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• Weird cross platform support in ffmpeg

  31 mai 2022, par LmTinyToon

  I tried to build ffmpeg 4.4 library and link with it and I received multiple unresolved references. I came across on unusual architecture in ffmpeg for multiple platforms.The library has many places with code like this :

  


  void foo()
{
    // DO SOMETHING
    if (ARCH_MIPS) // maybe #if ARCH_MIPS (...) #endif should be used instead?
         foo_mips(...);
    if (ARCH_PPC)
        foo_ppc(c);
    if (ARCH_ARM)
         foo_arm(...);
    if (ARCH_AARCH64)
        foo_aarch64(...);
}


  


  This code leads to linker errors because there is no any stub methods for other platforms. I observed root MakeFile, it optionally includes platform dependent code for each library (path like $(LIB_SUBDIR)/$(ARCH)/MakeFile) where each foo_<arch></arch> is defined.

  


  So, how does it work ? In my opinion preprocessor directive #if should be used, otherwise we will receive unresolved reference on any platform. Maybe I missed something ? because this code appears frequently for example :

  


  

  1. utils.c : ff_yuv2rgb_init_tables_ppc

  


  2. swscale_unscaled.c : ff_get_unscaled_swscale_ppc, ff_get_unscaled_swscale_arm, ff_get_unscaled_swscale_aarch64

  


  3. cpu.c : ff_get_cpu_max_align_x86, ff_get_cpu_max_align_mips

  


  4. float_dsp.c : ff_float_dsp_init_aarch64, ff_float_dsp_init_ppc, ff_float_dsp_init_x86

  


  5. etc.

  


  


• libavfilter/x86/vf_gblur : correct the order of loop step

  16 septembre 2021, par Wu Jianhua

  libavfilter/x86/vf_gblur : correct the order of loop step
  The problem was caused by if the width of the processed block
  
  minus 1 is a multiple of the aligned number the instruction
  
  jle .bscale_scalar would skip the Optimized Loop Step, which
  
  will lead to an incorrect sampling when specifying steps more
  
  than 1. Move the Optimized Loop Step after .bscale_scalar to
  
  ensure the loop step is enabled.
  Signed-off-by : Wu Jianhua <jianhua.wu@intel.com>
  

  • [DH] libavfilter/x86/vf_gblur.asm

• Overlay Intro Titles/Video in FFMPEG and fix missing keyframes in one step

  23 juin 2021, par Digicrat

  How can I optimally apply an intro video (replacing the few seconds of video with a potentially missing keyframe, but keep the original audio) in one step ?

  


  I have a batch of input videos and a batch of associated (auto-generated) 'intro' videos to overlay on top of them (in this case, replacing the first 3 seconds of video). This is complicated by the fact that some of the input videos were cut in such a way that the first key frame is missing/corrupted in order to achieve the desired audio start point.

  


  My current working (but slow) two-step process is :

  


  ./ffmpeg.exe -i videoA.mp4 -force_key_frames "expr:gte(t,n_forced*3)" videoA-fixed.mp4

./ffmpeg.exe -i videoA-fixed.mp4 -i intro-videoA.mp4 -filter_complex "[0:0][1:0]overlay=enable='between(t,0,3)'[out]" -shortest -map [out] -map 0:1 -pix_fmt yuv420p -c:a copy -c:v libx264 -crf 18 mergedVideo.mp4


  


  I've tried adding the force_key_frames arguments to the latter command, but ffmpeg doesn't seem to like that. Placing it before the filter_complex yields an error "Stream specifier ':0' in filtergraph description [0:0][1:0]overlay=enable='between(t,0,3)'[out] matches no streams."