  swresample/resample : speed up build_filter by 50%
  This speeds up build_filter by 50%. This gain should be pretty
  
  consistent across all architectures and platforms.
  Essentially, this relies on a observation that the filters have some
  
  even/odd symmetry that may be exploited during the construction of the
  
  polyphase filter bank. In particular, phases (scaled to [0, 1]) in [0.5, 1] are
  
  easily derived from [0, 0.5] and expensive reevaluation of function
  
  points are unnecessary. This requires some rather annoying even/odd
  
  bookkeeping as can be seen from the patch.
  I vaguely recall from signal processing theory more general symmetries allowing even greater
  
  optimization of the construction. At a high level, "even functions"
  
  correspond to 2, and one can imagine variations. Nevertheless, for the sake
  
  of some generality and because of existing filters, this is all that is
  
  being exploited.
  Currently, this patch relies on phase_count being even or (trivially) 1,
  
  though this is not an inherent limitation to the approach. This
  
  assumption is safe as phase_count is 1 << phase_bits, and is hence a
  
  power of two. There is no way for user API to set it to a nontrivial odd
  
  number. This assumption has been placed as an assert in the code.
  To repeat, this assumes even symmetry of the filters, which is the most common
  
  way to get generalized linear phase anyway and is true of all currently
  
  supported filters.
  As a side note, accuracy should be identical or perhaps slightly better
  
  due to this "forcing" filter symmetries leading to a better phase
  
  characteristic. As before, I can’t test this claim easily, though it may
  
  be of interest.
  Patch tested with FATE.
  Sample benchmark (x86-64, Haswell, GNU/Linux) :
  test : swr-resample-dblp-44100-2626
  new :
  
  527376779 decicycles in build_filter(loop 1000),     256 runs,      0 skips
  
  524361765 decicycles in build_filter(loop 1000),     512 runs,      0 skips
  
  516552574 decicycles in build_filter(loop 1000),    1024 runs,      0 skips
  old :
  
  974178658 decicycles in build_filter(loop 1000),     256 runs,      0 skips
  
  972794408 decicycles in build_filter(loop 1000),     512 runs,      0 skips
  
  954350046 decicycles in build_filter(loop 1000),    1024 runs,      0 skips
  Note that lower level optimizations are entirely possible, I focussed on
  
  getting the high level semantics correct. In any case, this should
  
  provide a good foundation.
  Reviewed-by : Michael Niedermayer <michael@niedermayer.cc>
  
  Signed-off-by : Ganesh Ajjanagadde <gajjanagadde@gmail.com>
  

  • [DH] libswresample/resample.c