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• Concatenate sped up videos and normal speed ones using ffmpeg

  5 juillet 2020, par FlucTuAte.

  I have a python script that uses ffmpeg to cut different sections of a video. There are ones that i want to keep as-is, and i use this ffmpeg command for that :

  


  os.system((
      "ffmpeg "
      "-loglevel error "
      "-nostats "
      "-hide_banner "
      f"-ss {start / fps} "
      f"-i \"{uncutVideo}\" "
      f"-t {(end - start) / fps} "
      "-c copy "
      "-avoid_negative_ts make_zero "
      f"tmp\\out{processedClips}.mp4"
))


  


  Start and end are frame numbers, that's why i divide by fps.
Then I have the parts where I want to speed up the video. I use this command for that :

  


  os.system((
    "ffmpeg "
    "-loglevel error "
    "-nostats "
    "-hide_banner "
    f"-ss {start / fps} "
    f"-i \"{uncutVideo}\" "
    f"-t {(end - start) / fps / cfg.speed} "
    f"-vf \"setpts=PTS/{cfg.speed}\" "
    "-avoid_negative_ts make_zero "
    "-an "
    f"tmp\\out{processedClips}.mp4"
))


  


  After these are done I want to concatenate them using the concat demuxer :

  


  os.system((
    "ffmpeg "
    "-loglevel error "
    "-nostats "
    "-f concat "
    "-safe 0 "
    "-i videoClips.txt "
    "-c copy "
    f"\"{cfg.saveDir}\\{srcFileName}-Cut.mp4\""
))


  


  This runs fine, but in the output file there is a long pause when the sped up part would start. The last frame of the normal speed part is shown but the timeline shows that the video is playing. After the sped up part would have ended it shows the next normal speed part properly. This is what I see in VLC at least. I've also tried MPC-BE and MPC-HC. They also mess up but instead the sped up part is displayed properly and they pause right after. These pauses seem to be as long as the sped up part would be.

  


  What could cause this ?

  


  Any help is appreciated.

  


• lavc/h264dsp : R-V V 8-bit h264_idct_add16

  1er juillet 2024, par Rémi Denis-Courmont

  lavc/h264dsp : R-V V 8-bit h264_idct_add16
  While this *tends* to be faster than plain C, the performance numbers
  
  are all over the place, presuambly due to the conditional character of
  
  the main loop.
  Some additional micro-optimisations should be feasible after the
  
  underlying h264_idct_add and h264_idct_dc_add functions are also
  
  implemented. Then it will no longer be necesseray to stricly abide by
  
  the C ABI.
  

  • [DH] libavcodec/riscv/Makefile
  • [DH] libavcodec/riscv/h264dsp_init.c
  • [DH] libavcodec/riscv/h264idct_rvv.S

• hevc : deobfuscate slice/tile boundary handling for DBF

  27 juillet 2014, par Anton Khirnov

  hevc : deobfuscate slice/tile boundary handling for DBF
  Use named constants instead of magic numbers, avoid using variables with
  
  inverse meaning from what their name implies.
  

  • [DH] libavcodec/hevc.c
  • [DH] libavcodec/hevc.h
  • [DH] libavcodec/hevc_filter.c