Process for changing the syntax, resolution and bitrate of MPEG bitstreams, a system and a computer product therefor

A system for generating an output MPEG bitstream from an input MPEG bitstream, said output MPEG bitstream having at least one entity chosen among syntax, resolution, and bitrate modified with respect to said input bitstream, the system comprising:

• a sorting module configured to distinguish in said input bitstream, first portions and second portions that respectively substantially do not affect and do affect the variation in bitrate;
• a syntax module configured to subject said first portions of said input bitstream to the translation of said syntax into the syntax of said output bitstream, said syntax module configured to transfer said first portions subjected to syntax translation to said output bitstream when said syntax is to be modified between said input bitstream and said output bitstream;
• a resolution module configured to subject first portions of said input bitstream to the translation of said resolution into the resolution of said output bitstream, said resolution module configured to transfer said first portions subjected to resolution translation to said output bitstream when said resolution is to be modified between said input bitstream and said output bitstream;
• a transfer line configured to transfer said second portions from said input bitstream to said output bitstream in the substantial absence of processing operations when said resolution is to be left unaltered between said input bitstream and said output bitstream;
• and
• a processing set configured to subject said second portions of said input bitstream to a filtering in the domain of the discrete cosine transform and configured to transfer said second portions subjected to filtering in the domain of the discrete cosine transform to said output bitstream when said resolution is to be modified between said input bitstream and said output bitstream, wherein said processing set includes at least one element configured to scale a motion field in order to enable association to pixel macroblocks having a resolution corresponding to the modified resolution of said output bitstream;
• wherein said at least one of the macroblocks is from a set made of:
• macroblocks that are to be merged into a new macroblock;
• and
• macroblocks that surround the macroblocks that are to be merged into the new macroblock;
• wherein said at least one element is configured to apply to motion vectors associated with said input bitstream a transformation to correlate the motion vectors to a given number of motion vectors associated with at least one of the macroblocks, wherein said at least one element is configured to:
• multiply said motion vectors by respective weighting factors;
• accumulating the results of the above multiplication;
• and
• divide the results accumulated by the sum of said weighting factors.

A computer program product directly loadable in the memory of a digital computer and comprising software code portions for causing a computer to generate an output MPEG bitstream from an MPEG input bitstream, said MPEG output bitstream having at least one entity chosen among syntax, resolution, and bitrate modified with respect to said input bitstream, by:

• distinguishing, in said input bitstream, non-affecting portions that substantially do not affect variation in bitrate and affecting portions that substantially do affect variation in bitrate;
• subjecting said non-affecting portions of said input bitstream to translation of said syntax into the syntax of said output bitstream by transferring said non-affecting portions subjected to syntax translation to said output bitstream when said syntax is to be modified between said input bitstream and said output bitstream;
• subjecting said non-affecting portions of said input bitstream to translation of said resolution into the resolution of said output bitstream by transferring said non-affecting portions subjected to the resolution translation to said output bitstream when said resolution is to be modified between said input bitstream and said output bitstream;
• transferring said affecting portions from said input bitstream to said output bitstream in substantial absence of processing operations when said resolution is left unaltered between said input bitstream and said output bitstream;
• subjecting said-affecting portions of said input bitstream to a filtering in the domain of the discrete cosine transform, then transferring said affecting portions subjected to altering in the domain of the discrete cosine transform to said output bitstream when said resolution is to be modified between said input bitstream and said output bitstream;
• and
• scaling a motion field to enable association with pixel macroblocks having a resolution corresponding to the modified resolution of said output bitstream when said resolution is to be modified between said input bitstream and said output bitstream, wherein said scaling of the motion field includes an operation of applying to motion vectors associated with said input bitstream a transformation that correlates the motion vectors to a given number of motion vectors associated with at least one of the macroblocks;
• wherein said at least one of the macroblocks is from a set made up of:
• macroblocks that are to be merged into a new macroblock;
• and
• macroblocks that surround the ones that are to be merged into the new macroblock;
• wherein said transformation applied to the motion vectors associated with said input bitstream comprises the operations of:
• multiplying said motion vectors by respective weighting factors;
• accumulating the results of the above multiplication;
• and
• dividing the results accumulated by the sum of said weighting factors.