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• v4l2 learning resources step by step [closed]

  5 août 2023, par Mark Watts

  I intend to learn how v4l2 works and how is a hw codec integrated to do decoding
What resources do i need and where to start ? i'm new to kernel space too

  


  

  1. Hardware board ? ( Raspberry pi or similar ?)

  


  2. Environment ( VMware ?)

  


  3. Example code with userspace Multimedia framework using v4l2 driver ( where can i see examples of this stuff that is already done ?)

  


  4. Documentation / turorials / videos

  


  


  Ive come across some videos from bootlin and the kernel documentation . I want to know how to approach it methodically.

  


• Anomalie #4348 : php 7.4 alpha1

  17 juin 2019

  Le warning sur time(’’) (nombre d’arguments incorrects) apparaît en PHP 7.3.
  Mais… je ne vois rien qui indique ce changement dans la doc de PHP.
  En tout cas, ça ne génère pas ces warning sur des fonctions utilisateurs.

  Si on met `declare(strict_types = 1) ;`, le Warning devient une `Fatal error : Uncaught ArgumentCountError : time()`,
  mais pareil, aucune erreur sur les appels erronés de fonctions utilisateurs…

  Je suppose donc que certaines fonctions PHP ont vu leur comportement changer si le nombre d’argument n’est pas correct.

• avcodec/nvenc : better surface allocation alghoritm, fix rc_lookahead

  21 novembre 2016, par Miroslav Slugeň

  avcodec/nvenc : better surface allocation alghoritm, fix rc_lookahead
  User selectable surfaces are not working correctly, if you set number of
  
  surfaces on cmdline, it will always use minimum 32 or 48 depends on
  
  selected resolution, but in nvenc it is not necessary to use so many
  
  surfaces.
  So from now you can define as low as 1 surface and nvenc will still
  
  work, it will ofcourse lower GPU memory usage by 95% and async_delay to zero
  That was the easy part, now littlebit more...
  Next part of this patch is to always prefer rc_lookahead to be more
  
  important for number of surfaces, than user defined surfaces value.
  
  Maximum rc_lookahead from nvidia documentation is 32, but could increase
  
  in future generations so there is no limit for this yet. Value
  
  async_depth is still accepted and prefered over rc_lookahead.
  There were also bug when you request more than rc_lookahead > 31, it
  
  will always set maximum 31, because surface numbers recalculation was
  
  after setting lookahead, which is now fixed.
  Results :
  
  If you set -rc_lookahead 32 and -bf 3 it will now use only 40 surfaces
  
  and lower GPU memory usage by 20%, also it will now increase PSNR by 0.012dB
  Two more comments :
  1. from my internal test, i don’t understand addition of 4 more surfaces
  
  when lookahead is calculated, i didn’t used this and everything works as
  
  with those 4 more extra surfaces, does anybody know what is going on
  
  there ? I looks like it was used for B frames which are calculated
  
  separately, because B frames maximum is 4.
  2. rc_lookahead is defined default to -1, but in test condition if
  
  (ctx->rc_lookahead) which sets lookahead it will be always true, i don’t
  
  know if this is intended behavior, so in default behavior is lookahead
  
  always on !
  This is default condition when rc_lokkahead is -1 (not defined on
  
  cmdline), whis is maybe something that is not intended :
  
  ctx->encode_config.rcParams.enableLookahead = 1 ;
  
  ctx->encode_config.rcParams.lookaheadDepth  = 0 ;
  
  ctx->encode_config.rcParams.disableIadapt   = 0 ;
  
  ctx->encode_config.rcParams.disableBadapt   = 0 ;
  Signed-off-by : Timo Rothenpieler <timo@rothenpieler.org>
  

  • [DH] libavcodec/nvenc.c