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• FFmpeg compose, multi layers and filters, need kindly help 

  9 octobre 2019, par jadeshohy

  Pretty new to FFmpeg. We would like to use FFmpeg as a important part of an AR project.

  Currently, we find it is not easy for us.

  We want to compose the footages with FFmpeg.

  We got 5 layers, wanted to blend them with specific mode, like the things in After Effects.

  • layer-1/ [A.webm] video，vp9 codec, which has a transparent BG,has to be added as [normal mode]

  • layer-2/ [B.mp4] video, optical-flare things with black BG,has to be added as [screen mode]

  • layer-3/ [C.mp4] video, some motion graphic things with light BG,has to be added as [overlay mode]

  • layer-4/ [BG.MP4], backgound things, has to be added as [normal mode]

  After we blend those 4 (like pre-compose,use blend filter), we want to add another layer-5/[icon.png] which is the special icon.

  Layer-5 need to overlay the pre-compose. We have to overlay it at the special position (use overlay filter ?).

  Cause [icon.png] may change frequently. we want to deal with that after the 4 layer blending.

  But at the first step, when we set normal mode for layer-1 in blend filter, layer-1 [A.webm] lost the transparent BG，it gave us a black BG which block all other things.
  Blend filter can not handle the alpha channel of vp9 webm ?
  When we set the mode of layer-1 to screen mode,the translucent thing was not what we need.

  Could you please give us some commands to achieve the blend above ?

  The commands that are really work will be extremely useful for our FFmpeg initiation.

• How can I simulate ffmpeg's empty_moov option within code ?

  22 février 2014, par mczarnek

  Command-line ffmpeg has the ability to use an empty moov_atom at the beginning of a file.

  More info :
  http://www.ffmpeg.org/ffmpeg-formats.html#Options-3

  I would like to do the same thing, except within code. Anyone know how ?

• swscale/output : fix bilinear yuv2rgb chroma interpolation

  17 décembre 2024, par Niklas Haas

  swscale/output : fix bilinear yuv2rgb chroma interpolation
  These functions were divided into two special cases ; one assuming that
  
  uvalpha == 0, and the other assuming that uvalpha == 2048. This worked fine
  
  for simple 2x chroma upscaling but broke for e.g. yuv410p, non-centered chroma,
  
  or other special cases that involved non-aligned chroma filters.
  Fix it by instead dividing this check into two cases, a uvalpha==0 fast path
  
  and a uvalpha>0 general path. Instead of (A+B)/2 the general path now multiplies
  
  in the true uvalpha weight.
  I tried preserving the old fast path for the case of uvalpha == 2048, but this
  
  was significantly slower in practise versus having just one general path.
  
  However, we still need a uvalpha == 0 path for the unscaled case.
  Fixes : ticket #5083
  
  Signed-off-by : Niklas Haas <git@haasn.dev>
  
  Sponsored-by : Sovereign Tech Fund
  

  • [DH] libswscale/output.c