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• libFLAC : CPUID detecion improvements.

  28 juin 2014, par Erik de Castro Lopo

  libFLAC : CPUID detecion improvements.
  According to docs, it’s incorrect to just call CPUID with EAX=1.
  
  One must to ensure that this value is supported.
  CPUs that don’t support CPUID level 1 are very old, but...
  
  if FLAC tests CPUID presence it should also test CPUID level support.
  Also the function FLAC__cpu_have_cpuid_asm_ia32 was simplified
  
  according to the docs at Intel website and in Wikipedia.
  Patch-from : lvqcl <lvqcl.mail@gmail.com>
  

  • [DH] src/libFLAC/cpu.c
  • [DH] src/libFLAC/ia32/cpu_asm.nasm

• Writing a Custom Blend for Softlight

  21 mai 2020, par Jonas

  Lately I've been messing around with ffmpeg's blending modes and noticed their algorithms are not entirely the same as in Photoshop. I'm interested in Softlight blend and will use it as an example to illustrate my issue.

  



  First thing's first, I was able to mimic Photoshop's softlight with the blend and geq filters, but it's painfully slow with video inputs. Problem of geq I guess.

  



  ffmpeg -i top.png -i bottom.png -filter_complex "[0]format=rgba[a];[1]format=rgba,split[b][b2];[a][b]blend=all_expr='if(lt(A\,0.5)\,(2*B*A+(B*B)*(1-2*A))/255\,(2*B*(1-A)+sqrt(B)*(2*A-1))/255)':c3_expr=A,geq=a='p(X\,Y)':r='min(255\,p(X\,Y))':g='min(255\,p(X\,Y))':b='min(255\,p(X\,Y))'[tmp];[b2][tmp]overlay[out]" -map [out] output.png


  



  So it occurred to me that I'd be better off building ffmpeg from source adding in the PS softlight blend formula (note that in the formula a is the bottom layer and b is top, while in the code snippets it's the reverse).

  



  

  



  I'm introducing changes to vf_blend.c file, line 263

  



  DEFINE_BLEND8(softlight,  (A > 127) ? B + (255 - B) * (A - 127.5) / 127.5 * (0.5 - fabs(B - 127.5) / 255): B - B * ((127.5 - A) / 127.5) * (0.5 - fabs(B - 127.5)/255))


  



  and making it

  



  DEFINE_BLEND8(softlight,   (A < 127) ? (2*B*A+(B*B)*(127.5-2*A))/255 : (2*B*(127.5-A)+sqrt(B)*(2*A-127.5))/255)


  



  Result was quite close but not exactly what I want (has a green tint on the output). My question is how can I change that line of code to match the above formula and get the desired softlight blend ?

  


• How to map ffmpeg formats to MIME types and file extensions ?

  12 août 2020, par odigity

  Anyone know of a reference for mapping ffmpeg format values to MIME types and recommended file extension ? My google attempt failed to turn up anything.

  



  I did manually put together a small list with guess-work and clues from Wikipedia, IANA, and the Mozilla Developer Network for the subset of formats that I encountered in my video input test collection :

  



  ffmpeg Format             Extension  MIME Type
───────────────────────   ─────────  ────────────────────── 
asf                       asf        application/vnd.ms-asf
avi                       avi        video/x-msvideo
flv                       flv        video/x-flv
matroska,webm             webm       video/webm
m4v                       m4v        video/x-m4v
mov,mp4,m4a,3gp,3g2,mj2   mp4        video/mp4
mpeg                      mpeg       video/mpeg
mpegts                    mpeg       video/mpeg
mpegvideo                 mpeg       video/mpeg
ogg                       ogv        video/ogg
matroska                  mkv        video/x-matroska
webm                      webm       video/webm


  



  No idea if I've made the right calls, though.

  



  (The test files already have file extensions, but I'm operating on the assumption that the extension of a file a user uploads is irrelevant, and that the file should be renamed based on ffprobe and intelligent mapping...)