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Autres articles (21)

  • Les formats acceptés

    28 janvier 2010, par

    Les commandes suivantes permettent d’avoir des informations sur les formats et codecs gérés par l’installation local de ffmpeg :
    ffmpeg -codecs ffmpeg -formats
    Les format videos acceptés en entrée
    Cette liste est non exhaustive, elle met en exergue les principaux formats utilisés : h264 : H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10 m4v : raw MPEG-4 video format flv : Flash Video (FLV) / Sorenson Spark / Sorenson H.263 Theora wmv :
    Les formats vidéos de sortie possibles
    Dans un premier temps on (...)

  • Ajouter notes et légendes aux images

    7 février 2011, par

    Pour pouvoir ajouter notes et légendes aux images, la première étape est d’installer le plugin "Légendes".
    Une fois le plugin activé, vous pouvez le configurer dans l’espace de configuration afin de modifier les droits de création / modification et de suppression des notes. Par défaut seuls les administrateurs du site peuvent ajouter des notes aux images.
    Modification lors de l’ajout d’un média
    Lors de l’ajout d’un média de type "image" un nouveau bouton apparait au dessus de la prévisualisation (...)

  • Keeping control of your media in your hands

    13 avril 2011, par

    The vocabulary used on this site and around MediaSPIP in general, aims to avoid reference to Web 2.0 and the companies that profit from media-sharing.
    While using MediaSPIP, you are invited to avoid using words like "Brand", "Cloud" and "Market".
    MediaSPIP is designed to facilitate the sharing of creative media online, while allowing authors to retain complete control of their work.
    MediaSPIP aims to be accessible to as many people as possible and development is based on expanding the (...)

Sur d’autres sites (4734)

  • Fastest way to extract raw Y' plane data from Y'Cb'Cr encoded video ?

    20 février 2024, par memeko

    I have a use-case where I'm extracting I-Frames from videos and turning them into perceptual hashes for later analysis.

    


    ⠀

    


    I'm currently using ffmpeg to do this with a command akin to :

    


    ffmpeg -skip_frame nokey -i 'in%~1.mkv' -vsync vfr -frame_pts true -vf 'keyframes/_Y/out%~1/%%06d.bmp'

    


    and then reading in the data from the resulting images.

    


    ⠀

    


    This is a bit wasteful as, to my understanding, ffmpeg does implicit YUV -> RGB colour-space conversion and I'm also needlessly saving intermediate data to disk.

    


    Most modern video codecs utilise chroma subsampling and have frames encoded in a Y'CbCr colour-space, where Y' is the luma component, and Cb Cr are the blue-difference, red-difference chroma components.

    


    Which in something like YUV420p used in h.264/h.265 video codecs is encoded as such :

    


    single YUV420p encoded frame

    


    Where each Y' value is 8 bits long and corresponds to a pixel.

    


    ⠀

    


    As I use gray-scale data for generating the perceptual hashes anyway, I was wondering if there is a way to simply grab just the raw Y' values from any given I-Frame into an array and skip all of the unnecessary conversions and extra steps ?

    


    (as the luma component is essentially equivalent to the grayscale data i need for generating hashes)

    


    I came across the -vf 'extractplanes=y' filter in ffmpeg that seems like it might do just that, but according to source :

    


    


    "...what is extracted by 'extractplanes' is not raw data of the (for example) Y plane. Each extracted is converted to grayscale. That is, the converted video data has YUV (or RGB) which is different from the input."

    


    


    which makes it seem like it's touching chroma components and doing some conversion anyway, in testing applying this filter didn't affect the processing time of the I-Frame extraction either.

    


    ⠀

    


    My script is currently written in Python, but I am in the process of migrating it to C++, so I would prefer any solutions pertaining to the latter.

    


    ffmpeg seems like the ideal candidate for this task, but I really am looking for whatever solution that would ingest the data fastest, preferably saving directly to RAM, as I'll be processing a large number of video files and discarding I-Frame luma pixel data once a hash has been generated.

    


    I would also like to associate each I-Frame with its corresponding frame number in the video.

    


  • Android Video color effect issue using FFMPEG [on hold]

    8 juin 2016, par umesh mishra

    I m facing one problem. when we use library for effect that i have mentioned below video is created only 1/3 of actual video size. please tell me what is issue. and also doesn’t work on marshmallow.
    https://github.com/krazykira/VidEffects/wiki/Permanent-video-effects

  • Evolution #2403 (Nouveau) : test : install

    11 novembre 2011, par jluc -

    Testant la surface de l’install et de la partie privée de spip3 voici quelques remarques : Install :

    les explications des champs de saisie sont souvent entre parentheses, ce qui est original, mais pas la première ligne de la première saisie. 1) ces parentheses apparaissent comme un maniérisme (...)

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