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Autres articles (57)

  • Contribute to documentation

    13 avril 2011

    Documentation is vital to the development of improved technical capabilities.
    MediaSPIP welcomes documentation by users as well as developers - including : critique of existing features and functions articles contributed by developers, administrators, content producers and editors screenshots to illustrate the above translations of existing documentation into other languages
    To contribute, register to the project users’ mailing (...)

  • Submit bugs and patches

    13 avril 2011

    Unfortunately a software is never perfect.
    If you think you have found a bug, report it using our ticket system. Please to help us to fix it by providing the following information : the browser you are using, including the exact version as precise an explanation as possible of the problem if possible, the steps taken resulting in the problem a link to the site / page in question
    If you think you have solved the bug, fill in a ticket and attach to it a corrective patch.
    You may also (...)

  • MediaSPIP 0.1 Beta version

    25 avril 2011, par

    MediaSPIP 0.1 beta is the first version of MediaSPIP proclaimed as "usable".
    The zip file provided here only contains the sources of MediaSPIP in its standalone version.
    To get a working installation, you must manually install all-software dependencies on the server.
    If you want to use this archive for an installation in "farm mode", you will also need to proceed to other manual (...)

Sur d’autres sites (4131)

  • A nice comparison of mics

    3 juin 2010

    DVEStore has done a great comparison of different types of microphones on video. Audio is a black art, and folks rarely put in the time to do A/B/C comparisons. We tend to just default to a set of mics that we’ve decided are "good enough" and then don’t go back to reevaluate.

  • Opera 10.60 Released with WebM Support

    7 juillet 2010, par noreply@blogger.com (John Luther)

    Congratulations to everyone at Opera Software for releasing version 10.60 of their browser, which supports WebM video playback. Downloads for Windows, Mac OS and Linux are available on the Opera download page.

  • Understanding the VP8 Token Tree

    7 juin 2010, par Multimedia Mike — VP8

    I got tripped up on another part of the VP8 decoding process today. So I drew a picture to help myself understand it. Then I went back and read David Conrad’s comment on my last post regarding my difficulty understanding the VP8 spec and saw that he ran into the same problem. Since we both experienced the same hindrance in trying to sort out this matter, I thought I may as well publish the picture I drew.

    VP8 defines various trees for decoding different syntax elements. There is one tree for decoding the tokens and it is expressed in the VP8 spec as such :

    PLAIN TEXT
    C :
    1. const tree_index coef_tree [2 * (num_dct_tokens - 1)] =
    2. {
    3.  -dct_eob, 2,        /* eob = "0"  */
    4.   -DCT_0, 4,        /* 0  = "10" */
    5.   -DCT_1, 6,        /* 1  = "110" */
    6.    8, 12,
    7.    -DCT_2, 10,      /* 2  = "11100" */
    8.     -DCT_3, -DCT_4,    /* 3  = "111010", 4 = "111011" */
    9.    14, 16,
    10.     -dct_cat1, -dct_cat2, /* cat1 = "111100", cat2 = "111101" */
    11.    18, 20,
    12.     -dct_cat3, -dct_cat4, /* cat3 = "1111100", cat4 = "1111101" */
    13.     -dct_cat5, -dct_cat6 /* cat4 = "1111110", cat4 = "1111111" */
    14. } ;

    Here is what the table looks like when you make a tree out of it (click for full size image) :



    The catch is that it makes no sense for an end-of-block (EOB) token to follow a 0 token since EOB already indicates that the remainder of the coefficients should be 0 anyway. Thus, the spec states that, "decoding of certain DCT coefficients may skip the first branch, whose preceding coefficient is a DCT_0." I confess, I didn’t understand what "skip the first branch" meant until I drew the tree.



    For those wondering why it might be sub-optimal (clarity-wise) for a spec to simply regurgitate vast chunks of C code, this makes a decent case. As you can see, the spec makes certain assumptions about how a binary tree should be organized in a static array (node n points to elements n*2 and n*2+1 as its branches ; leaves are either negative or 0). This is the second method I have seen ; another piece of code (not the VP8 spec) had the nodes in the first half of the array and pointed to leaves in the second half. There must be other arrangements.

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