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  • Gestion générale des documents

    13 mai 2011, par

    MédiaSPIP ne modifie jamais le document original mis en ligne.
    Pour chaque document mis en ligne il effectue deux opérations successives : la création d’une version supplémentaire qui peut être facilement consultée en ligne tout en laissant l’original téléchargeable dans le cas où le document original ne peut être lu dans un navigateur Internet ; la récupération des métadonnées du document original pour illustrer textuellement le fichier ;
    Les tableaux ci-dessous expliquent ce que peut faire MédiaSPIP (...)

  • Encoding and processing into web-friendly formats

    13 avril 2011, par

    MediaSPIP automatically converts uploaded files to internet-compatible formats.
    Video files are encoded in MP4, Ogv and WebM (supported by HTML5) and MP4 (supported by Flash).
    Audio files are encoded in MP3 and Ogg (supported by HTML5) and MP3 (supported by Flash).
    Where possible, text is analyzed in order to retrieve the data needed for search engine detection, and then exported as a series of image files.
    All uploaded files are stored online in their original format, so you can (...)

  • Qualité du média après traitement

    21 juin 2013, par

    Le bon réglage du logiciel qui traite les média est important pour un équilibre entre les partis ( bande passante de l’hébergeur, qualité du média pour le rédacteur et le visiteur, accessibilité pour le visiteur ). Comment régler la qualité de son média ?
    Plus la qualité du média est importante, plus la bande passante sera utilisée. Le visiteur avec une connexion internet à petit débit devra attendre plus longtemps. Inversement plus, la qualité du média est pauvre et donc le média devient dégradé voire (...)

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  • HTML5 Video Presentations at LCA 2011

    http://blip.tv/file/get/Linuxconfau-TheLatestAndCoolestWithHTML5Video326.ogv
    10 février 2011, par silvia

    Working in the WHAT WG and the W3C HTML WG, you sometimes forget that all the things that are being discussed so heatedly for standardization are actually leading to some really exciting new technologies that not many outside have really taken note of yet. This week, during the Australian Linux (...)

  • FFmpeg decode H264 video too slowly

    17 décembre 2012, par user1158196

    I am currently working on a project on iPhone using FFMpeg. I can decode all the formats I need but when I want to play a h264 video, ffmpeg decodes frames too slowly.

    I tried to see where the problem is. I think that the options from the compilation of the library are good, decoding and displaying the frames are made ​​on different threads. In the end, it seems that it is the function avcodec_decode_video2 that takes too long (3 to 4 seconds to decode 30 frames).

  • Naive Sorenson Video 1 Encoder

    12 septembre 2010, par Multimedia Mike — General

    (Yes, the word is “naive” — or rather, “naïve” — not “native”. People always try to correct me when I use the word. Indeed, it should actually be written with 2 dots over the ‘i’ but who has a keyboard that can easily do that ?)

    At the most primitive level, programming a video encoder is about writing out a sequence of bits that the corresponding video decoder will understand. It’s sort of like creating a program — represented as a stream of opcodes — that will run on a given microprocessor or virtual machine. In fact, reading a video codec bitstream specification will reveal a lot of terminology along the lines of “transmitting information to the decoder” or “signaling the decoder to do xyz.”

    Creating a good encoder that will deliver decent quality at a reasonable bitrate is difficult. Creating a naive encoder that produces a technically compliant bitstream, not so much.



    When I wrote an FFmpeg encoder for Sorenson Video 1 (SVQ1), the first step was to just create a minimally compliant bitstream. The coarsest encoding mode that SVQ1 allows is to encode the average (mean) of each 16×16 block of samples. So I created an encoder that just encoded the mean of each block. Apple’s QuickTime Player was able to play the resulting video in all of its blocky glory. The result rather reminds me of the Super Nintendo’s mosaic effect.

    Level 5 blocks (mean-only 16×16 encoding) :



    Level 3 blocks (mean-only 8×8 encoding) :



    It’s one thing for your own decoder (in this case, FFmpeg’s own decoder) to be able to decode the data. The big test is whether the official decoder (in this case, Apple QuickTime Player) can decode the file.



    Now that’s a good feeling. After establishing that sort of baseline, it’s possible to adapt more and more features of the codec.

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