Plop,

Si tu trouves des infos, je suis preneur
Pour ma part, ce que je propose qui reste assez barbare mais qui devrait marcher, ce serait de faire executer un MEL avant ton rendu.
Vu qu'a priori dans la les options de rendu de MR nous avons :

C:>Render -r mr -help

Usage: Render [options] filename
       where "filename" is a Maya ASCII or a Maya binary file.

Common options:
  -help              Print help
  -test              Print Mel commands but do not execute them
  -verb              Print Mel commands before they are executed
  -keepMel           Keep the temporary Mel file
  -listRenderers     List all available renderers
  -renderer string   Use this specific renderer
  -r string          Same as -renderer
  -proj string       Use this Maya project to load the file
  -log string        Save output into the given file

Specific options for renderer "mr": Mentalray renderer

General purpose flags:
  -rd path             Directory in which to store image files
  -im filename         Image file output name
  -of string           Output image file format. See the Render Settings window
        to find available formats

Frame numbering options
  -s float             Starting frame for an animation sequence
  -e float             End frame for an animation sequence
  -b float             By frame (or step) for an animation sequence
  -pad int             Number of digits in the output image frame file name
        extension
  -rfs int             Renumber Frame Start: number for the first image when
        renumbering frames
  -rfb int             Renumber Frame By (or step) used for renumbering frames
  -fnc int             File Name Convention: any of name, name.ext, ... See the
        Render Settings window to find available options. Use namec and
        namec.ext for Multi Frame Concatenated formats. As a shortcut,
        numbers 1, 2, ... can also be used

Camera options
  -cam name            Specify which camera to be rendered
  -rgb boolean         Turn RGB output on or off
  -alpha boolean       Turn Alpha output on or off
  -depth boolean       Turn Depth output on or off
  -iip                 Ignore Image Planes. Turn off all image planes before
        rendering

Resolution options
  -x int               Set X resolution of the final image
  -y int               Set Y resolution of the final image
  -percentRes float    Renders the image using percent of the resolution
  -ard float           Device aspect ratio for the rendered image

Render Layers and Passes:
  -rl boolean|name(s)  Render each render layer separately
  -rp boolean|name(s)  Render passes separately. 'all' will render all passes
  -sel boolean|name(s) Selects which objects, groups and/or sets to render

Mel callbacks
  -preRender string    Mel code executed before rendering
  -postRender string   Mel code executed after rendering
  -preLayer string     Mel code executed before each render layer
  -postLayer string    Mel code executed after each render layer
  -preFrame string     Mel code executed before each frame
  -postFrame string    Mel code executed after each frame
  -pre string          Obsolete flag
  -post string         Obsolete flag

Other:
  -v/verbose int       Set the verbosity level.
        0 to turn off messages
        1 for fatal errors only
        2 for all errors
        3 for warnings
        4 for informational messages
        5 for progress messages
        6 for detailed debugging messages
  -rt int              Specify the number of rendering threads. 1 to 4
  -rnm boolean         Network rendering option. If true, mental ray renders
        almost everything on slave machines, thus reducing the workload on the
        master machine
  -lic string          Specify satellite licensing option. mu/unlimited or
        mc/complete.
  -reg int int int int Set sub-region pixel boundary of the final image:
        left, right, bottom, top
*** Remember to place a space between option flags and their arguments. ***
Any boolean flag will take the following values as TRUE: on, yes, true, or 1.
Any boolean flag will take the following values as FALSE: off, no, false, or 0.

    e.g. -s 1 -e 10 -x 512 -y 512 -cam persp -of jpg file.

Donc pas grand chose.
Je te suggère en effet d'utiliser le flag  -preRender et de charger un MEL contenant par exemple setAttr "miDefaultOptions.minSamples" 0; setAttr "miDefaultOptions.maxSamples" 4; pour régler l'AntiAlias à 0,4.

C'est un peu bourrin, mais cela devrait marcher.
Enfin si tu trouves mieux, je suis preneur. 

Merci pour ces infos m'sieur, cela va m'aider aussi pour notre rendu du 30secondes