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• ffmpeg save difference between 2 videos to file

  10 août 2020, par 0x-1

  I'm currently trying to learn everything related to videos and encountered a problem that I need help with.

  


  The Question is : How can I save the difference between 2 videos to a seperate file with ffmpeg ?
  
For example here is the ffplay command I'm trying with :
(Source : https://superuser.com/questions/854543/how-to-compare-the-difference-between-2-videos-color-in-ffmpeg)

  


  ffplay -f lavfi "movie=left.mp4,setpts=PTS-STARTPTS,split=3[a0][a1][a2];
            movie=right.mp4,setpts=PTS-STARTPTS,split[b0][b1];
            [a0][b0]blend=c0_mode=difference[y];
            [a1]lutyuv=y=val:u=128:v=128[uv];
            [y][uv]mergeplanes=0x001112:yuv420p,pad=2*iw:ih:0:0[down];
            [a2][b1]hstack[up];[up][down]vstack"


  


  In this case I would want to have the bottom left video saved to a new file.
  
Can someone help me get together the right ffmpeg filter and explain the proccessing of ffmpeg ?

  


• no difference between h264 and h264_cuvid

  10 juillet 2020, par Ruslan Ablyazov

  I use libav to decode an RTSP stream. I tried two code options : with auto codec selection and with hardcoded codec.

  


  pCodec = avcodec_find_decoder (pFormatCtx->streams[p_InputVideoStreamIndex]->codecpar->codec_id);&#xA;//pCodec = avcodec_find_decoder_by_name ("h264_cuvid");&#xA;&#xA;LOG (info) &lt;&lt; "Video codec name" &lt;&lt; pCodec->name &lt;&lt; ". Full name:" &lt;&lt; (pCodec->long_name? PCodec->long_name: "<null>");&#xA;</null>

  


  The avcodec_find_decoder() function returns h264 codec. The problem is that the speed and load on the CPU when using h264 is no different from h264_cuvid. What could be the reason ? When I use h264_cuvid, the video card is loaded by 2-3% more.

  


  Video stream : 1920x1080 25 FPS (main and high profile).
Video card : NVIDIA Corporation GP107 [GeForce GTX 1050 Ti] (rev a1).
Processor : Intel (R) Core (TM) i5-8400 CPU @ 2.80GHz.

  


  Compilation config ffmpeg :

  


  ffmpeg version 4.3 Copyright (c) 2000-2020 the FFmpeg developers
  built with gcc 8 (Debian 8.3.0-6)
  configuration: --enable-gpl --enable-ladspa --enable-libpulse --enable-libsoxr --enable-libspeex --enable-avfilter --enable-avresample --enable-postproc --enable-pthreads --enable -libass --enable-libfreetype --enable-libmp3lame --enable-nonfree --disable-ffplay --enable-libxvid --enable-cuda --enable-cuda-nvcc --enable-cuda-sdk --enable- cuvid --enable-nvenc --enable-nonfree --enable-libnpp --enable-shared --extra-cflags = -I/usr/local/cuda/include --extra-ldflags = -L/usr/local/cuda/lib64


  


• ffmpeg AAC audio encoding with libfdk_aac : difference between -q:a and -vbr quality parameters ?

  16 juin 2020, par RocketNuts

  I want to encode an audio file to AAC, using libfdk_aac, and I'm wondering about the quality parameters. I want to use variable bitrate encoding, not constant bitrate.

  



  It seems I can specify the quality either with the -vbr N parameter (with N=1..5) like this :

  



  ffmpeg -i input.flac -acodec libfdk_aac -vbr 4 output.m4a


  



  Or using the -q:a N parameter (here N=0..9) like this :

  



  ffmpeg -i input.flac -acodec libfdk_aac -q:a 7 output.m4a


  



  How are these two related, is there a substantial difference ? Do specific -q:a values correspond to certain -vbr values, or is it a different encoding approach altogether ?