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  • Mediabox : ouvrir les images dans l’espace maximal pour l’utilisateur

    8 février 2011, par

    La visualisation des images est restreinte par la largeur accordée par le design du site (dépendant du thème utilisé). Elles sont donc visibles sous un format réduit. Afin de profiter de l’ensemble de la place disponible sur l’écran de l’utilisateur, il est possible d’ajouter une fonctionnalité d’affichage de l’image dans une boite multimedia apparaissant au dessus du reste du contenu.
    Pour ce faire il est nécessaire d’installer le plugin "Mediabox".
    Configuration de la boite multimédia
    Dès (...)

  • Les autorisations surchargées par les plugins

    27 avril 2010, par

    Mediaspip core
    autoriser_auteur_modifier() afin que les visiteurs soient capables de modifier leurs informations sur la page d’auteurs

  • Websites made ​​with MediaSPIP

    2 mai 2011, par

    This page lists some websites based on MediaSPIP.

Sur d’autres sites (10021)

  • avformat/matroskaenc : Don't waste bytes writing level 1 elements

    20 avril 2019, par Andreas Rheinhardt
    avformat/matroskaenc : Don't waste bytes writing level 1 elements

    Up until now, the length field of most level 1 elements has been written
    
using eight bytes, although it is known in advance how much space the
    
content of said elements will take up so that it would be possible to
    
determine the minimal amount of bytes for the length field. This
    
commit changes this.
    

    Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
    
Signed-off-by : James Almer <jamrial@gmail.com>
    • [DH] libavformat/matroskaenc.c
    • [DH] tests/fate/matroska.mak
    • [DH] tests/fate/wavpack.mak
    • [DH] tests/ref/fate/aac-autobsf-adtstoasc
    • [DH] tests/ref/fate/binsub-mksenc
    • [DH] tests/ref/fate/rgb24-mkv
    • [DH] tests/ref/lavf/mka
    • [DH] tests/ref/lavf/mkv
    • [DH] tests/ref/lavf/mkv_attachment
    • [DH] tests/ref/seek/lavf-mkv

  • 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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