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  • Des sites réalisés avec MediaSPIP

    2 mai 2011, par

    Cette page présente quelques-uns des sites fonctionnant sous MediaSPIP.
    Vous pouvez bien entendu ajouter le votre grâce au formulaire en bas de page.

  • Le profil des utilisateurs

    12 avril 2011, par

    Chaque utilisateur dispose d’une page de profil lui permettant de modifier ses informations personnelle. Dans le menu de haut de page par défaut, un élément de menu est automatiquement créé à l’initialisation de MediaSPIP, visible uniquement si le visiteur est identifié sur le site.
    L’utilisateur a accès à la modification de profil depuis sa page auteur, un lien dans la navigation "Modifier votre profil" est (...)

  • Configurer la prise en compte des langues

    15 novembre 2010, par

    Accéder à la configuration et ajouter des langues prises en compte
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Sur d’autres sites (8691)

  • Drop libxvid rate control support for mpegvideo encoding

    3 décembre 2016, par Diego Biurrun
    Drop libxvid rate control support for mpegvideo encoding

    The feature has outlived is usefulness and complicates the code.
    • [DBH] libavcodec/Makefile
    • [DBH] libavcodec/libxvid.c
    • [DBH] libavcodec/libxvid.h
    • [DBH] libavcodec/libxvid_rc.c
    • [DBH] libavcodec/mpegvideo.h
    • [DBH] libavcodec/mpegvideo_enc.c

  • FFmpeg CRF control using x264 vs libvpx-vp9

    19 octobre 2016, par igon

    I have some experience using ffmpeg with x264 and I wanted to do a comparison with libvpx-vp9. I tested a simple single pass encoding of a raw video, varying the crf settings and presets both with x264 and libvpx-vp9. I am new to libvpx and I followed this and this carefully but I might have still specified wrong combination of parameters since the results I get do not make much sense to me.

    For x264 I did :

    ffmpeg -i test_video.y4m -c:v libx264 -threads 1 -crf <crf> -preset <preset> -y output.mkv 
    
</preset></crf>

    and obtained the following results :

    codec  , settings                        , time        , PSNR      ,bitrate
    
libx264,['-crf', '20', '-preset', 'fast'],13.1897280216, 42.938337 ,15728
    
libx264,['-crf', '20', '-preset', 'medium'],16.80494689, 42.879753 ,15287
    
libx264,['-crf', '20', '-preset', 'slow'],25.1142120361, 42.919206 ,15400
    
libx264,['-crf', '30', '-preset', 'fast'],8.79047083855, 37.975141 ,4106
    
libx264,['-crf', '30', '-preset', 'medium'],9.936599016, 37.713778 ,3749
    
libx264,['-crf', '30', '-preset', 'slow'],13.0959510803, 37.569511 ,3555

    This makes sense to me, given a crf value you get a value of PSNR and changing the preset can decrease the bitrate but increase the time to encode.

    For libvpx-vp9 I did :

    ffmpeg -i test_video.y4m -c:v libvpx-vp9 -threads 1 -crf <crf> -cpu-used <effort> -y output.mkv 
    
</effort></crf>

    First of all I thought from tutorials online that the -cpu-used option is equivalent to -preset in x264. Is that correct ? If so what is the difference with -quality ? Furthermore since the range goes from -8 to 8 I assumed that negative values where the fast options while positive values the slowest. Results I get are very confusing though :

    codec     , settings                      , time        , PSNR     ,bitrate
    
libvpx-vp9,['-crf', '20', '-cpu-used', '-2'],19.6644911766,32.54317,571
    
libvpx-vp9,['-crf', '20', '-cpu-used', '0'],176.670887947,32.69899,564
    
libvpx-vp9,['-crf', '20', '-cpu-used', '2'],20.0206270218,32.54317,571
    
libvpx-vp9,['-crf', '30', '-cpu-used', '-2'],19.7931578159,32.54317,571
    
libvpx-vp9,['-crf', '30', '-cpu-used', '0'],176.587754965,32.69899,564
    
libvpx-vp9,['-crf', '30', '-cpu-used', '2'],19.8394429684,32.54317,571

    Bitrate is very low and PSNR seems unaffected by the crf setting (and very low compared to x264). The -cpu-used setting has very minimal impact and also seems that -2 and 2 are the same option.. What am I missing ? I expected libvpx to take more time to encode (which is definitely true) but at the same time higher quality transcodes. What parameters should I use to
    have a fair comparison with x264 ?

    Edit : Thanks to @mulvya and this doc I figured that to work in crf mode with libvpx I have to add -b:v 0. I re-ran my tests and I get :

        codec     , settings                                 , time        , PSNR     ,bitrate
    
libvpx-vp9,['-crf', '20', '-b:v', '0', '-cpu-used', '-2'],57.6835780144,45.111158,17908
    
libvpx-vp9,['-crf', '20', '-b:v', '0', '-cpu-used', '0'] ,401.360313892,45.285367,17431
    
libvpx-vp9,['-crf', '20', '-b:v', '0', '-cpu-used', '2'] ,57.4941239357,45.111158,17908
    
libvpx-vp9,['-crf', '30', '-b:v', '0', '-cpu-used', '-2'],49.175855875,42.588178,11085
    
libvpx-vp9,['-crf', '30', '-b:v', '0', '-cpu-used', '0'] ,347.158324957,42.782194,10935
    
libvpx-vp9,['-crf', '30', '-b:v', '0', '-cpu-used', '2'] ,49.1892938614,42.588178,11085

    PSNR and bitrate went up significantly by adding -b:v 0

  • FFmpeg CRF control using x264 vs libvpx-vp9

    19 octobre 2016, par igon

    I have some experience using ffmpeg with x264 and I wanted to do a comparison with libvpx-vp9. I tested a simple single pass encoding of a raw video, varying the crf settings and presets both with x264 and libvpx-vp9. I am new to libvpx and I followed this and this carefully but I might have still specified wrong combination of parameters since the results I get do not make much sense to me.

    For x264 I did :

    ffmpeg -i test_video.y4m -c:v libx264 -threads 1 -crf <crf> -preset <preset> -y output.mkv 
    
</preset></crf>

    and obtained the following results :

    codec  , settings                        , time        , PSNR      ,bitrate
    
libx264,['-crf', '20', '-preset', 'fast'],13.1897280216, 42.938337 ,15728
    
libx264,['-crf', '20', '-preset', 'medium'],16.80494689, 42.879753 ,15287
    
libx264,['-crf', '20', '-preset', 'slow'],25.1142120361, 42.919206 ,15400
    
libx264,['-crf', '30', '-preset', 'fast'],8.79047083855, 37.975141 ,4106
    
libx264,['-crf', '30', '-preset', 'medium'],9.936599016, 37.713778 ,3749
    
libx264,['-crf', '30', '-preset', 'slow'],13.0959510803, 37.569511 ,3555

    This makes sense to me, given a crf value you get a value of PSNR and changing the preset can decrease the bitrate but increase the time to encode.

    For libvpx-vp9 I did :

    ffmpeg -i test_video.y4m -c:v libvpx-vp9 -threads 1 -crf <crf> -cpu-used <effort> -y output.mkv 
    
</effort></crf>

    First of all I thought from tutorials online that the -cpu-used option is equivalent to -preset in x264. Is that correct ? If so what is the difference with -quality ? Furthermore since the range goes from -8 to 8 I assumed that negative values where the fast options while positive values the slowest. Results I get are very confusing though :

    codec     , settings                      , time        , PSNR     ,bitrate
    
libvpx-vp9,['-crf', '20', '-cpu-used', '-2'],19.6644911766,32.54317,571
    
libvpx-vp9,['-crf', '20', '-cpu-used', '0'],176.670887947,32.69899,564
    
libvpx-vp9,['-crf', '20', '-cpu-used', '2'],20.0206270218,32.54317,571
    
libvpx-vp9,['-crf', '30', '-cpu-used', '-2'],19.7931578159,32.54317,571
    
libvpx-vp9,['-crf', '30', '-cpu-used', '0'],176.587754965,32.69899,564
    
libvpx-vp9,['-crf', '30', '-cpu-used', '2'],19.8394429684,32.54317,571

    Bitrate is very low and PSNR seems unaffected by the crf setting (and very low compared to x264). The -cpu-used setting has very minimal impact and also seems that -2 and 2 are the same option.. What am I missing ? I expected libvpx to take more time to encode (which is definitely true) but at the same time higher quality transcodes. What parameters should I use to
    have a fair comparison with x264 ?

    Edit : Thanks to @mulvya and this doc I figured that to work in crf mode with libvpx I have to add -b:v 0. I re-ran my tests and I get :

        codec     , settings                                 , time        , PSNR     ,bitrate
    
libvpx-vp9,['-crf', '20', '-b:v', '0', '-cpu-used', '-2'],57.6835780144,45.111158,17908
    
libvpx-vp9,['-crf', '20', '-b:v', '0', '-cpu-used', '0'] ,401.360313892,45.285367,17431
    
libvpx-vp9,['-crf', '20', '-b:v', '0', '-cpu-used', '2'] ,57.4941239357,45.111158,17908
    
libvpx-vp9,['-crf', '30', '-b:v', '0', '-cpu-used', '-2'],49.175855875,42.588178,11085
    
libvpx-vp9,['-crf', '30', '-b:v', '0', '-cpu-used', '0'] ,347.158324957,42.782194,10935
    
libvpx-vp9,['-crf', '30', '-b:v', '0', '-cpu-used', '2'] ,49.1892938614,42.588178,11085

    PSNR and bitrate went up significantly by adding -b:v 0

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