Recherche avancée

Sur d’autres sites (4464)

• Stop doing this in your encoder comparisons

  14 juin 2010, par Dark Shikari — Uncategorized

  I’ll do a more detailed post later on how to properly compare encoders, but lately I’ve seen a lot of people doing something in particular that demonstrates they have no idea what they’re doing.

  PSNR is not a very good metric. But it’s useful for one thing : if every encoder optimizes for it, you can effectively measure how good those encoders are at optimizing for PSNR. Certainly this doesn’t tell you everything you want to know, but it can give you a good approximation of “how good the encoder is at optimizing for SOMETHING“. The hope is that this is decently close to the visual results. This of course can fail to be the case if one encoder has psy optimizations and the other does not.

  But it only works to begin with if both encoders are optimized for PSNR. If one optimizes for, say, SSIM, and one optimizes for PSNR, comparing PSNR numbers is completely meaningless. If anything, it’s worse than meaningless — it will bias enormously towards the encoder that is tuned towards PSNR, for obvious reasons.

  And yet people keep doing this.

  They keep comparing x264 against other encoders which are tuned against PSNR. But they don’t tell x264 to also tune for PSNR (–tune psnr, it’s not hard !), and surprise surprise, x264 loses. Of course, these people never bother to actually look at the output ; if they did, they’d notice that x264 usually looks quite a bit better despite having lower PSNR.

  This happens so often that I suspect this is largely being done intentionally in order to cheat in encoder comparisons. Or perhaps it’s because tons of people who know absolutely nothing about video coding insist on doing comparisons without checking their methodology. Whatever it is, it clearly demonstrates that the person doing the test doesn’t understand what PSNR is or why it is used.

  Another victim of this is Theora Ptalarbvorm, which optimizes for SSIM at the expense of PSNR — an absolutely great decision for visual quality. And of course if you just blindly compare Ptalarbvorm (1.2) and Thusnelda (1.1), you’ll notice Ptalarbvorm has much lower PSNR ! Clearly, it must be a worse encoder, right ?

  Stop doing this. And call out the people who insist on cheating.

• ffmpeg Unrecognized option 'preset' [closed]

  16 mai 2024, par Lalaluye

  Hello I just recently upgraded ffmpeg from 4.3.1 to 7.0 and getting the following error :

  


  my command is
ffmpeg -y -f image2pipe -framerate 24 -i pipe: -c:v libx264 -preset veryfast -crf 29 -pix_fmt yuv420

  


  and getting the below error :

  


  16 May 2024 06:43:28,979 [DEBUG] testIntent  (pool-7-thread-3) 
ffmpeg   built with gcc 7 (GCC)
16 May 2024 06:43:28,979 [DEBUG] testIntent  (pool-7-thread-3) 
configuration: --prefix=/local/p4clients/pkgbuild-JklBW/workspace/src/FFmpeg/build/private/install
16 May 2024 06:43:28,979 [DEBUG] testIntent  (pool-7-thread-3) 
ffmpeg   libavutil      59.  8.100 / 59.  8.100
16 May 2024 06:43:28,979 [DEBUG] testIntent  (pool-7-thread-3) 
ffmpeg   libavcodec     61.  3.100 / 61.  3.100
16 May 2024 06:43:28,979 [DEBUG] testIntent  (pool-7-thread-3) 
ffmpeg   libavformat    61.  1.100 / 61.  1.100
16 May 2024 06:43:28,979 [DEBUG] testIntent  (pool-7-thread-3) 
ffmpeg   libavdevice    61.  1.100 / 61.  1.100
16 May 2024 06:43:28,979 [DEBUG] testIntent  (pool-7-thread-3) 
ffmpeg   libavfilter    10.  1.100 / 10.  1.100
16 May 2024 06:43:28,979 [DEBUG] testIntent  (pool-7-thread-3) 
ffmpeg   libswscale      8.  1.100 /  8.  1.100
16 May 2024 06:43:28,979 [DEBUG] testIntent  (pool-7-thread-3) 
ffmpeg   libswresample   5.  1.100 /  5.  1.100
16 May 2024 06:43:28,979 [DEBUG] testIntent  (pool-7-thread-3) 
ffmpeg Unrecognized option 'preset'.



  


  Haven't found a resolution so far. Any help appreciated

  


• ffmpeg : Unrecognized option 'alpha_quality'

  16 avril 2024, par László Monda

  I want to make transparent videos work in Safari, which doesn't support WebM for this purpose but only H265 with alpha transparency.

  


  According to this post, I used Shutter Encoder, but only some of its versions work for this purpose on Mac.

  


  Instead of using Shutter Encoder on Mac, I want to use ffmpeg on my Linux PC. Shutter Encoder uses the following command in the background :

  


  ffmpeg -threads 0 -hwaccel none -i input.mov -c:v hevc_videotoolbox -alpha_quality 1 -b:v 1000k -profile:v main -level 5.2 -map v:0 -an -pix_fmt yuva420p -sws_flags bicubic -tag:v hvc1 -metadata creation_time=2024-04-14T14:53:08.734684Z -y output.mp4

  


  which yields the following output on my PC :

  


  ffmpeg version 4.4.2-0ubuntu0.22.04.1 Copyright (c) 2000-2021 the FFmpeg developers
  built with gcc 11 (Ubuntu 11.2.0-19ubuntu1)
  configuration: --prefix=/usr --extra-version=0ubuntu0.22.04.1 --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --arch=amd64 --enable-gpl --disable-stripping --enable-gnutls --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libcodec2 --enable-libdav1d --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libjack --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librabbitmq --enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libsrt --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzimg --enable-libzmq --enable-libzvbi --enable-lv2 --enable-omx --enable-openal --enable-opencl --enable-opengl --enable-sdl2 --enable-pocketsphinx --enable-librsvg --enable-libmfx --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libx264 --enable-shared
  WARNING: library configuration mismatch
  avcodec     configuration: --prefix=/usr --extra-version=0ubuntu0.22.04.1 --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --arch=amd64 --enable-gpl --disable-stripping --enable-gnutls --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libcodec2 --enable-libdav1d --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libjack --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librabbitmq --enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libsrt --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzimg --enable-libzmq --enable-libzvbi --enable-lv2 --enable-omx --enable-openal --enable-opencl --enable-opengl --enable-sdl2 --enable-pocketsphinx --enable-librsvg --enable-libmfx --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libx264 --enable-shared --enable-version3 --disable-doc --disable-programs --enable-libaribb24 --enable-libopencore_amrnb --enable-libopencore_amrwb --enable-libtesseract --enable-libvo_amrwbenc --enable-libsmbclient
  libavutil      56. 70.100 / 56. 70.100
  libavcodec     58.134.100 / 58.134.100
  libavformat    58. 76.100 / 58. 76.100
  libavdevice    58. 13.100 / 58. 13.100
  libavfilter     7.110.100 /  7.110.100
  libswscale      5.  9.100 /  5.  9.100
  libswresample   3.  9.100 /  3.  9.100
  libpostproc    55.  9.100 / 55.  9.100
Unrecognized option 'alpha_quality'.
Error splitting the argument list: Option not found


  


  When googling for "Unrecognized option 'alpha_quality'.", there are no results, which I find very odd.

  


  What's going on, and how can I make ffmpeg work for this purpose without Shutter Encoder ?